What IS Angular Momentum?
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- เผยแพร่เมื่อ 18 พ.ย. 2024
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
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"It works, even when you try to break it" - This should be Nokia's slogan
:p
I wanna like this comment but it has 420 likes
I see xd
😂
Hiya
Angular momentum: How much "umph" an object has when rotating an object.
+Dami Bang What is "umph"?
umph: strenght or energy.
i was quoting him.
+Dami Bang umm. impulse?
Oumph is food to me haha
BoggyBolt oompf sounds more fun.
"It works, even when you try to break it."
And then there was Quantum.
LeiosOS omg I saw this comment when he said it XD
It works, unless you check if it works
To be fair, you can't know if you're breaking laws if you don't know exactly what they are.
Ooooo daammnnn
LeiosOS bbh
"so, what exactly is spin?"
- every physics student at some point
I understood that reference (I think)
@@huepjr5606 my boi andrew
It's the Seljurk Turks
Aah!
The Spin is a state of rotation defined by its closeness to perfection, that perfection being the Golden Rectangle (黄金長方形 Ōgon Chōhōkei), more specifically the Golden Spiral that is derived from the Rectangle, a mathematically endless spiral, and a feature said to be omnipresent in the surrounding nature and a fortiori in works of arts.
Something you measure.
My teacher tried to explain this and I didn't understand it. Now I do, thanks to you!
mine never did but i knew from studying my turd flushing down the toilet
My teacher did not even teach it!
Make that two cookies.
***** Cookies incoming!..
2:03 ... size of the wheel should tap the radius not the diameter.. it should have been 0.3 as the formula stated..F= m*r*v.
Quantum Mechanics:
"It breaks, even when you try to make it work"
i need a minutephysics channel for chemistry
minutechemistry
@@macaroon_nuggets8008 oo wow
try Professor Dave Explains
"Physics, it works even when you try to break it"
It's still a bit confusing but you explained it a million times easier than my professor in college. Thank you for the video. I learned something!
1:17 "yup i messed up diameter and radius"....
like as if anyone even noticed that mistake.
Rick Sanchez 137-C I did
came to cmnt the same lol
#metoo
no mistake. a bike wheel is both translating and rotating. if you did L = m*r*v you would only get the angular momentum because of the horizontally moving center of mass. you also need to account for the fact that the wheel is spinning, which you do by multiplying the moment of inertia of the center of the wheel, m*r*r, with the wheel's angular velocity, V/r. the total angular momentum is:
L = m*r*v + m*r*r*V/r = 2*m*r*v = m*d*v
scripts.mit.edu/~srayyan/PERwiki/index.php?title=Module_3_--_Angular_Momentum_of_a_Rigid_Body_both_Rotating_and_Translating
@@silkius809 are you sure about that, your first term "MVR" is for linear momentum of the center of mass wrt to a reference point, the second part is correct, however we can't add them as the "R" in the first term depends on your reference point
Why dont they teach physics like this in schools? Its so easy to understand without all the intervening gobbledegook.
+Red .Rotten Totally agree with you. What I also HATE is they take all the calculus out of physics. U need calculus to link so many concepts, deal with curvilinear motion and for efficient calculation.
+Red .Rotten I completely agree. The answer is that schools are drowning in dogma and are completely lacking in creativity.
Because you still can't calculate how two bodies with specific velocity at a specific distance from the sun will interact with each when they collide, assuming zero elasticity.
Because audible doesn't sponsor our education
Yet.....
For the cycle wheel you took diameter as radius you were supposed to divide the diameter by 2. Then the answer would be around 3.5 kg.m²/s. I hope that makes sense to you!
study physics for years and you realize you cant even visualize angular momentum yet
+Shrey Joshi thats becouse you don't have creativity :3
No it is cause it is not a physical phenomenon it is a human made thing to understand something like, mathematics
Mathematics is just a language used to describe the universe and physics. In a way it is discovered not invented. Creativity does have great impact in discovering new ways to describe something
Play Kerbal Space Program. See how orbits behave, particularly hyperbolic escape trajectories. Realize a game about freaking green men exploding rockets and thinking observing goo is "science" just helped you visualize angular momentum. :p
Lots of amateur physicists here. I know what you mean, the more you study physics, if you don't start to question everything you know you aren't doing it quite right. To those people say you don't have enough creativity... tell them they don't have enough physics hahaha
This was an interesting video. I really liked how you guys included many examples, it really helps.
It's L because it's _angular_ momentum. L looks like a 90º angle.
Holy shit
I was coming down to comment this. But you beat me by 3 years.
Is your pfp Lance? Do you play EBF?
Is that the real reason it uses L?
Because if so it makes me unreasonable angry
So then what about torque
My first year physics courses covered this. It took me a while to really grasp how exactly it worked. I had knowledge of it, but not quite understanding.
This quick video explained it in a way which makes me feel like I finally have some firm understanding of what angular momentum is.
Thanks Henry for these videos! I stumbled upon your channel during my senior year in high school, and because of you, I am a 3rd year undergrad Astrophysics major.
What was this video about again? Something about circles?
I believe it's a warning about the fact that the sun can disappear at any time!?! I'm now terrified.
It was about tities.
cuellartovar That's one valid conclusion sir. Now alI orbits look like tities to me. Just great! as if I didn't need more distractions!
cuellartovar hepatities
PlagueOfGripes Wait, plague? Shouldn't you be learning about this by watching a cat on a record player or something?
This is a very good video, Henry. I did learn about angular momentum in college and how to use it solve rotational mechanics problems but I never quite realised the practical implications of its conservation in the way you showed. I think that is the point of watching Minute Physics, to grasp the way concepts and laws of physics can be explained and visualised in interesting ways I wouldn't have thought, at least for me. Thank you.
You just explained the concept in just 3 minutes which I tried to understand for more than 1 hour
Thanks for the video❤️
F=dP/dt (Newton's Second Law for Translational Motion)
τ=dL/dt (Newton's Second Law for Rotational Motion)
in case anyone was interested.
Well, who would have thought that if you take Newton's second law and you multiply a vector on each side, you also get an equation.
This is just useless verysmarting. If someone doesn’t understand it, it’s useless, and if they do, it’s trivial.
Ben Stankovich agreed
@@---kp1hm agreed
How simple, effective and just plain precise this video is. Thanks.
I was having trouble with this concept and I have a test on it tomorrow. Then in French class, my phone buzzed, and there it was: "minutephysics has uploaded a video: "What IS Angular Momentum?"" Thank you Henry.
One question though, with your wheel example around 1:10, aren't you supposed to divide the diameter in half?
M CP Yes you are, if you turn on annotations he corrects this error.
Natasha Taylor Alright, thank you :) yea, I'm watching on a mobile device, so I don't have annotations. I saw people talking about it in the comments below mine though. Thanks again ;)
This is the first description of angular momentum that has truly made sense to me. Thank you!
If it is 0,6 m, then wouldn't you have to multiply by 0,3m (it's radius)? Or did you spell it wrong in the L= thing?
You are correct, there was an annotation in the video where he points this out.
critical7world Damn, I tend to miss important stuff like that because I, like most, keep annotations disabled by default.
critical7world retepsemaj96 Yeah, he added it after the video, which i didn't see.
gta4szakis Also, fun fact: the earth has an angular momentum of 7,71428571*10^39 (!!!), not 3,85714286*10^39 bicycle wheels.
patu8010 Why?
L comes from the "right hand rule" of vector cross products r x p=L. Since r and p are in the x-y plane, they are perpendicular to each other and form an "L" shape
Any idea why theta is commonly used for angles? Neither angle (ankulos) nor corner (gonia) start with a theta or even have a theta in their name, in the Greek translations. Makes sense for alpha and gamma to identify angles, but theta seems to be completely arbitrary.
Perhaps it is like x, y, and z being used for coordinate axes. Letters selected precisely so that it is unlikely they stand for anything in particular.
Nice, just learnt this before I got to it in highschool - always good to be a step ahead and to have a little more physics knowledge in your pocket.
Thanks!
I agree. If you already know something about the topic, you can understand way more when it is presented in University/highschool
In case anyone missed it, there is a great illustration of Kepler's 2nd law at 2:35, which deserves a video of it's own.
Am I only the one who noticed, that at 1:15 , since the diameter is 0.6 m and you need the radius for calculating the angular momentum, the solution should be around 3.4 kg*m^2/s instead of 7? Or am I missing something?
I'm taking both art lesson and learning about physics at same time. You're a great explainer.
"It works, even when you try to break it."
Well clearly this guy needs to play more video games.
That rap about circular motion at the beginning was everything.
Can somebody explain, what is the difference between momentum and kinetic energy (both linear). I know the formulas are different, but what does it really mean?
That's a good question.
Well, by definition (and because of conservation of energy), kinetic energy is the work needed to accelerate a certain object from rest to its actual speed (which defines kinetic energy 0.5*m*v^2)
Imagine 2 baseballs, with the same linear momentum (defined as m.v where m is the mass). One ball A with mass m and speed v, and other B with mass 0.5m and speed 2v.
Clearly, the ball B has more kinetic energy (the double of ball A), but the same linear momentum.
If you were to catch these 2 balls (with the same deaccelerating force) what would the difference be?
Well, since both balls have equal linear momentum (also defined as F.t where t is the period of time time in which the force was applied), it will take you the same amount of time to fully catch them and put them to rest.
BUT, here is the main difference: since the kinetic energy as said above is the work needed to accelerate (or deaccelerate in this case) a certain object to a certain speed, and work is defined by F.d where d is the distance in which the force was applied, the ball B will take your hand twice as back from your chest, since it has twice the kinetic energy of ball A.
Apart of those 2 things (definition and consequenses), I don't think there are any other differences. If you are good at math or algebra you can see it for yourself by trying to proof this (it's not that hard).
I hope this helps you out!
Energy=Fd=dma=dmv/t=d^2 m/t^2
Momentum=mv=dm/t
Energy/Momentum=d^2mt^-2/dmt^-1
One of the distances cancel out, one of the times cancel out. Mass cancels out.
E/M=dt^-1=d/t=v
The difference between energy and momentum is velocity.
There are a couple of other important differences beyond what Fede Aguilera already stated. First, momentum is a vector; so, when we talk about momentum, it's not just about how much an object has, but also the direction in which an object is moving. This is particularly important when considering collections of objects, as the magnitude of a sum of vectors is usually smaller than the sums of the magnitudes of those same vectors. In fact, the total momentum of a system of moving objects can even be 0.
Energy, on the other hand, is a scalar; so, it does not have any direction associated with it. This means that energies always add directly. And, when accounting for energy, it is necessary to consider _all_ types of energy, not just kinetic energy. This is because energy can change forms. For instance, if two balls of wet clay slam into each other and stop moving, the kinetic energy they started out with ends turns into some combination of potential energy (holding the resulting clay ball together) and heat.
On a more technical note, there is a theorem (called Nöther's Theorem) which states that there is a one-to-one correspondence between conservation laws and dynamical symmetries. Through this, it can be shown that momentum is conserved in a system if and only if the dynamical laws governing that system are translation invariant - that is, the laws are the same in all places. And, energy is conserved in a system if and only if the dynamical law governing the system are time-translation invariant - that is, not changing over time.
Finally, I'll note that in relativity, where space and time are not separate but, rather, form a 4 dimensional spacetime, energy relates to momentum in exactly the same way that time does to space.
***** You are not.
Parlyne NIce, I couldn't have thought of that, and didn't know some things, Seems like you can always learn something new about something you already know!
Fede Aguilera Glad to be of service.
this is the first explanation of angular momentum I've honestly understood other than accepting physical formulae. thanks. this is great.
Awesome video MinutePhysics! You explained it vey well (albeit still very fast). xD
I think I heard somewhere you majored in physics? What are you doing now?
SPNKring Yes, I'm the insane person who majors in physics and minors in math. xD
What are you career plans? Are you working?
SPNKring No work as of now, and career plans are still on the undecided side. Still looking into stuff :)
Well, good luck in the future!
As a feller just taking a physics course for the first time, this video is fantastic. We haven't even covered this topic, but I see how it relates to the other stuff in the course like momentum and circular motion.
Why's there always a fucking cat?
+Sejal Yadav because cats are cats, and u have nthing to deal with that. :)
Its a reference to schrödingers cat
Why? Because of this! lol www.popsci.com/research-shows-cats-may-understand-cause-and-effect
Why not?
Schrodingers kitty
2:24 exactly what I was looking for. You're gold.
The more physics you learn less And less sense it make
This makes sense to me. What part confuses you?
Think about spinning a ball on a string. You have the speed you are spinning it, but it can't go straight. Once you let go, the speed stays the same, but the ball goes straight instead of a circle.
Excellent explanation!
I especially admire how your illustrator avoids the common intellectual trap of showing electrons in idealized Newtonian orbits. Instead he draws a randomized chaotic "cloud" of potential particular positions. (0:24 and 0:32 [center]) Even though it's impossible to draw such things to scale, the idea of probabilistic "orbitals" (as opposed to orbits) is conveyed more accurately than illustrations of the past.
Near the end, you show how angular momentum is conserved even if the central axis (the Sun) is absent and the Earth travels in a straight line. (2:24)
That would be a great primer lesson to help students understand Kepler's 2nd law: How planets sweep equal areas over equal times regardless of position or speed in elliptical orbits.
The principle is the same for elliptical orbits and the diminishing area of triangles seen in this straight-line example.
If you have NOT already shown Kepler's laws, then I might suggest doing them next.
If you've already done Kepler's laws, please consider linking that video to this one.
Also admirable is how you use simple common words like "stuff" or "oomph" instead of matter or momentum. Using the little gift-wrapped box is user-friendly too. Very clever and fun!
Great Content! Please keep up this valuable important work!
Doesn't this mean no one is going anywhere? Everyone has their "own circle" that they go nowhere in. I'll never leave the earth, the earth will never leave the sun's orbit, the solar system will never leave the galaxy, and the galaxy will go where ever it's going, but probably in its "own circle", and so on. It just sort of seems this "going nowhere" is relative, and basically everything is going somewhere and nowhere at the same time.
Schrodinger's circle! ahaha nvm...
Yeah, in the grand scheme of things going to the moon and existing in general aren't very big accomplishments that's why I avoid the grand scheme at all costs.
No. He picked the point of the Sun, put you can pick any arbitrary point. That means the an infinite number of imaginary circular paths. It has nothing to do with the objects actual path. It's just saying that if you were to tie an object or group of objects to a pivot and measure the torque impulse, it will be the same no matter when you do it.
JWQweqOPDH Oh, I see.
What I've always wondered is how the various angular momentums (me relative to the earth, me on the earth relative to the sun, me in this solar system relative to the Milky-way, me in the Milky-way relative to the expanding universe) interact with each other. Is there ever a time when, taken all together, we are actually standing still?
MakeMeThinkAgain Yes, there is. You just have to take a reference point such that the object(s) in question are moving such that they will not pass through the reference point (this creates an angular momentum in one direction), and have it such that the side of the system of objects closer to the reference point is moving faster (in the direction of the object) than the side farther away (creating an angular momentum in the other direction). Play around and there's a point where the angular momentum is zero. This means that if there was a black hole at the reference point that was not spinning to begin with, if all the objects in question fell in, the black hole still would not be spinning (ignoring any ejections from the black hole). In a similar fashion, if they collide with any object anywhere else, the angular momentum of everything will be the same before and after the collision, if you keep the same reference point.
I LOOOVE the atom animation at 0:28!!!
Awesome video!!!
Why is angular momentum written as " *L* "
It's to do with vector cross products, the radius and momentum vectors are perpendicular to one another and so form an L shape.
Well explained. 👍
Floobs I'd say it's actually an arbitrary selection, and even if it was not it's probably closer to "AnguLus" than to the cross product.
You know, the L from... Le angular momentum.
For the same reason momentum is P. Because fuck you.
I do like how you can describe a lot of things as simply or as complicated as you want by simply changing the geometric references.
Very good video. Nice channel.
I like that, although these videos are almost by definition as short as possible, he still goes to the trouble of listing as many synonyms of spin as possible.
My Physics teacher would be ashamed after watching this video.
Thanks Henry. I understand Angular momentum now!
"That's the beauty of a law of physics.: It works. Even when you try to break it"
"I'm going to BREAK you, physics!!"
"Pfff, lol, I'm physics, you can't break me."
This is the type of videos I subscribed to Minute Physics for.
"That's the beauty of a law of physics.
It works. Even if you try to break it."
I can see how many people didn't get this video, but I got it. Thanks minute physics! Glad to see you back making videos after such a long hiatus.
Hey, mechatronics engineering student here. This video isn't completely accurate and correct. They are mixing product and cross product. This has A HUGE impact on what they said of the Earth rotating around the Sun- because its trajectory is an ellipse, not a perfect circle. *There is a fun fact about the conservation of the angular momentum hiding in there which explains the Earth's moving speed*. Here's a short, simple explanation in 5 steps (skip to 5- main part if you don't feel like reading much or you don't seek an explanation because you already know the basics):
1) Position and velocity
*Position of an object* (r) *is* presented by *a vector* (for instance- in Cartesian coordinate system- it has 3 dimensions according to X, Y and Z axis... or in Polar coordinate system which is generally used for object with trajectory within a plane- its dimension is 2).
*Velocity is* defined as *a derivative* of the position vector with respect to time, thus it is *a vector* as well (dr / dt).
2) Difference between scalar and vector
Momentum is defined as a product of mass (which is scalar) and velocity (which is vector), and scalar and vector cannot be multiplied as a cross product. Cross product is defined ONLY with vectors, and it looks like:
vector1 *x* vector2 *=* intensity_vector1 (scalar) • intensity_vector2 (scalar) • sin(angle between vector1 and vector2)
and it represents another vector, orthogonal to plane built by vector1 and vector2.
You CANNOT multiply *scalar* (mass) *x* *vector* (velocity) because angle is defined only between two vectors, scalar is not defined in vector space.
3) Momentum
Soooo... due to this, you can write momentum only as mass • velocity, so it is a vector itself:
mass (scalar) • velocity (vector) = momentum (vector)
m • V = K
4) Angular momentum
Angular momentum is defined as a cross product of a *referent position vector* (we take the Sun as the reference) and momentum:
*r* (position- vector) *x* *k* (momentum- vector)
......or:
r *x* k *=* L
......or:
r *x* (m • V) *=* L
......or:
m • (r *x* V) *=* L
.....or:
*m • r • V • sin(angle r, V) = L*
5) Fun fact
If the Earth's trajectory is an ellipse, and its velocity has a tangential direction on that ellipse- then there are ONLY FOUR CASES
when angular momentum equals exactly *m • r • V*, and that is when the angle between position vector and velocity equals 90 degrees because sin(90) = 1, or:
L = m • r • V • sin(90) = m • r • V • 1 = m • r • V
Those four cases are: two when the Earth is furthest, two when the Earth is closest to the Sun (just look at the image of an ellipse and you'll easily see it).
THE MAIN PART: *if* the *angular momentum* of the Earth *is constant*, *and* if we take the *mass* as *constant* (even if the Earth's mass slightly changes dues to stardust, gasses being blown away or brought by solar winds, etc)- and if we conclude that *sin(r,V) • r is NOT CONSTANT* (it takes some geometry and mechanics calculations to prove)- then what effect does it have to *the velocity???*
L (constant) = *sin(r,V) • r* (non-constant) • m (we take as constant) • V (is it constant?)
Logical conclusion brings that the *velocity's intensity* MUST *NOT* BE *CONSTANT* because it has to negate the changing *sin(r,V) • r* influence (in order for L to be constant). When sin(r,V) • r is decreasing- velocity increases, when sin(r,V) • r is increasing- velocity decreases- and only this way the angular momentum remains the same, remains constant.
This is a mechanical explanation why the *Earth increases its speed when it moves closer to the sun*- *and* why *it slows down when moving away*. Earth's speed would be constant if its trajectory was a perfect circle- or if it crashed into the Sun and remained there (r = 0 *=>* L = 0 = constant).
Thanks for reading, oh, and sorry for my poor English language knowledge/ typing mistakes :)
If you watch the video again, you may note that he's talking about v as the tangential velocity wrt the reference point. That is entirely (and even technically) correct. Just because cross products in 3 dimensions have the nice property of implicitly calculating that, they're in no way, shape or form needed.
Yes, the tangential velocity of the earth moving on its elliptical path isn't constant. (Actually the velocity in its entirety isn't constant either but that's conservation of Energy, not of angular momentum).
This mechanic has, by the way, nothing to do with the earth increasing in speed when getting nearer to the sun. It predicts that a bigger part of the earth's velocity will be in tangent directions as opposed to radial directions. Imagine an object moving in a straight line past a reference point in space. The radius decreases as the object gets closer, but the velocity of the object won't change, only the tangential component will become a bigger part of the complete velocity.
The reason the earth speeds up as it nears the sun is conservation of Energy. The potential Energy of the sun's gravitational field is transformed into kinetic energy of the earth (and the other way round on the path away from the sun)
Hope I could clarify
PS: In this video L is defined as a scalar value, what you might call |L|. As you use them interchangeably in your calculations (note how the last line in (4) is a vector tangential to V and the line above is perpendicular; the last is only equal to L in length), this shouldn't be a problem. In fact, as L is an invariant, so is |L| obviously. Also it's way easier to visualize (As in the vid)
OOobstkuchenOO Thank you for the reply! Yeah, I know, I haven't dealt with scalar/ vector markings while typing yet, it's difficult to mark. Also, I should have dragged the unit_vector orthogonal on the plane built by vector *r* and *V* through all the equations after I've stopped using the *r* x *V*, but I accidentally left it out because I considered that L's direction was already defined so I was marking it as a scalar, or
L_vec = L_scal • unit_vector
....
so, I had it defined:
*L • unit_vector* *= m • r • V* *• sin(angle r, V) • unit_vector* /// divide all by unit_vector, so you get:
L = m • r • V • sin(angle r, V)
>>> and this is still not the same like in the video, in case the trajectory is not a perfect circle where angle r, V = 90 deg (or 270 deg if you want a different direction angular momentum).
Also, I totally agree that the cause of intensity increase/ decrease in Earth's velocity is due to potential energy being converted into kinetic and vice versa, but every change in an object's energy is described as work- and work describes force that makes the object's move on a certain part of the trajectory.
That work can be introduced into simple mechanical equations by:
mass • a_vec (acceleration) = F_vec
mass • (d(V_vec)/ dt) = F_vec //we multiply all by d(r_vec) and get:
mass • d(V_vec) • (d(r_vec)/ dt) = F_vec • d(r_vec)
where
F_vec • d(r_vec) is the work (marked by W or A) so you get:
*dEk = dA*
and when you apply integrals, you get:
delta_Ek = A // or // Ek2 - Ek1 = A
Meaning that the change of object's kinetic energy is resulted by the work- which further means that the Earth does that work while traveling on its trajectory. Every work is followed by the change of object's mechanical attributes- in case it's not the zero work.
So- there might be a major change in the ratio of Earth's normal and tangential acceleration- despite that their sum stays the same- but that still has effects on the velocity (its intensity).
So you can prove the change in Earth's velocity either through kinetic energy and work (the harder way) or the angular momentum (easier way)- it's your call.
You guys just hurt my brain. lol
AlphaArcticWolf hey, freshman mechatronics engineering student here. Where do you study?
Ricardo Espinoza Faculty of Technical Sciences, Novi Sad. Our mechanical studies span over 3 semesters and our studies are based on German and Russian mechanical approach. We use literature from Kolesnikov to practice how to apply theory (not sure if you can find the book online).
Our education program is set like this:
Mechanics 1- Newtonian mechanics, practice of integral and differential equations in mechanics, Coriolis force, systems in balance, etc
Mechanics 2- virtual movement, virtual work, Kane's equations, Gauss principle, Gibbs- Appell equations and many others.
Mechanics 3- I get to choose whether I want this subject or the "machine mechanics" (something like applied mechanics)... idk.
We also have the material resistance which is something like "material mechanics".
I must say I'm not a specialist in mechanics, but some basic principles should be understood.
Conservation of angular momentum is great. I was part of a really neat demonstration in first-year physics where I sat on a rotatable stool, and was given a heavy, horizontal wheel which was spinning on a bar. Once it entered the system of me and the chair, if I tried to slow the wheel, I would suddenly start spinning, because the angular momentum would transfer to me. It was surreal and nonintuitive.
There's also that lovely xkcd comic about spinning with the world to slow it's turn by negating its angular momentum.
I learned that the Earth's momentum is 4000 quintillion quintillion bicycle wheels.
Now that's an explanation I can wrap my head around! Thanks for the awesome video.
1:17 why did you multiply by 0.6m, the diameter rather than the radius, 0.3m?
+Blake Bernard my physics lecturer has drilled it into my skull! (And unit errors)
He didn't he just showed the diameter not radius
this is {comma} by far {comma} my favorite explanation of angular momentum ever {exclamation-mark}
Why is it L? I really don't know
lmomentum
Maybe because it was originally meant to mean angle, but later became 'L'. (Because 'L' looks sorta like a 90 degree angle)
Because every other logical choice to call it, was already spoken-for in classical mechanics. The L looks like the two perpendicular vectors of radius and momentum, so that's why it was chosen.
The p for linear momentum was selected from the word impetus. Another instance where m is already spoken-for to stand for mass.
I think that this might be one of the best videos on this channel
Someone needs to make 10 minute physics and actually explain things without talking like one of those terms and conditions guys at the end of promotional adverts. This entire channel is such a great example of wasted potential. The amount of people I could post this shit to rather than explain things in detail - but I can't because he prattles too fast.
One of my favorite Minute Physics videos to date.
Earth doesn’t know anything about the momentum, so it goes ahead and flies anyway.
Angular momentum by electro-magnetism or gravity is a beautiful thing in physics. :)
I guess the part where you remove the Sun would be easier to understand for some people if you explicitly mention the velocity along the circle and draw dots on the intersection between those lines and the circle so that people will see the distance traveled along the circle decreases as the Earth moves away from the original circle. The best way to see this is to keep looking at the original circle so you will see that the angle traveled per time unit decreases as the Earth moves away. Then it is clear that the speed on that now-imaginary trajectory of the circle decreases. Still a very clear explanation. I love your channel. Keep up the great work in making people understand physics and raising interest for it!
One question though... how do you READ an audiobook?
synaesthetically
oh wow. If my plane trigonometry teacher was this interesting....well, if any of my teachers were this interesting...hmm. I forgot where I was going with this.
Well, anyway, well explained dude, thumbs up.
And then quantum particles come along and they're like "Look at all these laws I don't respect"
They still follow conservation of angular momentum. Although it's harder to figure out what that is given that they're more like ripples than billiard balls.
+blacklistnr1 *cough* spin *cough*
i think it's better to point out that L is a vector product of momentum and radius , since a vector product in this case p times r times sinx , where x is the angle between p and r.
so even if the distance between the rotating object and the refference changes, sinx also changes to keep the vector product balanced and conserved.
angular momentum is truely one of the most brilliant things we have in physics, it allows you to calculate everything from planetary orbits to the energy levels of multielectron atoms with great precision
in fact, the vector model of the atom is still one of the most succesful models of atoms, considering it is a pre-wave model.
+sidewaysfcs0718 It's only better to point it out if we can assume the viewer knows what a "vector product" is. Probably not, and then also this necessitates a directional component that wasn't useful in the context of the illustrations.
This is a pointless comment.
This is a pointless response.
Victor G Both of your comments do have a dot, however, my comment does not
mrBorkD There is a point on your 'i'
This is a pointless game.
.
I've realised that your videos are more for people who already understand the subject of the video and this helps clarify small questions, rather than someone who has little to no knowledge. I felt lile twista was lecturing me ;_;
The laws of physics are generated by God, who is able to impart a reliable and constant facet to our universe. No other worldview predicts that laws of physics should exist.
nice b8 m8 I r8 8/8
You need to stop posting religious comments on MinutePhysics's videos. I respect your opinion and right to believe, but please don't comment on videos that have nothing to do with it. You are doing nothing but creating heated arguments. Trust me, hateful replies will come soon. Sincerely, a fellow christian.
I don't mind u posting religious comments. As long as u don't force us into believing by killing people, burning witches, beheadings, ...
***** it was obviously bait for someone like you
Andrew white is not so bright
There a rhyme for you, you poor soul who is afraid of opening it's mind
I'm an engineering student and these videos actually really help!!
I love the ending of the video: ''Thats the beauty of a law of physics. Even when you try to break it. It works''
your way of teaching is amazing
I like this. Angular momentum = thing circling around a point.
Angular momentum = thing moving straight forward, just with smaller and smaller angle to a certain point :)
for those of you confused:
L=vmr=(30e3 m/s)(6e24 kg)(1.5e11 m)=2.7e40 kg*m^2/s
if you are not given the tangential speed (v) of Earth around the sun, use Earth's radial speed (ω):
to find ω, we use the orbital period of Earth, which is T=365 days= 3.2e7 seconds
find the frequency f=1/T= 3.1e-8 rev/s
ω=2πf=1.96e-7 rad/s (**you can now find the tangential speed v by using v=Rω...v=3e4 m/s=30 km/s)
Now use L=Iω to find the angular momentum where I is the moment of inertia of Earth
I=(2/5)mR^2 because we're pretending Earth is a uniform sphere, with it's center of mass directly in the center, in the center of it's axis of rotation (I=(2/5)mR^2 is the equation for a uniform sphere, because of the way we integrate the maximum perpendicular square distance from the axis of rotation (R), from the center of mass, ∫(R^2)dm)
L=(2/5)(6e24 kg)(1.5e11 m)^2(1.96e-7 rad/s)
L=2.7e40 kg*m^2/s
now this, is a pointless comment
+TripedalTroductions holy cow that made me even more confused
ill get u back
I learn better this way than in school, the visuals help allot.
Well done! Have seen a number of explanations, but none better or quicker than your description.
I really love his art style!
Unlike every other video I watch on TH-cam, on yours i have to stay so damn focused
tertiary education - numerous lessons on angular momentum, and still a bicycle staying upright is something I can't explain.
CyberPsyLen That's okay, there's been papers being spouted out for years arguing about how it works. I believe it's now accepted that it has something to do with corrections provided by a trailing wheel, but I honestly can't remember. It's not due to angular momentum though - they tested it by putting flywheels on bicycle wheels to counteract the angular momentum and found them just as easy to balance.
Who dislikes these beautiful videos?
Just saw a short yt clip nd i was BLOWN AWAY,
Every video of yours blows my mind a little more
Thank you... Our hard to understand physics teacher can't teach but now I'll pass. More of things like this please.
Finally a new video! I'v been carving them since school stopped...
That was the best representation I've ever seen of an electrons motion in an atom!
we literally did this today in class and i was kinda confused thx i love this channel
as someone who didn't understand angular momentum when I learned it in physics late semester, thank you!
That last sentence was gold
That was a great demonstration! I used to teach atmospheric physics to budding meteorologists and I wish I'd had this video to show them.
Will you please do a video on mirrors? Like how mirrors can make your reflection appear skinnier (something exploited by department stores throughout the world)? And how two-way mirrors work and how to tell if you are being observed through one?
this channel deserves a lot more viewer
Great video - until now, angular momentum was more something I could kind of calculate with, rather than something I really understood well.
you couldn't have explained this concept any better. Thanks bro!
thx ! just what i needed for my basic physics test in 2 weeks!
I think the first example with the wheel is a bit misleading. Calculating angular momentum from the center of the wheel should account for its moment of inertia.
Angular Momentum = (moment of inertia) x (angular velocity)
When the moment of inertia is (Mass) x (Radius)^2 the formula would indeed simply be (Mass) x (Radius) x (Velocity). Fortunately, in the case of a bike wheel (which is also why I think it was chosen to be an example in the first place), it can be modeled as a hoop/ring, which does have moment of inertia of MR^2.
But if it was a disk instead (so maybe one of those plastic bike wheels someone made), which has a moment of inertia of 1/2 MR^2, the formula for its angular momentum would become 1/2 x (Mass) x (Radius) x (Velocity).
All in all, I guess it's no problem? lol I just wish he would have mentioned briefly about moment of inertia while using that example.
+Hyeon Woo Shim been a while since i last looked at this but i think you get the unconditional version by integrating mvr even when not first deriving moment of inertia
1:50 Angular momentum does not stay "roughly constant", it stays fucking constant.
Kepplers second law dammit!
very good explanation for importance of angular momentum
THANK YOU. Physics explained by you guys makes class SO much easier. 👍