The best way to deal with problems like this is using lagrangian mechanics to look for stable equilibria. You basically think of the full configuration of the system as a point in space, and look at how the energy will change if you make small movements. Although both the hole at the bottom and top would be equilibrium points, the hole at the top is not a stable one. It's been ages since I was a student and we worked out these spinning top problems, and I don't really have time to do it all again now, but it actually becomes pretty easy to understand these systems when you look at things using generalized coordinates and the principle of least action rather than trying to work things out using forces. Energy-based reasoning turns out to be much easier than summing forces if you want to analyze and understand most rigid-body systems.
I did the experiment, and it was not logical at all. when the whole was on the bottom it was stable but when flipped over with the whole on top it loses speed and acts strange.
Energy based analysis doesn't feel intuitive. It feels like a higher level overview with interesting details hidden under the hood. While analysing via forces is difficult, you get the knowledge of each working part.
I decided to build a tippie top in my shop because of this video. I'm now subscribed to your channel and have thoroughly enjoyed catching up on your videos.
0:20 The greatest minds in modern physics and not one of them thought, "If we spin this on a table or work bench, we can see it better, and we won't need to bend over like this."
They probably did the experiment informally this way because they felt it was a curiosity instead of real physics. Bohr brought that same ignorant/egotistical attitude to Solvay in 1927 and convinced physicists that you cannot know anything about how nature works until you make a measurement--then, according to him, the mystery ends and reality begins. Most physicists still believe this unscientific Copenhagen Interpretation today, in spite of at least two other interpretations of quantum mechanics that are deterministic and eliminate the mysterious wave function "collapse". The de Broglie-Bohm interpretation even has the support of several experimental verifications!
@@david203 They weren't doing an experiment, they were playing with a child's toy. As to the rest of your comment, I'm not sure what your point is. Are you pointing out that scientists can be wrong? If so, I agree, because *EVERYONE* can be wrong. Science is designed for this. Properly done it efficiently eliminates wrong answers. Of course, it not usually done completely properly. That's one good thing about it. If you don't do it right, someone else will.
@@erictaylor5462 Yes, they might simply have been playing with a toy; perhaps I gave them too much credit. But my point (perhaps off-topic) is simple, and I stated it clearly. Ever since 1927 most physicists have agreed with the Copenhagen Interpretation (look it up if the term is unfamiliar), which enshrines mysticism in the operation of Nature in the realm of the very small. This mysticism involves many specific aspects, such as an unavoidable ambiguity between particle and wave behavior, and especially an inability to know what particular quantum state a particle or experiment is in until and unless it has been observered or measured. Some physicists have even called for a special role of human consciousness in the process of observation. All of this mysticism goes away with the interpretation of quantum mechanics (the wave function) known as Bohmian Mechanics, which was published in Physical Review in 1952 and has since been confirmed by several experiments. It also goes away in the Many Worlds interpretation of Everett. Both of these interpretations also generalize easily in larger regimes to form the formulas of classical mechanics, such as F=ma. Yet Bohm's work is ignored or rejected by most physicists, not based on merit, but based on history: David Bohm was falsely accused of being a Communist (because, like many intellectuals, he had attended some meetings) and as a result was barred from the Manhattan Project by Robert Oppenheimer, who explicitly asked all physicists to have nothing to do with him. Bohm left physics for awhile, learning Eastern philosophy from J. Krishnamurthi. He returned later with one final paper, which also was largely ignored. I recommend the largely nontechnical book "Making Sense of Quantum Mechanics", by Jean Bricmont, Springer, 2016, for further information about how mysticism can be eliminated from standard quantum mechanics. There are also much more complete (and more expensive) books that present the complete mathematics and experimental evidence to back up the return to determinism that marks this interpretation. I hope I have clarified my position to your satisfaction.
It has to do with balance. To explain in a "hands on" sense, take a broom and balance it on your hand, counter-intuitively it's easier to balance it with the heavy side up...that's because a heavier object is more difficult to move than a lighter object...but you're controlling it not at the top side, but at the bottom. Same as the spinning disk. The demonstration on the ice removed the focal point so there was no balance due to a lack of friction, So the answer was inertia and centripetal force...and the conservation of energy. Inertia dictated how best to conserve the centripetal force.
exactly. But what when the hole turn downward in middle air? I don't know how many times he did that one but I think that the disk didn't stay enough time in middle air and just turns when in contact with the ground. what do you think?
Spinning on ice is a very nice example, because it behaves differently. I suggest, that because f.ex. stone is responsible for more friction than ice, the ring once tilted doesn't actually rotate around its axis, but is rolling in a small ring and so it is changing the place of the hole. On ice, it behaves more quickly and it seems to be chaotic, because to get some friction on ice is harder.
What if the "holes" were unequal in size (and therefore mass - or lack thereof)? THEN IT would be very unstable at 3-9 but seems it would spin at 6 and 12
This is Gyroscopic procession, the mass if offset which will alter the area of force, as the mass spins the force location will be off axis due to the procession effect which will make it favor the lighter side, and once it's in this state it will be stable. So due to the gyroscopic procession effect the stable location isn't where the weight is, its on the other side.
+1EyeSack1 I think you mean while it is floating? It can be in a vacuum but if there is still gravity keeping it on the surface the effect will be the same. They need one of these on the ISS.
no air and no gravity aren't mutually exclusive. A vacuum can be here on Earth if you suck all the air out of a chamber. We keep telling him to try it in a vacuum but he never replies.
The spinning disk differs from the tippytop, though. The tippytop has a central axis upon which to spin, keeping all of the matter evenly distributed, while the spinning disk has a hole interrupting the central axis, with matter distributed unevenly around it. The disk wobbles more as a result. Regardless of which toy is used, rotational stability matters. With more mass at the base, the center of gravity is lower, but the length of the axis above the center is greater. Axial variation is exaggerated over the longer distance and has a greater effect on rotational stability. With more mass at the top, the center of gravity is higher. The axis above the center of gravity is much smaller and insulated by the greater mass, so axial variation has less distance to be disruptive. Ice causes trouble because it undermines the stability of the axis at the base. Unlike a tippytop where the axis centers around a very small point of contact, the spinning disk has its entire circumference to use as a point of contact.
I done the experiment, and i really did not see him spin it with the whole down, but when i did it when the whole was down the disk was more stable and lasted longer. what do you mean the length of the axis above the center is greater? i am just trying to understand what is going on.
How about some controlled experiment, like mounting that thing in a bearing mounted on an adjustable axis and spin it up with a good blast of air. To go further start in a sealed chamber and then suck the air out.
I wonder. Have you tried spinning such a disc in a vacuum? I would have assumed that centripetal force was the culprit, but noticing the difference between smoother and rougher surfaces made this very interesting to me :) Thanks
I have a suggestion Make this model on 4 different axis to form something like a ball with a hollow ball at some side That will eliminate 2 axis factor of unbalance and a lot of other factors. If the greater mass tends to go to the top which is expected as in the toy you mentioned I guess that will totally mean inertia is the main factor. I'm just an architect and I have no idea what I'm saying.
I'm guessing, not completely sure, but I think maybe it has something to do with the alignment and relative positions of Centre of Gravity, Meta Centre and Centre of Buoyancy... An object when immersed into a fluid (which is air here) is under Stable Equilibrium if it's Centre of Buoyancy is below the Centre of Gravity, otherwise it will have Unstable Equilibrium and it will try to attain stable equilibrium while it can (i.e, in this case, while spinning). Eg: An egg shaped dense object will sink into the water with it's larger side in the bottom. No matter how much you try you will not be able to make it sink down with its smaller side down... (which is quite opposite in this case... I know I'm contradicting my own statement... my physics is bad... forget you even read all this lol :P )
I discovered this phenomenon when I got my high school ring and noticed that no matter how I spun it, the heavy side always goes to the top. A ring works much better than the wooden disk because you can spin it faster, and there is no wind resistance that the wooden disc may encounter. I asked a PhD in Mechanical Engineering to explain it to me, and he said I didn't know enough physics to understand the answer.
+Randy Rickleman what about the fact that the spinning top's small side has less air resistance, even without the hole it has less area where air affects it.
+Aditya angara, the air not impact like for the gravity on 2 separated items, because you have only one item. Or if the air impact on any part of the disc, it automatically balanced by the other side of axes rotation part which doesnt have a hole.
To me, it seems very similar to the situation involving a wing nut spinning (in space). When you spun the circle on ice, it seemed to favor hole up and/or hole down, but couldn't make up it's mind. So the initial flip is caused by this effect. However, friction and leverage are the "dynamic duo" creating stability when hole down. The object is resting on the bottom most point, and friction takes hold, moving the point of rotation (at least partially) from the center of mass to the point of contact. Since the center of mass is at it's furthest from the contact point in this orientation, leverage joins the party. Think of the video about gyroscopic procession, when you had a large spinning weight at the end of a 3-4ft handle. It would be much easier to change the systems orientation if you were applying force to the wheel with a short handle rather than a long one. TLDR: Conclusion is gyroscopic procession approaching gyroscopic stability due to the magical force of gravity, friction and mechanical advantage. I'm not sure if any other means of applying force could be used to create this stability. Magnetism perhaps, though nonferrous objects would be unaffected. Not sure how spinning metals in magnetic fields would play out either. Watched Spinning disk trick and solution right after watching Stand-Up Maths video about spinning objects with an egg shape. Your circle is like a 2d mass simulator of egg shaped objects (although still slightly 3d I guess). I hope at least some of what i've said makes sense and is correct, and hope it helps someone to understand what we just witnessed.
My hypothesis of why the disk does the flippy thing on the ice could be because as the mass goes to the top, the disk would try roll along the plane of the disk, causing the disk to want to move like a wheel of a moving bike. When the linear motion combines with the spin, the wheel would tip and the center of mass would be vertically off-set from the point of contact with the ground and the plane of the wheel causing it to make a sharp turn every time the hole flips. Its basically like when you roll a tire of a car and then push the front of the wheel sideways, as it falls over, the friction of rolling of the tire catches the center of mass causing causing the wheel to make a really long continuous sharp turn, loose speed and eventually fall over... Basically it wasn't spun fast enough. Why that happened more frequently on the ice instead of the stone ground was most likely because its harder to keep stability on ice skates while preforming this experiment.
Hmmm... good question. Wonder how it would react in a vacuum. Also... what if it was spun (non-humanly of course) precisely vertical and perpendicular... I think you know what I mean. A precise A and B axis ? Is that what I mean ? heheheh.
sure, but he also showed the top that does the same thing, and it doesn't have any holes, implying that the air going through the hole isn't very important here.
I think its a combination of friction and centrifugal force. The friction is constant throughout and at first causes the disc to want to wobble. Once it wobbles centrifugal force comes into play causing the larger mass at the bottom to want to move toward the out side of the rotation, and it then begins to counter act some of the friction. It stays mostly at the top because every time it wobbles off center centrifugal force increases the counter to the friction.
Isn't it the same reason that a tennis racket spins over the x-axis when you flip it over the y-axis? I thought either you, Smarter Every Day or Mark Rober made a video about that fenomenon.
Two thoughts/questions for thought 1) As I recall, ice isn't really slippery: wet ice is. Ice skates slide because the intense pressure under thin blade increases the melting temperature and there is a thin film of water.....2) Is it possible that their is some gyroscopic effect difference that raises the heavier (actually the more massive) part to the top.....3) if a pin were anchored at the very bottom, and the disk is balanced (equal density board, symmetrical hole, etc.), could it be spun on its pin if spun without some "off-center-ness caused by your hand to start it off with? (why does a child's traditionally cone shaped "spinning-top" spin with its greatest mass high above its point? (good night, its too late for me)..PS thanks for your work, I find it stimulating and thought provoking.
What an amusing video I enjoyed it My perception on this is that a lot of things come into play some maybe accurate or some maybe wrong yet possible to consider Firstly we take the the circle Of about 20cm in diameter and 10mm thick We spin it like how we would spin a coin and it wouldn't do the switch as such Now we take into consideration of the surface area and the balance of the object draw a half way line horizontal and vertically to give 4 sections of the circle near the edge of the circle at the end of each line we have North, East, South and West Now if we cut a hole of centre like for example Northeast We will affect the the spin of our circle disc Things to consider 1-Aerodynamics 2-Resistance 3-kinetic momentum 4-surface area 5-speed of the spin Ect...... When we take our solid disc with no of centre hole the energy is consistent until it loses the momentum Now when we put the disc in a spin with an off centre hole everything changes yet eventually it will lose momentum it depends on how fast you spin the disc anyway back on topic by having the hole off centre the surface area is reduced and increased at the same time it has reduced by allowing air to pass through the hole creating its own drag or kinetic energy which is transfered to kinetic momentum by being of balance the hole becomes a centre point thus the increased surface area which will be where the hole isn't provides the energy to increase the kinetic momentum and eventually or quickly rotates its self round and creates uplift drag and downwards drag thus the hole be at the bottom and the solid mass near the top I'VE WRITTEN THIS IN MY OWN WORDS TO HOW I PERSONALLY UNDERSTAND TO THINK IT WORKS NOT SAYING I'M RIGHT AND NOT SAYING I'M WRONG IF YOUR A PHYSCIST YOU WILL UNDERSTAND WHAT I'M SAYING OR TRYING TO SAY AS I'VE WRITTEN IT IN MY OWN WORDS
Here's what i think is happening: As the disc spins it leans to one side and starts rolling, changing the orientation of the cut out hole from top to bottom. If you spin a coin, as it slows down it starts leaning to one side and starts rolling on the spot at a 45 degree (or so) angle, rather than spinning completely upright. A good example in the video is at 2:28, you can see a predominant lean to one side (the side with the tape) start to develop, this causes the disc to effectively start rolling in a very tight circle and you can see that the point of contact with the ground is moving in a tight circle beneath its center of gravity. Further evidence in the video, if you look at 2:32 the disc is upright and shows no sign of rotating over. It is only at 2:35 when the disc loses balance and starts leaning to one side that it actually starts rotating; surely if it was flipping due to inertia or centripetal force then it would start rotating immediately after it is let go? Please share your thoughts as a comment, tell me if I'm wrong, tell me if im right.
I think I understood it :).. It is kind of related to stuff like the gimbal lock phenomenon... Firstly, the spinning forces a Gimbal Lock situation on the wheel.. Since the 'two circles' (one 'positive' and one 'negative' (a hole)) are on the same plane, they will share the rotation.. But the larger circle is 'unlocked' (you can spin it any way you want), and the smaller circle ('hole') is 'locked' (you can not spin the hole).. The rotation axis will be the same for the two circles, but for the smaller circle, the object is dislocated from its center of rotation (from the rotation axis).. This axis offset, combined with the gimbal lock will force a Y rotation for each Z rotation angle until it is really 'locked' (the smaller circle on its most lower position). Well, i think this is it =D...
To explain why the hole moves downwards when the disk is spun in mid-air is quite easy. Consider a piece of rope hanging downwards from your fingers and make it spin along the vertical axis. It then has two equilibrium configurations: an unstable one where ik keeps hanging vertical whilst being spun and a stable one where it is swept around diagonally so that the “centrifugal force” and the gravitational force (and the tension in the rope) cancel each other. Exactly the same is happening when you let a wooden disk hang from your fingers and make it spin. It will attempt to reach the stable diagonal configuration. As you release the disk while doing so, it will continue this motion (from vertical to diagonal) in mid-air, hence the hole will move downward (and then upward, downward, upward, etc.). So in this case, the presence of the hole in the disk is of secondary importance. Exactly the same motion (from vertical to diagonal) would happen it the disk had no hole. You can also perform this experiment easily with a pencil hanging from your fingers. Spin it along the vertical axis and release it in mid-air. As the pencil falls, it will turn from vertical to horizontal to vertical, etc.
This reminds me of when I was younger I would take whiteout and draw a stick figure with its arms and legs stretched out on a coin and spin it and then it would look like it was doing cartwheels.
Hey, Well I would just like to add what I think is happening. Just as you had mentioned the centre of mass lies towards the heavier side, and not at the disks centre. This is my observation one. Secondly, let us consider the clip where you drop the disk from a few inches above the ground, and still the disk behaves as before. Now let us just talk about centre of mass (CM) and centre of gravity (CG). A body to be in a state of rest when placed on a surface, the CM and CG must coincide. IF they do not coincide, then the friction at the surface of contact, should be large enough to negate the torque created by the non coincidence of the CM and CG. Now considering the most stable position for the disk to be, is where the heavier part being down. But that is when it is in rest. But in our experiment, the disk is rotating. And bear in mind, that the rotation causes wobbling. The first instance the disk wobbles, the CG and CM no longer coincide. This creates a torque CM. Leaving it here let us look at another piece of the rotating disk. The base, which is in contact with the surface. here, duo to the wobbling effect of rotation, the surface experiences non uniform pattern of friction. This is true even for the rotating top, because, one edge is leading, and the other edge is trailing. The leading edge experience more friction than the trailing edge. This change of torque duo to non coincidence of CM and CG, and the non uniform friction at the bottom, causes the disk to flip. My guess is that, if my theory is right. If we spin the disk with enough force to sustain a spin that lasts long enough, the disk would progressively tip itself upside down over and over again. Please do share your views on my theory.
The important thing to notice is that, once the disc is spinning upside down that torque reverts direction and creates a RESTORING FORCE that keeps this situation more stable. This stability only occurs because of dragging forces of contact. When you try that on ice, drag forces are much weaker and stability is not so promptly attained, so there may be a number of flipping before the disc eventually stops.
7Earthsky it should fly upwards wobbly, but rotating on the reverse center of travel it rolls on, I think, for the same reasons, released as upward motion. drag in reverse.
My bet is that the answer is in how you spin it. I can't work it out in my head atm (it being 1:30am) but I bet since you are spinning manually, it ends up landing at an angle. Since the center of mass is off center relative to the bottom, it applies a torque. Then like you thought, precession kicks in. The torque pulling down on the COM, starts shifting the angular momentum so that it ends up spinning around like a wheel. My bet for the reason it stabilizes at the top is probably a combination of factors. It could be that the COM lines back up with bottom and the torque stops. Friction could factor in because after the COM stabilizes over the bottom, friction may be stopping the wheel-like rotation. Which may explain why on the ice rink it spun out of control a little bit, because friction didn't help it stabilize. Once that rotation is stopped and it stabilizes on it's head. It could be that since it's stabilized and the COM is now centered, there any torque to spin it back to the bottom. EDIT: Just watched the alien video. My explanation ends up similar but different. Was worried after I realized I hadn't watched it that it would nullify this comment.
I don't buy the explanations given. I've thought about this problem on and off for months. Nothing I've come up with makes sense. However, when you form an hypothesis (friction), test it, and the test fails, you don't get to keep the hypothesis. The friction hypothesis should support a slower change with less friction, not a faster one. This is a case where "I don't know" is a perfectly acceptable answer.
Jeff, if you want to know the true answer, stay tuned for my #AntiGravity Part 6 video. And yes you are right, "friction" is not only not the answer, the true nature of "friction" is also very misunderstood. #StayTuned
Okay, I'm just about to graduate a 2 year electrical program in Ontario, but let me try my hand at physics. An object in motion, will stay on motion, right? So, with the disk spinning vertically in position 0 in space, nothing would happen(the hole would stay at the top). On the ground, gravity is creating friction on the side on the ground. This will move the object's point of balance away from the point of contact from the ground (vertically speaking). Since the point of balance would be not in the center of the disk (one of the other commenters described a broom like this), as the heavy bottom of the disk moved one way, that force is reflected across the point of balance and is magnified slightly on the light end. Keep in mind that both the force of friction and the reflected forces are subject to gyroscopic procession. If we now consider the disc to be spinning on an angle, we would see the heavy end and light end moving up and down at 45 degree angles to the horizon. Keeping in mind that the force on the light end will be greater than that on the heavy end(due to the off-center point of balance) and the heavy end has more mass, the gyroscopic procession(GP) effects are more noticeable. The heavy end will be pulled down by gravity, however GP will translate rotate that force 90 degrees. That force gets translated to the other side of the disk and amplified AND I believe that force then is affected by GP again, pulling the lighter side down more than the heavy side. I expect that the difference between the disc and the spinning top is air pressure. Hmm... I wonder if David Hamel's device used this principle? For the record, this is a guess. I haven't taken any physics classes.
I study physics at La Sapienza University of Rome, and I had a lecture about the gyroscope (top) problem: it's all the things you mentioned put all together! Nutations, recession, friction and obviously the conservation of the inertial momentum... on ice, you eliminate the friction problem, but you have some big ass nutations because you weren't able to make it spin precisely on the axis, so i will go down but won't stay down.
I think the behavior in the air has a simple explanation: Your disc is asymmetric and thus has distinct moments of inertia about its 3 principal axes. Your initial spin is about the axis with the intermediate moment of inertia. This is well known to be unstable and will wobble resulting in the observed "rotations". You can check this by initially spinning the disk about the axis with the lowest moment of inertia (rotate the disc by 90 degrees and spin) and launch. Here I would expect the spinning to be stable. I would expect this effect to also influence the spinning in a surface, especially on ice, although the torque would also have to be included.
I see that most of you can't figure out how the friction actually affects the angular momentum of the disk, I'll try breaking it down so you can understand. Let's assume that the disk is spinning clockwise. The angular momentum is pointing downwards. A torque is generated from friction due to the asymmetric spin. When Derek says that the angular momentum is decreased in the '3' direction, he means that the vertical spin(i.e. the axis along the marked line) of the disk is slowed, and in the '1,2' direction, he means that the horizontal direction(i.e. the axis along the red dots in the thumbnail) is spun up in the clockwise direction. The disk, then, turns over until it is spinning with the line horizontal. Once the disk reaches this point, the torque is in full effect, and the torque spins up the disk along the line in the clockwise direction, and the horizontal spin is spun down by the torque, until the disk turns over. The end result is the disk spinning with its hole as close to the ground as possible. I hope this clears up some confusion.
Actually It's Not Just Surface Friction ! The Air Has Friction Too And As Its Even More Connected To The Air The Air Force Is More Effective Than The Surface ! But The Ice Hall Is Cold More Air Molecules Are Packed So That Is Puzzling For Me :-(
I wish it was the air, but i have done the experiment with a way smaller disk that has less surface area for the air to make much of a difference, and it is more stable when i spin it with the whole on the bottom. when the whole is on the top it acts strange it does not spin as long and moves the whole around more often.
Friction is a part of a solution in this experiment. Object want to keep moving where less resistance is there. Therefor any upset in the object of such formation in a proper heavy side down would mean that any change would force the object further down, and increase friction even more. In the other way, heavy side is up, and there is room to move the center of gravity down by slightly rotating, and still remaining in balance. If you spin it on perfect axis with heavy side down - it will remain that way. (from other video with iPhone spinning). In no gravity and no friction environment is would keep on spinning in exact way, as you span it in first place. Also there is gyroscopic effect, which will keep it spinning, BUT as it flips, frictions comes in full tilt. On ice (not dry ice) it would change the positions of center of gravity due to friction changing from place to place, is ice is slippery when pressure applied, and at such scale, pressure difference is massive, taking the balance out is easier for mother nature and father physics. Also on parts, where ice is already molten, no pressure needs to be applied in order to decrease friction, so it keeps on going out of balance, and you get the weird wobbly thing. I am not sure, just got to think about it. Other comments suggest that it might be the hole in the ring - it has nothing to do, or at least play very, very VERY VERY VERY little effect. Yes air is less dense the higher you go, but it is neglegible(i do not know how to spell it), just like 1 human in the universe, but together humans(humen?) become a power. BOOM THERE IS NO CENTRIFUGAL FORCE! Watch you language, it is called centripetal force. Centrifugal is your laundry machine.
I think this is actually a form of precession, and the reason is not solely the ground. If there is a hole in the upper part of the disk and you (persumably) rotate it in the slightest unblanaced way (torque and mass wise), you actually creates an imbalance with the forces (pulling it down), thus creating an effect similar to what you described with the friction. I think this is why you get that behaviour also when thrown from the air (this is also the explanation for the spinning top)
Differentiating the angular momentum with respect to time will yield a set of differential equations where the angular velocities in the horizontal plane are coupled as: Wxdot = k*Wy*Wz + CG Offset Term prop. to y accel + X Moment Wydot = -k*Wx*Wz + CG Offset Term prop. to x accel + Y Moment Without the CG offset terms, the solution simply reduces to cosine and sine functions which implies neutral spin stability. Including the terms will result in two stable configurations as mentioned below.
i think it is that the greater mass at the bottom of the initial spin, like you said, is being acted upon by friction and torsion to push it toward the outer edge of the rotational circumference, and since the object is a solid mass it cannot travel beyond its physical boundary, so it travels upwards along that physical boundary and as it reached the top, the angular momentum of the spin is causing the mass to seek stability and that is what keep the heavier mass up top.
When you spin it, the wheel is NEVER COMPLETELY aligned perfectly straight up and down, which results in the weight of the wheel redistributing itself because of the force pushing the weight away from the center. When the hole reaches the bottom of the wheel, THAT IS THE FIRST TIME that weight is redistributed evenly and the weight being pushed out on both sides become's relatively equal which keeps the hole on the bottom. I've also noticed that the rate at which the hole rotates around the wheel on ice stays pretty constant. This could be because of less friction that ice has, since the wheel is not only spinning, but also rotating. It'd be like rolling a hoola-hoop backwards but throwing it in front of you. If you did it on ice, the hoola-hoop would stay in the same spot but continue to spin for a brief amount of time. just add rotation and that accounts for the Ice test. I'd love to hear your thought's on my response :)
I know I might not be right,but think of a spinning top. A top has a large mass spinning on a single point. However, if the top is spun upside down it won't spin for some reason. I remember as a kid I had this top that you spun rope around, and when you launched it, you would toss it upside down and pull. The top would hit the ground and then fix itself onto the metal tip on the other side. As a kid I always wondered why it had to be upside down, But if you think about it, if it's upside down then you will have a greater surface area giving it more friction with the surface it is spinning on.Then you go through the process described in the video until the spinning object finds the point at which the larger mass is at the top and the point or smaller mass is at the bottom. Basically, what I'm saying is that when an object (like the disk or a top) is spinning, the object will always try to spin on the closest thing to a point. In the case of the video, it's the lighter side of the circle. One more thing I've noticed. For the object to turn around on to the other side and spin, it must be round. The spinning top I had as a kid was rounded, so were the top and disk in the video. Think about that. I hope the people of Veritasium see this and that this helps them.
It's about the two equilibria. The system favours settling into the more stable equilibrium. It's just like how a pendulum usually stops at the lowest point in its swing and not the highest possible point, even though they are both points at which the pendulum does not accelerate from gravity.
How can you say it doesn't exist when you follow that statement up with a definition of what it is? If that is what people mean by the term and it accurately describes what is going on , then by definition it does exist.
It's a common term which virtually everyone inderstands and explains the phenomenon. I don't know why pedantic pseudo-intellectuals pretend to not understand what someone is trying to say when they use the term but they just do.
I would suggest it has to do with a fine balance between centrifugal force and angular momentum. If we consider only the motion of the center of mass (air flow through the hole doesn't matter - a non uniform disc with off center center of mass would probably behave similarly) then there are 2 different effects. Seen face front the center of mass starts from the bottom and rises up to the middle (call this, part A of the motion) then from the middle to the top (call it part B) Seen from the top part A shows the center of mass starting from the middle moving outwards which can be explained by centrifugal force. In this position however (with the disk spinning and the center of mass found in the middle - equatorial motion) the angular momentum of the center of mass is always changing (radially outwards) so the center of mass gradually rises untill the angular momentum points upwards because at this point the spin of the disk does not change the direction of the angular momentum of the center of mass.
The reason why the disk "flips" over even when you spin it in the air is the exact same reason your cell phone flips over when you try to flip it in the "5 Fun Physics Phenomena" video - any asymmetric body will have two stable axes of rotation, and one unstable axis of rotation, depending on which principle moment of inertia is "in between" i.e. not the biggest or smallest of the 3. Because it's unstable, any slight deviation from exactly perfect initial spin will cause the disk to rotate along it's other axes, and because the center of mass isn't in the center of the disk, rotation about these other axes causes the "orientation" of where the hole is to change, If you checked that disk, you'd find that rotation about the other two axes are stable. No idea why it's stable when you spin it on the ground though - friction seems like the best bet.
Sad I caught this video 8 years later... This sounds a lot like something motorcycle chassis design engineers have been working with for years. Where bikes with higher center of gravity need more input to steer fast through corners and "s" bends but once enough "input" is applied, they steer faster through the 'S' bends than a bike with lower center of gravity. While steering input can be supplemented and enhanced through mechanical means this leads to an all encompassing chaos of other factors like steering angle, trail, direction of rotating masses, tyre traction, etc. Very interesting problem with great practical implications!
If you'll notice, when you spin a regular top that has a pointed bottom, it will move in a little circle, or wobble in place, because that point locks it to an axis. The disk and the round-bottomed top don't have that ability, because they lack a point on the bottom. Because of that they can roll over, aided by the force of their rotation and the friction of the ground. In the case of the toy that flips over, the top part has a point on it to rotate, so when it rolls over it then becomes locked to an axis and rotates around it. I'm not sure I explained it well but that's what's happening here.
The comments about Lagrangian energy analysis have it right. Call this the principle of least action. A better example is to use a class ring as often given out in sports. They are smooth and rather spherical, but heavy at one end. With a gloss of baby oil on a glass surface, the friction is minimal and central. Spin the ring heavy end down and it will go for a long time and invert exactly once. This is not the Dzhanibekov / tennis racket / intermediate axis effect, because it flips only once. Dzhanibekov is a mechanism in the flip, but the disk / ring becomes stable at the position with the least kinetic energy. (Thank you, Chuck Winall (sp?) for showing this to me at Cal Tech about 50 years ago.)
I have an intuitive solution for you: Maybe, when the disc rotates, it creates a force that lifts it slightly upwards, like a helicopter. The force cannot be very large, therefore the result is just a displacement of the center of mass from the bottom to the top. The slight angle that the disc has initially, contributes to the displacement of the center of mass, as well as the speed which it rotates. I have not done any experiments, but off the top of head, this is it for me :)
I think it has something to do with mass trying to find an equilibrium in its constraints. The mass is being pushed away from the center, it is also attached to that central point and moves in an arch to an axis point; either up or down. When down that force is pushing against the ground causing a rebound and directing energy back up through the disc, nudging mass off axis and starts a loop. Eventually, the mass passes the mid point and will settle at the top. The mass is still being pushed up and pulled to center till energy diminishes enough for the effects of gravity overcome the influences upwards. The disc should be lighter on the scale when spinning the mass on top as compared with spinning mass on bottom, if this thought holds water. It also makes me think of the spinning T they demo in space. How it flips back an forth. Maybe it’s the same as that, just shape not allowing for flip back down once up? Additionally, you have that demo of the spinning mass on a rod being easy to lift in one direction and hard to lift when spinning opposite. Does rotational direction play a role in how the weight moves? Is the marker pattern different when observing?
3b. This also pushes the part of the disk with the most mass to the furthest from the axis, positioning the hole at the bottom. Key points: A. This explains why the disk behaves strangely on ice. Without the drag of the ground, it isn't forced to stabilize its spin. B. Based on my explanation, it would flip regardless of if the hole started on the top or bottom, and would then stabilize. This would be validated if you spin the disk with the hole at the bottom, and it flips to the top.
since A is now in contact with the ground, friction would not permit it to spin all over the place.Since B has more inertia compared to A it would not behave as erratically and so the disk would be forced into some sort of 'equilibrium'. Since ice has considerably less friction then A would not be locked to the bottom. And when the disk is airborne the center of gravity of the system would move to the point farthest from the bottom as it is the most stable orientation as with anything suspended
Interesting to try different sized holes and the holes in different places. For instance, a hole in the centre - how much off of the centre does the same size hole need to be to cause the flip and various states in-between. Adding this dimension could bring in some pretty wonderful maths.
Think about this. Different angles going in same direction, and at the same time, opposite direction of themselves. If it were a clock, the rotation is 3 going where 9 is, and 9 going where 3 is. But think that 4:30 is going towards 10:30. Which is why the down right quarter is going to where the up left quarter is. But once the hole side is down, it doesnt have enough matter to balance the energy enough to go back up. That could be it. Something I just realized. On concrete, the disk stayed on the same spot. But in ice, it kept moving around. This might be why it works on concrete, and not on ice.
Note that in the spherical example the center of the ball always maintains the same distance to the floor ( r remains constant). This takes much of the confusion out of the experiment. With a disk, r can not easily be held constant.
I think it may be useful thinking of the circle as a a set of many parallel rods. So starting at the hole side up you will "build" the circle with short rods that get longer as you go up the circle until the hole, at which point it becomes broken into two sets of smaller rods until you pass the hole and the rods become long single rods again that increase size for a bit until the center of the circle and then begin decreasing to the top. Thinking like this, although more mass is above the hole when the circle spins these rods rotate and gain angular momentum. Since the wooden is of uniform density the non-hole rods will have a greater moment of interia and resist gravitys pull on either end (which would cuase rotation in plane with the circle) more than the smaller rods at the base would. The net effect being that although the rods at the base have less mass to be acted on by gravity they resist gravity less then the more massive top rods and fall to the bottom, allowing the system as a whole to come to its lowest potential.
I really love watching your videos. That allows me to work english and sciences, and subjects you study are really interesting! Continue to perform from that way, you're making great job
Maybe someone else has solve this already, but I believe I understand intuitively what is going on.... so let me try to explain it and see if it makes any sense. There are several factors at play here so the best way to explain it is to break it down. 1) The disc is imperfectly weighted and so is rotating in an unstable oscillation. (it will fluctuate until it eventually finds a stable position or stops) at certain points, the disc will oscillate violently due to the center of mass being offset from the center of geometry. (the further the offset, the more unstably it will oscillate) so, (point 1) it will be unstable when the hole is left or right, but stable when the hole is perfectly up or down. (since it is spinning on its rim, it will get close to, but reach neither) 2) The key variable is not up or down but distance from the center mass. Instead of looking at it as "up and down"/"top and bottom", consider that the variable is actually the distance of the center of mass to the contact point (the ground). The only time gravity affects change on the object's spin is lateral friction at the point of contact with the ground. The contact point to the ground is the main point at which unstable oscillation will inflict force to change the rotating object's path. (point 2) when the oscillation is violent and the mass is closer to the ground, the friction force applied against the object is greatest. 3) Error begets more error. The more the mass is further from the center axis, the more it will pull itself away from the center axis. so the error will accumulate and it's spin is inherently unstable. The key to why the disc prefers "hole-down" position: When the center of mass is closest to the ground(hole-up), any minor imperfection in the oscillation applies the most direct lateral friction against the ground (the kind that would cause the disc a shift its rotation path) so any imperfection in the oscillation will accumulate until there is "sufficient error" in oscillation to violently force the center of mass off from its "somewhat" stable position to the next "somewhat" stable position. when the center of mass is furthest from the ground the effect repeats, but it can only apply a fraction of the lateral force as before. Therefore it will take longer for the unstable oscillation to accumulate enough error to cause the disc to violently flip again. Therefore, (ignoring the infinitesimally small chance that the disc is perfectly centered (hole-up or hole-down where the lateral force is exactly zero) the condition where the disc remains for majority of its changing spin is with the center of mass furthest from the ground with equal weight on either side. (hole-down).
I believe that it's caused by the assymetrical weight distribution between each edge, one half of the disc has less mass than the other one, when you apply rotation, that causes disturbance, since it's a flat edged disc, the friction is greater so the disc finds grip to rotate harder as the disturbance in the weight distribution wobbles it up and down.
Following this line of thought, try spinning the disk starting with the hole on the bottom and see if it tends to rotate toward the top on the high friction surface (i.e. not ice). The assumption that the hole should be on the top leads him to always start spinning it with that orientation which skews the result, especially on the surface where the total number of rotations is both fairly low and fairly constant.
Take a rectangular block- say a 12"x6"x3/4" plywood. Try tossing it in the air while giving it a spin around each principle axis of inertia (those are obvious). The spin around the axis with the intermediate moment of inertial is unstable- always. The block (you can also use a book with a rubber band around it to keep it from fluttering), will remain in a stable spin around the minimum and maximum principle axes, but will always flip away when spun around the intermediate axis. This is seen in satellite motion and is a challenge when stabilizing rockets and missiles. The phenomena is part of rigid body dynamics- friction is not the reason. To understand this more, you need to look at: M = dH/dt; around the c.g. and analyze stability using control theory. You may have to linearize the differential equations for each axis's analysis (maybe not). A physicist may not be up-to-speed on the basis of classical mechanics (they are too busy doing physics using math only). Any dynamics and control professor in aerospace will explain this well. It is text book material for spacecraft attitude dynamics and for rigid body dynamics. Richard Feynman in one of his books talks about observing a dish thrown up in a cafeteria and the manner it spun as being the reason he got back into doing physics after being in a "rut" for a while. Try searching for "richard feynman and cafeteria spinning plate".
This is Gyroscopic procession, the mass if offset which will alter the area of force, as the mass spins the force location will be off axis due to the procession effect which will make it favor the lighter side, and once it's in this state it will be stable. So due to the gyroscopic procession effect the stable location isn't where the weight is, its on the other side.
i think it is friction that causes it to STAY upside down, but not what makes it GO upside down. when the hole is at the top, the center of gravity is at the bottom, but it is spread out over a larger area and the top half kinda runs wild having no center of gravity to rotate around. when the hole it at the bottom, the entire weight of the disk, and the center of gravity are pushing down on the lighter side. and with more weight pushing on a smaller area, theres more friction, preventing it from wobbling like it was with the center of gravity at the bottom, and it stays there. i think centrifugal force is what causes it to wobble. with the center of gravity spread over a larger area compared to where the center of gravity is, it cant keep itself stable and begins to wobble. and when you cant go left or right or down, you have nowhere to go but up. so the heavier side makes it way to the top. once at the top, all the weight is focused to a small point when the hole is at the bottom. which gives the center of gravity something to rotate around. causing less wobble and the added friction slows, stops, and stabilizes the migration or the heavier side. i know im using laymans terms. and i know i have the right idea, just having a hard time conveying what im thinking.
I have a solution that explains all the stuff in this video and follows the laws of physics: I would've thought that the heavy part of the disk is more susceptible to momentum and gforce therefore tries to revert itself to the position with most inertia and centripetal force which is the sides of the disk. As the heaviest part nears the side, it's gaining inertia which forces the heaviest part of the disk to keep going therefore flipping the disk, after the disk flips, the heaviest part tries to revert itself back to the position with most centripetal force(sides) and once again gains enough momentum to fully flip the disk, this happens continuously(unless it stablises from friction) or until the disk runs out of spin from the friction
I shall make 2 assumptions: 1. The force responsible for the torque is equal in magnitude and equidistant from axis of rotation. 2. The disc touches the ground at only one point. The force being and opposite will give only torque for rotation and horizontal velocity will be zero removing any ground friction. But the center of mass will never exactly above the point of contact. Thus the gravitational force will give a torque to flip the disc. And this will again and again. So the hollow part will go up, then down, then up and so on. It matches with his result on ice surface as friction is negligible there.
I'm no physicist, but I have a theory assuming centrifugal force is relative to mass. When the disk spins, it has an imbalance. This imbalance is not caused because of the hole, but because the disk is not perfect. When the disk wobbles to one side, that side naturally becomes the side with the most mass, due to centrifugal force. Because of this, the side without the hole moves toward this point farthest from the vertex, and thus we're left with this result! Thanks!
Here's my two cents. The same spinning mass in a more dense gravitational pull would require more energy(to reach that state) than the same in a less dense gravitational pull. Since the whole is connected mechanically, you will find that the state with the least energy while spinning at constant at both ends would be to have the hole at the point of strongest gravitational pull. Thus, the object is merely shifting to a state of less energy.
The precession motion is due to the intermediate axis theorem. You are spinning it this way on an axis that is not maximal or minimal for the shape, which is unstable.
I think that the solution is very simple. When the center of mass is above (with respect to the center of the earth that is pulling down the whole thing due to gravitational forces) the center of the circle, the force tends to align the edge of spinning to the edge of symmetry. When, the center of mass is below, the forces tend to "anti"-align the edge of spinning to the edge of symmetry in the disk. Here, the edge of symmetry is the line crossing both centers, the center of the big circle, and the center of the small circle or hole.
Wouldn't the relationship between angular momentum and density have something to do with the answer? When you start spinning the disk in the air, the side with the hole is pulled in the direction of the force more quickly than the rest of the disk because it has lower density and therefore a smaller moment of inertia. Friction then plays a part when the disk is on the ground, as seen in the differences between the ice and the concrete. But when the ground is in play, you are also including the normal force of the ground in the sum of all forces. With no angular momentum, the side of higher density will want to be pulled toward the ground. The further from the center of gravity the bottom of the disk is horizontally, the greater the torque that the normal force plays on the disk. On concrete, friction is preventing the disk from slipping too far from x-y equilibrium, but on ice, there is less friction, and a higher tendency for the base to move away from the center of gravity and create a rotational moment about the centroid. Angular momentum pushes the hole downward, torque from the normal force pushes the hole upward. With a long enough moment arm, or a small enough angular momentum, the hole will fight its way back to the top. Otherwise, the hole will be pulled to the ground.
It is about moment of a force. Imagine two sticks in a T shaped configuration. The upper left point is point A, the upper right one is B, the bottom one is C and the intersection is D. The distance between point A and D is equal to x ,the distance between point B and D it is equal y, and x = y. The distance between points C and D is equal h. If we put 50kg at point A and 51kg at point B, the only way to maintain it in equilibrium is spinning it. There is two reaction forces at the point that is in contact with the ground, point D: the normal force direct upward, equal to g*(50kg + 51kg). And the reaction (F = F1 + F2) caused by the moment of forces: g*(50kg)*x = -F1*h and the moment of force reaction in the opposite direction: g*(51kg)*y = F2*h. That reaction force F caused by the moment of force is also present at point C an it is parallel the the stick AB. That is the force that destabilize and that is why we spin it to maintain it in equilibrium. So when we increase h, F is consequently reduced and the sistem is more stable. In the spinning disk situation, when the hole goes downward it means that h was increased and F reduced. At the ice situation, there is almost no frictional force to react the moment and produce F. At the free fall situation, I think that the hole just turns downwards when the disk hits the ground. But, if the hole really turn downwards in middle air, the only possible exlanation I can think is about the difference in the center of mass and the center of gravity or some diferences in air pressure and air resistance. Sorry for the bad english.
It's moment of inertia. Because there is a difference in mass and the object is symmetrical, less energy is required to spin the hollow side, but "spin" energy must be balanced due to it's geometry, this causes it to move across the axis. I'd wager is you make two holes in the disk that are on the same axis the disc will spin with the holes in the middle.
I'd say it's the same reason why a rotating wheel (like on a bike) tends to stay locked in a position regardless of where the center mass is. Imo it turns upside down because it's easier for the heavier part to stay locked in place by disc's rotation on top and the fact that the bottom side is touching the ground makes it less likely to "wander off". If it was the other way around then the lighter part is more likely to wobble off the center because it doesn't have as much mass to keep it in place just because of the rotation and the top part of the disc is always more likely wobble than the bottom part because of the contact with the ground.
The disk is turning to a stable equilibrium. When the hole is at the top small changes in the spin massively change the inertial pattern. Once at the bottom the disk is at an equilibrium and the friction pushes it back and forth. On the ice (ie with out friction) it will still rotate down but like a spring it will pass it's intended location.
The best way to deal with problems like this is using lagrangian mechanics to look for stable equilibria. You basically think of the full configuration of the system as a point in space, and look at how the energy will change if you make small movements. Although both the hole at the bottom and top would be equilibrium points, the hole at the top is not a stable one. It's been ages since I was a student and we worked out these spinning top problems, and I don't really have time to do it all again now, but it actually becomes pretty easy to understand these systems when you look at things using generalized coordinates and the principle of least action rather than trying to work things out using forces. Energy-based reasoning turns out to be much easier than summing forces if you want to analyze and understand most rigid-body systems.
I did the experiment, and it was not logical at all. when the whole was on the bottom it was stable but when flipped over with the whole on top it loses speed and acts strange.
nerd
@@charile haha got em
Energy based analysis doesn't feel intuitive. It feels like a higher level overview with interesting details hidden under the hood. While analysing via forces is difficult, you get the knowledge of each working part.
@@VivekYadav-ds8oz true
I came here not knowing and i successfully leave not knowing. Thank you.
Same here.
👍🏾
But I plan on watching videos for each concept I don't understand in this
3:45 here it's because of the Intermediate axis theorem, as well as in the case of low friction
I decided to build a tippie top in my shop because of this video. I'm now subscribed to your channel and have thoroughly enjoyed catching up on your videos.
And still he did not reply...
!
well peter
O
0:20 The greatest minds in modern physics and not one of them thought, "If we spin this on a table or work bench, we can see it better, and we won't need to bend over like this."
lol🤣🤣
🤣🤣
They probably did the experiment informally this way because they felt it was a curiosity instead of real physics. Bohr brought that same ignorant/egotistical attitude to Solvay in 1927 and convinced physicists that you cannot know anything about how nature works until you make a measurement--then, according to him, the mystery ends and reality begins. Most physicists still believe this unscientific Copenhagen Interpretation today, in spite of at least two other interpretations of quantum mechanics that are deterministic and eliminate the mysterious wave function "collapse". The de Broglie-Bohm interpretation even has the support of several experimental verifications!
@@david203 They weren't doing an experiment, they were playing with a child's toy.
As to the rest of your comment, I'm not sure what your point is. Are you pointing out that scientists can be wrong?
If so, I agree, because *EVERYONE* can be wrong. Science is designed for this. Properly done it efficiently eliminates wrong answers. Of course, it not usually done completely properly. That's one good thing about it. If you don't do it right, someone else will.
@@erictaylor5462 Yes, they might simply have been playing with a toy; perhaps I gave them too much credit.
But my point (perhaps off-topic) is simple, and I stated it clearly. Ever since 1927 most physicists have agreed with the Copenhagen Interpretation (look it up if the term is unfamiliar), which enshrines mysticism in the operation of Nature in the realm of the very small. This mysticism involves many specific aspects, such as an unavoidable ambiguity between particle and wave behavior, and especially an inability to know what particular quantum state a particle or experiment is in until and unless it has been observered or measured. Some physicists have even called for a special role of human consciousness in the process of observation.
All of this mysticism goes away with the interpretation of quantum mechanics (the wave function) known as Bohmian Mechanics, which was published in Physical Review in 1952 and has since been confirmed by several experiments. It also goes away in the Many Worlds interpretation of Everett. Both of these interpretations also generalize easily in larger regimes to form the formulas of classical mechanics, such as F=ma.
Yet Bohm's work is ignored or rejected by most physicists, not based on merit, but based on history: David Bohm was falsely accused of being a Communist (because, like many intellectuals, he had attended some meetings) and as a result was barred from the Manhattan Project by Robert Oppenheimer, who explicitly asked all physicists to have nothing to do with him. Bohm left physics for awhile, learning Eastern philosophy from J. Krishnamurthi. He returned later with one final paper, which also was largely ignored.
I recommend the largely nontechnical book "Making Sense of Quantum Mechanics", by Jean Bricmont, Springer, 2016, for further information about how mysticism can be eliminated from standard quantum mechanics. There are also much more complete (and more expensive) books that present the complete mathematics and experimental evidence to back up the return to determinism that marks this interpretation.
I hope I have clarified my position to your satisfaction.
“Why dont i have any hair in that?”😹
It has to do with balance. To explain in a "hands on" sense, take a broom and balance it on your hand, counter-intuitively it's easier to balance it with the heavy side up...that's because a heavier object is more difficult to move than a lighter object...but you're controlling it not at the top side, but at the bottom. Same as the spinning disk. The demonstration on the ice removed the focal point so there was no balance due to a lack of friction, So the answer was inertia and centripetal force...and the conservation of energy. Inertia dictated how best to conserve the centripetal force.
I like your explanation
And just as a Gyroscope "Floats" above the ground "as it spins" so does the main mass of the wood....Simple. Well done jack.
exactly. But what when the hole turn downward in middle air?
I don't know how many times he did that one but I think that the disk didn't stay enough time in middle air and just turns when in contact with the ground. what do you think?
netauri123
ugstv2
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Amazing that I found this video from Zogg's rather than the other way around!
"I'm buggered if I know why." Classic.
I forget he's aussie sometimes.
Finally that bloody youtube recommend me this after 8 years
Spinning on ice is a very nice example, because it behaves differently. I suggest, that because f.ex. stone is responsible for more friction than ice, the ring once tilted doesn't actually rotate around its axis, but is rolling in a small ring and so it is changing the place of the hole. On ice, it behaves more quickly and it seems to be chaotic, because to get some friction on ice is harder.
Veritassium!!
What if you had two holes opposite one another? Would the holes be at the 3-9 position? or 12-6 position?
3-9
What if the "holes" were unequal in size (and therefore mass - or lack thereof)?
THEN IT would be very unstable at 3-9 but seems it would spin at 6 and 12
69 to be accurate
This is Gyroscopic procession, the mass if offset which will alter the area of force, as the mass spins the force location will be off axis due to the procession effect which will make it favor the lighter side, and once it's in this state it will be stable. So due to the gyroscopic procession effect the stable location isn't where the weight is, its on the other side.
3-9
spin that in a vacuum and you got the answer
+1EyeSack1 I think you mean while it is floating? It can be in a vacuum but if there is still gravity keeping it on the surface the effect will be the same.
They need one of these on the ISS.
this has been tested in the vacuum?
r u dum
why?
no air and no gravity aren't mutually exclusive. A vacuum can be here on Earth if you suck all the air out of a chamber.
We keep telling him to try it in a vacuum but he never replies.
The spinning disk differs from the tippytop, though. The tippytop has a central axis upon which to spin, keeping all of the matter evenly distributed, while the spinning disk has a hole interrupting the central axis, with matter distributed unevenly around it. The disk wobbles more as a result. Regardless of which toy is used, rotational stability matters. With more mass at the base, the center of gravity is lower, but the length of the axis above the center is greater. Axial variation is exaggerated over the longer distance and has a greater effect on rotational stability. With more mass at the top, the center of gravity is higher. The axis above the center of gravity is much smaller and insulated by the greater mass, so axial variation has less distance to be disruptive. Ice causes trouble because it undermines the stability of the axis at the base. Unlike a tippytop where the axis centers around a very small point of contact, the spinning disk has its entire circumference to use as a point of contact.
I done the experiment, and i really did not see him spin it with the whole down, but when i did it when the whole was down the disk was more stable and lasted longer. what do you mean the length of the axis above the center is greater? i am just trying to understand what is going on.
How about some controlled experiment, like mounting that thing in a bearing mounted on an adjustable axis and spin it up with a good blast of air. To go further start in a sealed chamber and then suck the air out.
I wonder. Have you tried spinning such a disc in a vacuum? I would have assumed that centripetal force was the culprit, but noticing the difference between smoother and rougher surfaces made this very interesting to me :) Thanks
I have a suggestion
Make this model on 4 different axis to form something like a ball with a hollow ball at some side
That will eliminate 2 axis factor of unbalance and a lot of other factors. If the greater mass tends to go to the top which is expected as in the toy you mentioned I guess that will totally mean inertia is the main factor.
I'm just an architect and I have no idea what I'm saying.
Architects rule!!!!!!!!! That's actually what I wanna be when I grow up. Yay for architects! xD
Translation of the large mass, Friction and floatable axis. My simple consideration.
Thank you for the high quality of videos and subjects.
I'm guessing, not completely sure, but I think maybe it has something to do with the alignment and relative positions of Centre of Gravity, Meta Centre and Centre of Buoyancy... An object when immersed into a fluid (which is air here) is under Stable Equilibrium if it's Centre of Buoyancy is below the Centre of Gravity, otherwise it will have Unstable Equilibrium and it will try to attain stable equilibrium while it can (i.e, in this case, while spinning).
Eg: An egg shaped dense object will sink into the water with it's larger side in the bottom. No matter how much you try you will not be able to make it sink down with its smaller side down... (which is quite opposite in this case... I know I'm contradicting my own statement... my physics is bad... forget you even read all this lol :P )
I discovered this phenomenon when I got my high school ring and noticed that no matter how I spun it, the heavy side always goes to the top. A ring works much better than the wooden disk because you can spin it faster, and there is no wind resistance that the wooden disc may encounter. I asked a PhD in Mechanical Engineering to explain it to me, and he said I didn't know enough physics to understand the answer.
In my opinion , i think the air through the hole is playing a major part in the transition , what do you say about it guys ?
+Aditya angara A good idea, but remember that the same thing is present in the spinning top toy, which does not have a hole for air to pass through.
+Randy Rickleman what about the fact that the spinning top's small side has less air resistance, even without the hole it has less area where air affects it.
I think the Intermediate axis theorem plays a major role
+The Physicist Cuber which also explains what happens on ice
+Aditya angara, the air not impact like for the gravity on 2 separated items, because you have only one item.
Or if the air impact on any part of the disc, it automatically balanced by the other side of axes rotation part which doesnt have a hole.
To me, it seems very similar to the situation involving a wing nut spinning (in space). When you spun the circle on ice, it seemed to favor hole up and/or hole down, but couldn't make up it's mind. So the initial flip is caused by this effect. However, friction and leverage are the "dynamic duo" creating stability when hole down. The object is resting on the bottom most point, and friction takes hold, moving the point of rotation (at least partially) from the center of mass to the point of contact. Since the center of mass is at it's furthest from the contact point in this orientation, leverage joins the party. Think of the video about gyroscopic procession, when you had a large spinning weight at the end of a 3-4ft handle. It would be much easier to change the systems orientation if you were applying force to the wheel with a short handle rather than a long one.
TLDR: Conclusion is gyroscopic procession approaching gyroscopic stability due to the magical force of gravity, friction and mechanical advantage.
I'm not sure if any other means of applying force could be used to create this stability. Magnetism perhaps, though nonferrous objects would be unaffected. Not sure how spinning metals in magnetic fields would play out either.
Watched Spinning disk trick and solution right after watching Stand-Up Maths video about spinning objects with an egg shape. Your circle is like a 2d mass simulator of egg shaped objects (although still slightly 3d I guess). I hope at least some of what i've said makes sense and is correct, and hope it helps someone to understand what we just witnessed.
"I had to investigate on my own." I'm not gonna lie....I laughed pretty hard when he said that.
My hypothesis of why the disk does the flippy thing on the ice could be because as the mass goes to the top, the disk would try roll along the plane of the disk, causing the disk to want to move like a wheel of a moving bike. When the linear motion combines with the spin, the wheel would tip and the center of mass would be vertically off-set from the point of contact with the ground and the plane of the wheel causing it to make a sharp turn every time the hole flips. Its basically like when you roll a tire of a car and then push the front of the wheel sideways, as it falls over, the friction of rolling of the tire catches the center of mass causing causing the wheel to make a really long continuous sharp turn, loose speed and eventually fall over... Basically it wasn't spun fast enough. Why that happened more frequently on the ice instead of the stone ground was most likely because its harder to keep stability on ice skates while preforming this experiment.
now what about the air that travel through the hole?? it might affect the air friction right ??
Hmmm... good question.
Wonder how it would react in a vacuum.
Also... what if it was spun (non-humanly of course) precisely vertical and perpendicular... I think you know what I mean. A precise A and B axis ? Is that what I mean ? heheheh.
sure, but he also showed the top that does the same thing, and it doesn't have any holes, implying that the air going through the hole isn't very important here.
Yeah maybe but it does affect somehow the rotational force
i did the experiment on a disk with way less surface area, and got the same results. it is more stable when the whole is on the bottom.
I think its a combination of friction and centrifugal force. The friction is constant throughout and at first causes the disc to want to wobble. Once it wobbles centrifugal force comes into play causing the larger mass at the bottom to want to move toward the out side of the rotation, and it then begins to counter act some of the friction. It stays mostly at the top because every time it wobbles off center centrifugal force increases the counter to the friction.
Isn't it the same reason that a tennis racket spins over the x-axis when you flip it over the y-axis? I thought either you, Smarter Every Day or Mark Rober made a video about that fenomenon.
I think it was Steve Mould
Two thoughts/questions for thought 1) As I recall, ice isn't really slippery: wet ice is. Ice skates slide because the intense pressure under thin blade increases the melting temperature and there is a thin film of water.....2) Is it possible that their is some gyroscopic effect difference that raises the heavier (actually the more massive) part to the top.....3) if a pin were anchored at the very bottom, and the disk is balanced (equal density board, symmetrical hole, etc.), could it be spun on its pin if spun without some "off-center-ness caused by your hand to start it off with? (why does a child's traditionally cone shaped "spinning-top" spin with its greatest mass high above its point? (good night, its too late for me)..PS thanks for your work, I find it stimulating and thought provoking.
Before I hear the answer I’m guessing that it’s because it’s center of mass is at the solid part
What an amusing video
I enjoyed it
My perception on this is that a lot of things come into play some maybe accurate or some maybe wrong yet possible to consider
Firstly we take the the circle
Of about 20cm in diameter and 10mm thick
We spin it like how we would spin a coin and it wouldn't do the switch as such
Now we take into consideration of the surface area and the balance of the object draw a half way line horizontal and vertically to give 4 sections of the circle near the edge of the circle at the end of each line we have North, East, South and West
Now if we cut a hole of centre like for example Northeast
We will affect the the spin of our circle disc
Things to consider
1-Aerodynamics
2-Resistance
3-kinetic momentum
4-surface area
5-speed of the spin
Ect......
When we take our solid disc with no of centre hole the energy is consistent until it loses the momentum
Now when we put the disc in a spin with an off centre hole everything changes yet eventually it will lose momentum it depends on how fast you spin the disc anyway back on topic by having the hole off centre the surface area is reduced and increased at the same time it has reduced by allowing air to pass through the hole creating its own drag or kinetic energy which is transfered to kinetic momentum by being of balance the hole becomes a centre point thus the increased surface area which will be where the hole isn't provides the energy to increase the kinetic momentum and eventually or quickly rotates its self round and creates uplift drag and downwards drag thus the hole be at the bottom and the solid mass near the top
I'VE WRITTEN THIS IN MY OWN WORDS TO HOW I PERSONALLY UNDERSTAND TO THINK IT WORKS NOT SAYING I'M RIGHT AND NOT SAYING I'M WRONG
IF YOUR A PHYSCIST YOU WILL UNDERSTAND WHAT I'M SAYING OR TRYING TO SAY AS I'VE WRITTEN IT IN MY OWN WORDS
i like how he finds out everything, out of curiosity and only through his effort. it's so cool
Here's what i think is happening:
As the disc spins it leans to one side and starts rolling, changing the orientation of the cut out hole from top to bottom. If you spin a coin, as it slows down it starts leaning to one side and starts rolling on the spot at a 45 degree (or so) angle, rather than spinning completely upright.
A good example in the video is at 2:28, you can see a predominant lean to one side (the side with the tape) start to develop, this causes the disc to effectively start rolling in a very tight circle and you can see that the point of contact with the ground is moving in a tight circle beneath its center of gravity.
Further evidence in the video, if you look at 2:32 the disc is upright and shows no sign of rotating over. It is only at 2:35 when the disc loses balance and starts leaning to one side that it actually starts rotating; surely if it was flipping due to inertia or centripetal force then it would start rotating immediately after it is let go?
Please share your thoughts as a comment, tell me if I'm wrong, tell me if im right.
1:55 he does looks like science
I think I understood it :).. It is kind of related to stuff like the gimbal lock phenomenon...
Firstly, the spinning forces a Gimbal Lock situation on the wheel..
Since the 'two circles' (one 'positive' and one 'negative' (a hole)) are on the same plane, they will share the rotation..
But the larger circle is 'unlocked' (you can spin it any way you want), and the smaller circle ('hole') is 'locked' (you can not spin the hole).. The rotation axis will be the same for the two circles, but for the smaller circle, the object is dislocated from its center of rotation (from the rotation axis)..
This axis offset, combined with the gimbal lock will force a Y rotation for each Z rotation angle until it is really 'locked' (the smaller circle on its most lower position).
Well, i think this is it =D...
Couldn't it be because of the "intermediate axis theorem" also known as the "tennis racket theorem"?
Rafael Caprani I'm 99% sure that it is
Rafael Caprani I
To explain why the hole moves downwards when the disk is spun in mid-air is quite easy. Consider a piece of rope hanging downwards from your fingers and make it spin along the vertical axis. It then has two equilibrium configurations: an unstable one where ik keeps hanging vertical whilst being spun and a stable one where it is swept around diagonally so that the “centrifugal force” and the gravitational force (and the tension in the rope) cancel each other.
Exactly the same is happening when you let a wooden disk hang from your fingers and make it spin. It will attempt to reach the stable diagonal configuration. As you release the disk while doing so, it will continue this motion (from vertical to diagonal) in mid-air, hence the hole will move downward (and then upward, downward, upward, etc.). So in this case, the presence of the hole in the disk is of secondary importance. Exactly the same motion (from vertical to diagonal) would happen it the disk had no hole.
You can also perform this experiment easily with a pencil hanging from your fingers. Spin it along the vertical axis and release it in mid-air. As the pencil falls, it will turn from vertical to horizontal to vertical, etc.
This reminds me of when I was younger I would take whiteout and draw a stick figure with its arms and legs stretched out on a coin and spin it and then it would look like it was doing cartwheels.
Hey,
Well I would just like to add what I think is happening. Just as you had mentioned the centre of mass lies towards the heavier side, and not at the disks centre. This is my observation one. Secondly, let us consider the clip where you drop the disk from a few inches above the ground, and still the disk behaves as before.
Now let us just talk about centre of mass (CM) and centre of gravity (CG). A body to be in a state of rest when placed on a surface, the CM and CG must coincide. IF they do not coincide, then the friction at the surface of contact, should be large enough to negate the torque created by the non coincidence of the CM and CG.
Now considering the most stable position for the disk to be, is where the heavier part being down. But that is when it is in rest. But in our experiment, the disk is rotating. And bear in mind, that the rotation causes wobbling. The first instance the disk wobbles, the CG and CM no longer coincide. This creates a torque CM. Leaving it here let us look at another piece of the rotating disk.
The base, which is in contact with the surface. here, duo to the wobbling effect of rotation, the surface experiences non uniform pattern of friction. This is true even for the rotating top, because, one edge is leading, and the other edge is trailing. The leading edge experience more friction than the trailing edge.
This change of torque duo to non coincidence of CM and CG, and the non uniform friction at the bottom, causes the disk to flip.
My guess is that, if my theory is right. If we spin the disk with enough force to sustain a spin that lasts long enough, the disk would progressively tip itself upside down over and over again.
Please do share your views on my theory.
there is also the conservation of energy here where it gains potential energy from haveing the heavy side up
But it also loses energy because of torque of friction.
Or some force does work to it.
But it obviously does lose energy duo to friction anyway.
True u do have a point man
True good point
The important thing to notice is that, once the disc is spinning upside down that torque reverts direction and creates a RESTORING FORCE that keeps this situation more stable. This stability only occurs because of dragging forces of contact. When you try that on ice, drag forces are much weaker and stability is not so promptly attained, so there may be a number of flipping before the disc eventually stops.
What would happen in micro gravity?
In micro gravity, "up" or "down" is not even there, do you think the hole will be at the bottom position? =D
well there is no bottom position in micro gravity, so no..
Alex Hall
But there would be air,,if it in the space station, so it would make for a good experiment.
7Earthsky It would be slowed down a little by air. How exciting experiment.
7Earthsky it should fly upwards wobbly, but rotating on the reverse center of travel it rolls on, I think, for the same reasons, released as upward motion. drag in reverse.
My bet is that the answer is in how you spin it. I can't work it out in my head atm (it being 1:30am) but I bet since you are spinning manually, it ends up landing at an angle. Since the center of mass is off center relative to the bottom, it applies a torque. Then like you thought, precession kicks in. The torque pulling down on the COM, starts shifting the angular momentum so that it ends up spinning around like a wheel.
My bet for the reason it stabilizes at the top is probably a combination of factors. It could be that the COM lines back up with bottom and the torque stops. Friction could factor in because after the COM stabilizes over the bottom, friction may be stopping the wheel-like rotation. Which may explain why on the ice rink it spun out of control a little bit, because friction didn't help it stabilize.
Once that rotation is stopped and it stabilizes on it's head. It could be that since it's stabilized and the COM is now centered, there any torque to spin it back to the bottom.
EDIT: Just watched the alien video. My explanation ends up similar but different. Was worried after I realized I hadn't watched it that it would nullify this comment.
I don't buy the explanations given. I've thought about this problem on and off for months. Nothing I've come up with makes sense.
However, when you form an hypothesis (friction), test it, and the test fails, you don't get to keep the hypothesis. The friction hypothesis should support a slower change with less friction, not a faster one.
This is a case where "I don't know" is a perfectly acceptable answer.
Jeff, if you want to know the true answer, stay tuned for my #AntiGravity Part 6 video. And yes you are right, "friction" is not only not the answer, the true nature of "friction" is also very misunderstood. #StayTuned
Okay, I'm just about to graduate a 2 year electrical program in Ontario, but let me try my hand at physics.
An object in motion, will stay on motion, right? So, with the disk spinning vertically in position 0 in space, nothing would happen(the hole would stay at the top).
On the ground, gravity is creating friction on the side on the ground. This will move the object's point of balance away from the point of contact from the ground (vertically speaking). Since the point of balance would be not in the center of the disk (one of the other commenters described a broom like this), as the heavy bottom of the disk moved one way, that force is reflected across the point of balance and is magnified slightly on the light end. Keep in mind that both the force of friction and the reflected forces are subject to gyroscopic procession.
If we now consider the disc to be spinning on an angle, we would see the heavy end and light end moving up and down at 45 degree angles to the horizon. Keeping in mind that the force on the light end will be greater than that on the heavy end(due to the off-center point of balance) and the heavy end has more mass, the gyroscopic procession(GP) effects are more noticeable. The heavy end will be pulled down by gravity, however GP will translate rotate that force 90 degrees. That force gets translated to the other side of the disk and amplified AND I believe that force then is affected by GP again, pulling the lighter side down more than the heavy side.
I expect that the difference between the disc and the spinning top is air pressure.
Hmm... I wonder if David Hamel's device used this principle?
For the record, this is a guess. I haven't taken any physics classes.
Solution: ehhh, not sure.
I study physics at La Sapienza University of Rome, and I had a lecture about the gyroscope (top) problem: it's all the things you mentioned put all together! Nutations, recession, friction and obviously the conservation of the inertial momentum... on ice, you eliminate the friction problem, but you have some big ass nutations because you weren't able to make it spin precisely on the axis, so i will go down but won't stay down.
found another glitch
I think the behavior in the air has a simple explanation: Your disc is asymmetric and thus has distinct moments of inertia about its 3 principal axes. Your initial spin is about the axis with the intermediate moment of inertia. This is well known to be unstable and will wobble resulting in the observed "rotations". You can check this by initially spinning the disk about the axis with the lowest moment of inertia (rotate the disc by 90 degrees and spin) and launch. Here I would expect the spinning to be stable. I would expect this effect to also influence the spinning in a surface, especially on ice, although the torque would also have to be included.
Try it by painting a spot instead of cutting out a spot and see if it still behaves the same way.
I see that most of you can't figure out how the friction actually affects the angular momentum of the disk, I'll try breaking it down so you can understand.
Let's assume that the disk is spinning clockwise. The angular momentum is pointing downwards. A torque is generated from friction due to the asymmetric spin. When Derek says that the angular momentum is decreased in the '3' direction, he means that the vertical spin(i.e. the axis along the marked line) of the disk is slowed, and in the '1,2' direction, he means that the horizontal direction(i.e. the axis along the red dots in the thumbnail) is spun up in the clockwise direction. The disk, then, turns over until it is spinning with the line horizontal.
Once the disk reaches this point, the torque is in full effect, and the torque spins up the disk along the line in the clockwise direction, and the horizontal spin is spun down by the torque, until the disk turns over. The end result is the disk spinning with its hole as close to the ground as possible.
I hope this clears up some confusion.
Actually It's Not Just Surface Friction !
The Air Has Friction Too And As Its Even More Connected To The Air The Air Force Is More Effective Than The Surface !
But The Ice Hall Is Cold More Air Molecules Are Packed So That Is Puzzling For Me :-(
Amin EnJan Why do you feel the need to capitalise every word?
Amin EnJan Ice means the surface has less friction meaning it won't be as effective
Ludvig SC Games ice has friction, a good bit actually. It's the melting water underneath created by pressure that allows us to glide through it.
Me too :-(
I wish it was the air, but i have done the experiment with a way smaller disk that has less surface area for the air to make much of a difference, and it is more stable when i spin it with the whole on the bottom. when the whole is on the top it acts strange it does not spin as long and moves the whole around more often.
Friction is a part of a solution in this experiment. Object want to keep moving where less resistance is there. Therefor any upset in the object of such formation in a proper heavy side down would mean that any change would force the object further down, and increase friction even more. In the other way, heavy side is up, and there is room to move the center of gravity down by slightly rotating, and still remaining in balance. If you spin it on perfect axis with heavy side down - it will remain that way. (from other video with iPhone spinning). In no gravity and no friction environment is would keep on spinning in exact way, as you span it in first place. Also there is gyroscopic effect, which will keep it spinning, BUT as it flips, frictions comes in full tilt. On ice (not dry ice) it would change the positions of center of gravity due to friction changing from place to place, is ice is slippery when pressure applied, and at such scale, pressure difference is massive, taking the balance out is easier for mother nature and father physics. Also on parts, where ice is already molten, no pressure needs to be applied in order to decrease friction, so it keeps on going out of balance, and you get the weird wobbly thing.
I am not sure, just got to think about it.
Other comments suggest that it might be the hole in the ring - it has nothing to do, or at least play very, very VERY VERY VERY little effect. Yes air is less dense the higher you go, but it is neglegible(i do not know how to spell it), just like 1 human in the universe, but together humans(humen?) become a power.
BOOM
THERE IS NO CENTRIFUGAL FORCE! Watch you language, it is called centripetal force. Centrifugal is your laundry machine.
Just eat cake, it's easier.
Not easier if it is spinning....LOL
I think this is actually a form of precession, and the reason is not solely the ground. If there is a hole in the upper part of the disk and you (persumably) rotate it in the slightest unblanaced way (torque and mass wise), you actually creates an imbalance with the forces (pulling it down), thus creating an effect similar to what you described with the friction. I think this is why you get that behaviour also when thrown from the air (this is also the explanation for the spinning top)
3:55 What are thoooose...
look like a pair of old Microns.
Differentiating the angular momentum with respect to time will yield a set of differential equations where the angular velocities in the horizontal plane are coupled as:
Wxdot = k*Wy*Wz + CG Offset Term prop. to y accel + X Moment
Wydot = -k*Wx*Wz + CG Offset Term prop. to x accel + Y Moment
Without the CG offset terms, the solution simply reduces to cosine and sine functions which implies neutral spin stability. Including the terms will result in two stable configurations as mentioned below.
He finally solved it in 2019... Watch the video titled something like. 'The bizzare behavior of spinning bodies '
請問您知道影片在哪裡嗎?
@whyuwhyu I have given the name of the video in the original comment, video was uploaded on Veritasium channel on 19 September 2019
i think it is that the greater mass at the bottom of the initial spin, like you said, is being acted upon by friction and torsion to push it toward the outer edge of the rotational circumference, and since the object is a solid mass it cannot travel beyond its physical boundary, so it travels upwards along that physical boundary and as it reached the top, the angular momentum of the spin is causing the mass to seek stability and that is what keep the heavier mass up top.
an interesting phenomena in space --- google "Dancing T-handle in zero-g, HD" - something similar to your ice experiment I think.
When you spin it, the wheel is NEVER COMPLETELY aligned perfectly straight up and down, which results in the weight of the wheel redistributing itself because of the force pushing the weight away from the center. When the hole reaches the bottom of the wheel, THAT IS THE FIRST TIME that weight is redistributed evenly and the weight being pushed out on both sides become's relatively equal which keeps the hole on the bottom. I've also noticed that the rate at which the hole rotates around the wheel on ice stays pretty constant. This could be because of less friction that ice has, since the wheel is not only spinning, but also rotating. It'd be like rolling a hoola-hoop backwards but throwing it in front of you. If you did it on ice, the hoola-hoop would stay in the same spot but continue to spin for a brief amount of time. just add rotation and that accounts for the Ice test. I'd love to hear your thought's on my response :)
A way to perhaps improve on this experiment could be different sized holes, I think.
I know I might not be right,but think of a spinning top. A top has a large mass spinning on a single point. However, if the top is spun upside down it won't spin for some reason. I remember as a kid I had this top that you spun rope around, and when you launched it, you would toss it upside down and pull. The top would hit the ground and then fix itself onto the metal tip on the other side. As a kid I always wondered why it had to be upside down, But if you think about it, if it's upside down then you will have a greater surface area giving it more friction with the surface it is spinning on.Then you go through the process described in the video until the spinning object finds the point at which the larger mass is at the top and the point or smaller mass is at the bottom. Basically, what I'm saying is that when an object (like the disk or a top) is spinning, the object will always try to spin on the closest thing to a point. In the case of the video, it's the lighter side of the circle. One more thing I've noticed. For the object to turn around on to the other side and spin, it must be round. The spinning top I had as a kid was rounded, so were the top and disk in the video. Think about that. I hope the people of Veritasium see this and that this helps them.
For a 13 year old, I have no idea what I'm doing here.
Ay, 14 here!! All Hail the nerds! ;)
Just in case you are wondering it's never too early. Be curious.
Still I am am 14 half and didn't get any heck
Anshul Raman
so, you say you guys are nerds... i'm 14 to, but i'm brazilian. i win hahahah
Leonardo. *too
Bro, I'm Filipino. I get the win.
It's about the two equilibria. The system favours settling into the more stable equilibrium. It's just like how a pendulum usually stops at the lowest point in its swing and not the highest possible point, even though they are both points at which the pendulum does not accelerate from gravity.
Centrifugal force is non-existent, its just an under educated persons word for inertia when in the presence of a centripetal force
That's what my physics teacher told me in high school.
In a certain way, we can say absence instead of presence...
If I tell you it exists, does that make me under educated ?
How can you say it doesn't exist when you follow that statement up with a definition of what it is? If that is what people mean by the term and it accurately describes what is going on , then by definition it does exist.
It's a common term which virtually everyone inderstands and explains the phenomenon.
I don't know why pedantic pseudo-intellectuals pretend to not understand what someone is trying to say when they use the term but they just do.
I would suggest it has to do with a fine balance between centrifugal force and angular momentum. If we consider only the motion of the center of mass (air flow through the hole doesn't matter - a non uniform disc with off center center of mass would probably behave similarly) then there are 2 different effects. Seen face front the center of mass starts from the bottom and rises up to the middle (call this, part A of the motion) then from the middle to the top (call it part B) Seen from the top part A shows the center of mass starting from the middle moving outwards which can be explained by centrifugal force. In this position however (with the disk spinning and the center of mass found in the middle - equatorial motion) the angular momentum of the center of mass is always changing (radially outwards) so the center of mass gradually rises untill the angular momentum points upwards because at this point the spin of the disk does not change the direction of the angular momentum of the center of mass.
I don't pretend to be smarter than anyone else, but I just figured this out on my own when watching the video for the 1st time :|
The reason why the disk "flips" over even when you spin it in the air is the exact same reason your cell phone flips over when you try to flip it in the "5 Fun Physics Phenomena" video - any asymmetric body will have two stable axes of rotation, and one unstable axis of rotation, depending on which principle moment of inertia is "in between" i.e. not the biggest or smallest of the 3. Because it's unstable, any slight deviation from exactly perfect initial spin will cause the disk to rotate along it's other axes, and because the center of mass isn't in the center of the disk, rotation about these other axes causes the "orientation" of where the hole is to change, If you checked that disk, you'd find that rotation about the other two axes are stable.
No idea why it's stable when you spin it on the ground though - friction seems like the best bet.
Sad I caught this video 8 years later...
This sounds a lot like something motorcycle chassis design engineers have been working with for years. Where bikes with higher center of gravity need more input to steer fast through corners and "s" bends but once enough "input" is applied, they steer faster through the 'S' bends than a bike with lower center of gravity.
While steering input can be supplemented and enhanced through mechanical means this leads to an all encompassing chaos of other factors like steering angle, trail, direction of rotating masses, tyre traction, etc.
Very interesting problem with great practical implications!
One of the only Danish physicist I've ever heard of. I'm so happy we Danish have someone to look up to.
H.C. Ørsted is the second one.
If you'll notice, when you spin a regular top that has a pointed bottom, it will move in a little circle, or wobble in place, because that point locks it to an axis. The disk and the round-bottomed top don't have that ability, because they lack a point on the bottom. Because of that they can roll over, aided by the force of their rotation and the friction of the ground. In the case of the toy that flips over, the top part has a point on it to rotate, so when it rolls over it then becomes locked to an axis and rotates around it.
I'm not sure I explained it well but that's what's happening here.
The comments about Lagrangian energy analysis have it right. Call this the principle of least action. A better example is to use a class ring as often given out in sports. They are smooth and rather spherical, but heavy at one end. With a gloss of baby oil on a glass surface, the friction is minimal and central. Spin the ring heavy end down and it will go for a long time and invert exactly once.
This is not the Dzhanibekov / tennis racket / intermediate axis effect, because it flips only once. Dzhanibekov is a mechanism in the flip, but the disk / ring becomes stable at the position with the least kinetic energy.
(Thank you, Chuck Winall (sp?) for showing this to me at Cal Tech about 50 years ago.)
I have an intuitive solution for you: Maybe, when the disc rotates, it creates a force that lifts it slightly upwards, like a helicopter. The force cannot be very large, therefore the result is just a displacement of the center of mass from the bottom to the top.
The slight angle that the disc has initially, contributes to the displacement of the center of mass, as well as the speed which it rotates.
I have not done any experiments, but off the top of head, this is it for me :)
I think it has something to do with mass trying to find an equilibrium in its constraints. The mass is being pushed away from the center, it is also attached to that central point and moves in an arch to an axis point; either up or down. When down that force is pushing against the ground causing a rebound and directing energy back up through the disc, nudging mass off axis and starts a loop. Eventually, the mass passes the mid point and will settle at the top. The mass is still being pushed up and pulled to center till energy diminishes enough for the effects of gravity overcome the influences upwards. The disc should be lighter on the scale when spinning the mass on top as compared with spinning mass on bottom, if this thought holds water.
It also makes me think of the spinning T they demo in space. How it flips back an forth. Maybe it’s the same as that, just shape not allowing for flip back down once up?
Additionally, you have that demo of the spinning mass on a rod being easy to lift in one direction and hard to lift when spinning opposite. Does rotational direction play a role in how the weight moves? Is the marker pattern different when observing?
3b. This also pushes the part of the disk with the most mass to the furthest from the axis, positioning the hole at the bottom.
Key points: A. This explains why the disk behaves strangely on ice. Without the drag of the ground, it isn't forced to stabilize its spin. B. Based on my explanation, it would flip regardless of if the hole started on the top or bottom, and would then stabilize. This would be validated if you spin the disk with the hole at the bottom, and it flips to the top.
since A is now in contact with the ground, friction would not permit it to spin all over the place.Since B has more inertia compared to A it would not behave as erratically and so the disk would be forced into some sort of 'equilibrium'. Since ice has considerably less friction then A would not be locked to the bottom. And when the disk is airborne the center of gravity of the system would move to the point farthest from the bottom as it is the most stable orientation as with anything suspended
Interesting to try different sized holes and the holes in different places. For instance, a hole in the centre - how much off of the centre does the same size hole need to be to cause the flip and various states in-between. Adding this dimension could bring in some pretty wonderful maths.
Think about this. Different angles going in same direction, and at the same time, opposite direction of themselves. If it were a clock, the rotation is 3 going where 9 is, and 9 going where 3 is. But think that 4:30 is going towards 10:30. Which is why the down right quarter is going to where the up left quarter is. But once the hole side is down, it doesnt have enough matter to balance the energy enough to go back up. That could be it. Something I just realized. On concrete, the disk stayed on the same spot. But in ice, it kept moving around. This might be why it works on concrete, and not on ice.
Note that in the spherical example the center of the ball always maintains the same distance to the floor ( r remains constant). This takes much of the confusion out of the experiment. With a disk, r can not easily be held constant.
I think it may be useful thinking of the circle as a a set of many parallel rods. So starting at the hole side up you will "build" the circle with short rods that get longer as you go up the circle until the hole, at which point it becomes broken into two sets of smaller rods until you pass the hole and the rods become long single rods again that increase size for a bit until the center of the circle and then begin decreasing to the top. Thinking like this, although more mass is above the hole when the circle spins these rods rotate and gain angular momentum. Since the wooden is of uniform density the non-hole rods will have a greater moment of interia and resist gravitys pull on either end (which would cuase rotation in plane with the circle) more than the smaller rods at the base would. The net effect being that although the rods at the base have less mass to be acted on by gravity they resist gravity less then the more massive top rods and fall to the bottom, allowing the system as a whole to come to its lowest potential.
I really love watching your videos.
That allows me to work english and sciences, and subjects you study are really interesting!
Continue to perform from that way, you're making great job
Maybe someone else has solve this already, but I believe I understand intuitively what is going on.... so let me try to explain it and see if it makes any sense.
There are several factors at play here so the best way to explain it is to break it down.
1) The disc is imperfectly weighted and so is rotating in an unstable oscillation. (it will fluctuate until it eventually finds a stable position or stops)
at certain points, the disc will oscillate violently due to the center of mass being offset from the center of geometry. (the further the offset, the more unstably it will oscillate)
so, (point 1) it will be unstable when the hole is left or right, but stable when the hole is perfectly up or down. (since it is spinning on its rim, it will get close to, but reach neither)
2) The key variable is not up or down but distance from the center mass. Instead of looking at it as "up and down"/"top and bottom", consider that the variable is actually the distance of the center of mass to the contact point (the ground). The only time gravity affects change on the object's spin is lateral friction at the point of contact with the ground.
The contact point to the ground is the main point at which unstable oscillation will inflict force to change the rotating object's path. (point 2) when the oscillation is violent and the mass is closer to the ground, the friction force applied against the object is greatest.
3) Error begets more error. The more the mass is further from the center axis, the more it will pull itself away from the center axis. so the error will accumulate and it's spin is inherently unstable.
The key to why the disc prefers "hole-down" position: When the center of mass is closest to the ground(hole-up), any minor imperfection in the oscillation applies the most direct lateral friction against the ground (the kind that would cause the disc a shift its rotation path) so any imperfection in the oscillation will accumulate until there is "sufficient error" in oscillation to violently force the center of mass off from its "somewhat" stable position to the next "somewhat" stable position. when the center of mass is furthest from the ground the effect repeats, but it can only apply a fraction of the lateral force as before. Therefore it will take longer for the unstable oscillation to accumulate enough error to cause the disc to violently flip again.
Therefore, (ignoring the infinitesimally small chance that the disc is perfectly centered (hole-up or hole-down where the lateral force is exactly zero) the condition where the disc remains for majority of its changing spin is with the center of mass furthest from the ground with equal weight on either side. (hole-down).
I believe that it's caused by the assymetrical weight distribution between each edge, one half of the disc has less mass than the other one, when you apply rotation, that causes disturbance, since it's a flat edged disc, the friction is greater so the disc finds grip to rotate harder as the disturbance in the weight distribution wobbles it up and down.
Following this line of thought, try spinning the disk starting with the hole on the bottom and see if it tends to rotate toward the top on the high friction surface (i.e. not ice). The assumption that the hole should be on the top leads him to always start spinning it with that orientation which skews the result, especially on the surface where the total number of rotations is both fairly low and fairly constant.
Take a rectangular block- say a 12"x6"x3/4" plywood. Try tossing it in the air while giving it a spin around each principle axis of inertia (those are obvious). The spin around the axis with the intermediate moment of inertial is unstable- always. The block (you can also use a book with a rubber band around it to keep it from fluttering), will remain in a stable spin around the minimum and maximum principle axes, but will always flip away when spun around the intermediate axis. This is seen in satellite motion and is a challenge when stabilizing rockets and missiles. The phenomena is part of rigid body dynamics- friction is not the reason. To understand this more, you need to look at: M = dH/dt; around the c.g. and analyze stability using control theory. You may have to linearize the differential equations for each axis's analysis (maybe not). A physicist may not be up-to-speed on the basis of classical mechanics (they are too busy doing physics using math only). Any dynamics and control professor in aerospace will explain this well. It is text book material for spacecraft attitude dynamics and for rigid body dynamics. Richard Feynman in one of his books talks about observing a dish thrown up in a cafeteria and the manner it spun as being the reason he got back into doing physics after being in a "rut" for a while. Try searching for "richard feynman and cafeteria spinning plate".
This is Gyroscopic procession, the mass if offset which will alter the area of force, as the mass spins the force location will be off axis due to the procession effect which will make it favor the lighter side, and once it's in this state it will be stable. So due to the gyroscopic procession effect the stable location isn't where the weight is, its on the other side.
Thanks for regurgitating information well known to anyone in engineering.
i think it is friction that causes it to STAY upside down, but not what makes it GO upside down. when the hole is at the top, the center of gravity is at the bottom, but it is spread out over a larger area and the top half kinda runs wild having no center of gravity to rotate around. when the hole it at the bottom, the entire weight of the disk, and the center of gravity are pushing down on the lighter side. and with more weight pushing on a smaller area, theres more friction, preventing it from wobbling like it was with the center of gravity at the bottom, and it stays there. i think centrifugal force is what causes it to wobble. with the center of gravity spread over a larger area compared to where the center of gravity is, it cant keep itself stable and begins to wobble. and when you cant go left or right or down, you have nowhere to go but up. so the heavier side makes it way to the top. once at the top, all the weight is focused to a small point when the hole is at the bottom. which gives the center of gravity something to rotate around. causing less wobble and the added friction slows, stops, and stabilizes the migration or the heavier side. i know im using laymans terms. and i know i have the right idea, just having a hard time conveying what im thinking.
I have a solution that explains all the stuff in this video and follows the laws of physics:
I would've thought that the heavy part of the disk is more susceptible to momentum and gforce therefore tries to revert itself to the position with most inertia and centripetal force which is the sides of the disk. As the heaviest part nears the side, it's gaining inertia which forces the heaviest part of the disk to keep going therefore flipping the disk, after the disk flips, the heaviest part tries to revert itself back to the position with most centripetal force(sides) and once again gains enough momentum to fully flip the disk, this happens continuously(unless it stablises from friction) or until the disk runs out of spin from the friction
I shall make 2 assumptions:
1. The force responsible for the torque is equal in magnitude and equidistant from axis of rotation.
2. The disc touches the ground at only one point.
The force being and opposite will give only torque for rotation and horizontal velocity will be zero removing any ground friction. But the center of mass will never exactly above the point of contact. Thus the gravitational force will give a torque to flip the disc. And this will again and again. So the hollow part will go up, then down, then up and so on. It matches with his result on ice surface as friction is negligible there.
I'm no physicist, but I have a theory assuming centrifugal force is relative to mass. When the disk spins, it has an imbalance. This imbalance is not caused because of the hole, but because the disk is not perfect. When the disk wobbles to one side, that side naturally becomes the side with the most mass, due to centrifugal force. Because of this, the side without the hole moves toward this point farthest from the vertex, and thus we're left with this result! Thanks!
The first word you said, "wobble" is the key. If that were perfectly balanced, spinning on a point, it would remain with the heavy half down.
Here's my two cents. The same spinning mass in a more dense gravitational pull would require more energy(to reach that state) than the same in a less dense gravitational pull. Since the whole is connected mechanically, you will find that the state with the least energy while spinning at constant at both ends would be to have the hole at the point of strongest gravitational pull. Thus, the object is merely shifting to a state of less energy.
The precession motion is due to the intermediate axis theorem. You are spinning it this way on an axis that is not maximal or minimal for the shape, which is unstable.
I think that the solution is very simple. When the center of mass is above (with respect to the center of the earth that is pulling down the whole thing due to gravitational forces) the center of the circle, the force tends to align the edge of spinning to the edge of symmetry. When, the center of mass is below, the forces tend to "anti"-align the edge of spinning to the edge of symmetry in the disk. Here, the edge of symmetry is the line crossing both centers, the center of the big circle, and the center of the small circle or hole.
Wouldn't the relationship between angular momentum and density have something to do with the answer? When you start spinning the disk in the air, the side with the hole is pulled in the direction of the force more quickly than the rest of the disk because it has lower density and therefore a smaller moment of inertia.
Friction then plays a part when the disk is on the ground, as seen in the differences between the ice and the concrete. But when the ground is in play, you are also including the normal force of the ground in the sum of all forces. With no angular momentum, the side of higher density will want to be pulled toward the ground.
The further from the center of gravity the bottom of the disk is horizontally, the greater the torque that the normal force plays on the disk. On concrete, friction is preventing the disk from slipping too far from x-y equilibrium, but on ice, there is less friction, and a higher tendency for the base to move away from the center of gravity and create a rotational moment about the centroid.
Angular momentum pushes the hole downward, torque from the normal force pushes the hole upward. With a long enough moment arm, or a small enough angular momentum, the hole will fight its way back to the top. Otherwise, the hole will be pulled to the ground.
It is about moment of a force. Imagine two sticks in a T shaped configuration. The upper left point is point A, the upper right one is B, the bottom one is C and the intersection is D.
The distance between point A and D is equal to x ,the distance between point B and D it is equal y, and x = y. The distance between points C and D is equal h. If we put 50kg at point A and 51kg at point B, the only way to maintain it in equilibrium is spinning it. There is two reaction forces at the point that is in contact with the ground, point D: the normal force direct upward, equal to g*(50kg + 51kg). And the reaction (F = F1 + F2) caused by the moment of forces: g*(50kg)*x = -F1*h and the moment of force reaction in the opposite direction: g*(51kg)*y = F2*h.
That reaction force F caused by the moment of force is also present at point C an it is parallel the the stick AB. That is the force that destabilize and that is why we spin it to maintain it in equilibrium. So when we increase h, F is consequently reduced and the sistem is more stable. In the spinning disk situation, when the hole goes downward it means that h was increased and F reduced. At the ice situation, there is almost no frictional force to react the moment and produce F.
At the free fall situation, I think that the hole just turns downwards when the disk hits the ground. But, if the hole really turn downwards in middle air, the only possible exlanation I can think is about the difference in the center of mass and the center of gravity or some diferences in air pressure and air resistance. Sorry for the bad english.
It's moment of inertia. Because there is a difference in mass and the object is symmetrical, less energy is required to spin the hollow side, but "spin" energy must be balanced due to it's geometry, this causes it to move across the axis. I'd wager is you make two holes in the disk that are on the same axis the disc will spin with the holes in the middle.
I'd say it's the same reason why a rotating wheel (like on a bike) tends to stay locked in a position regardless of where the center mass is. Imo it turns upside down because it's easier for the heavier part to stay locked in place by disc's rotation on top and the fact that the bottom side is touching the ground makes it less likely to "wander off". If it was the other way around then the lighter part is more likely to wobble off the center because it doesn't have as much mass to keep it in place just because of the rotation and the top part of the disc is always more likely wobble than the bottom part because of the contact with the ground.
The disk is turning to a stable equilibrium. When the hole is at the top small changes in the spin massively change the inertial pattern. Once at the bottom the disk is at an equilibrium and the friction pushes it back and forth. On the ice (ie with out friction) it will still rotate down but like a spring it will pass it's intended location.