You make science extremely interesting and you know how to keep people interested, you see the kind of teacher any student would be lucky to have. If I had you as my science teacher I wouldn't fall asleep
There are teachers and there are born teachers . You sir, are a member of the second group . Those kids will remember Newtons 3 rd law of motion all their lives thanks to you !
Bruce you seem like the kind of teacher that can change the lives of the students you teach. You get excited over science and want to make science and physics a visual subject and not a subject full of regurgitating equations repeatedly (granted there always has to be some of that). A high school teacher like yourself that I had changed my life and is the reason I have become an engineer. Thank you for what you do.
Shout out to you for supplying some nice home "labs" for my children! We are now home schooled due to quarantine closures. I particularly like how you covered a part of the experiment I never did as a kid. The difference between a heavier and lighter cart.
Thank you. Your explanation of cannon recoil as caused by the gas expanding both forward and backwards is one of the few correct explanations on TH-cam. The expansion of gas is also the correct explanation for rocket acceleration. However, neither case is an example of Newton's third law. The law states that if body A exerts a force on body B, body B will exert the same force on body A, but in the opposite direction. The cannon and the ball do not exert forces on each other. It's the gas that generates all the forces.
Awesome demonstration. I did some basic calculations. Looks like the ball went about 45 m when you launched it upwards. Did you have your students calculate that?
Okay, cool. Hello from Florida. I'm a high school student down here and I'm really into physics. Hoping to be a mechanical engineer. Thanks for putting out these great videos!
Hey Bruce! This is great, I'm a mechanical engineering student right now but this took me back to high school when my physics teacher built a potato cannon out of PVC to demonstrate the same things you are here, just wanted to share that I think this is great and keep up the good work! Oh, and if the potato cannon I mentioned caught your attention I still have a PDF of the plans for it if you're interested but I'm sure you know how to make your own if you wanted to.
Using the verticle cannon, you could calculate the height of the ball by tracking the time it takes for the ball to hit the ground... Though this might be more of a porabula maths problem than science... Luckily, Matt Parker is both a maths teacher and loves porabulas and pi. And a colab would be awesome!
The slowmo camera footage around 6:35 kind of reminds me of quantum uncertainty. We can clearly see the ball's motion, but pause and try to pinpoint the ball's precise location. Can't because it's just a blur.
Hey Bruce, I am having trouble recreating the experiment with my set up. I found similar cans, and seem to be looking at a similar amount of fuel but am having issues with the fuel and air mix. If too much lighter fluid is placed in the cannon does not fire. But when too little is used the cannon's fire is underwhelming. I can only get a firing much smaller than yours. Can you speak more on the amount of fuel you use and how long you turn and let it vaporize before firing?
My fuel does not come out in drops unfortunately so its hard to gage how much is too much. If I was to use a pipette how much fuel would you say you are using?
really pisses me off how youtube will magically unsubscribe you from channels that you've repeatedly subscribed to numerous times!! ive subscribed to this channel at least 5 times. screw you youtube!
I remeber seeing something like this on Mr wizard. It was made with 3 cans. Top can had both ends cut out, bottom can had just the top cut out, with the touch hold at the bottom, and the middle can was had half of the lids cut out, but opposite to each other, so that worked to mix up the fuel. he used a cup not a tennis ball. I also remember someone talking about making a polish cannon and I think this device was what he was talking about.
Bruce, you don't have to push the tennis ball all the way to the bottom. The bottom can will need a hole on one edge like using a pop can. I place the lighting hole on the opposite side. I also made a little carburetor to fix the outside problem. I use an air compressor for this.
Made something similar decades ago for duck hunting. (for scaring the ducks off the water and into flight, not for shooting ) Our chambers were different with the firing hole on the bottom instead of the side. Compressed Butane worked the best.
Hi Bruce. I've really enjoyed your videos throughout the year. Your engaging style of fun makes learning so much easier. Have a Happy Christmas and New Year.
If you mounted the cannon at 45 degrees in a rigid mounting, then measured muzzle velocity and horizontal range, you could use it to calculate a basic ballistic trajectory, including allowance for air resistance (by comparing the actual range with the theoretical).
I'm making another video indoors at the moment and then when it gets nice plan to do some testing outdoors. I'd love to try what you you are suggesting but the problem is that the muzzle velocity is not very consistent from one trial to the next.
Yes that's a good point - you'd need to measure it on camera for each shot, and know which range you got each time, and match the two. Perhaps that experiment would work better with a trebuchet.
Hi, I would like to use this in my class but I'm confused about where you put the lighter fluid? Can you explain in detail how the bottom chamber is made? Also, where do you get those wheeled carts?
When you use the wooden cart, since the barrel is loose, you have a secondary instance of the 3rd law as the combustion chamber impacts with the wall of the cart.
Really really nice video Bruce. However in my brain it is still hard to imagine how expanding gas alone could provide thrust to an object in an infinite vacuum. We understand so little about vacuum. I'm sure you have seen the video from Cody's lab where he clearly demonstrated that powder does not burn in a vacuum, and a few other anomalies.
There realy is nothing to understand other then the vacuum is completely unimportant. You throw somthing away from e.g you and you will move in the other direction. Thats all. Try it. Use a skateboard (but make sure that it can run with low friction on the ground), take a bowling ball. Stand on the skateboard, throw the bowling ball in line with the skateboard and you will notice that you (and the skateboard) move into the other direction. You may vary the mass of the object you want to throw away and you will figure out: the more mass (the heavier) the faster you will move in the opposite direction. The faster you throw, the faster you will go in to other direction. Actually the vacuum makes it simpler, since there is no air resistance. Which of course is not important for you and your skateboard but is important once the speeds get higher. But in a nutshell, this is it: thorw away some mass in one direction (you need some forcr to do that) and an opposite force acts on the thrower. This is exactly why swings tip over, if not mounted solid to the ground. The tipover always happens in the opposite direction of the swing. Newtons 3rd law in action. Black poweder does burn in a vaccum. The hard part is to ignite it, since it does not ignite instantanously but needs something to heat it up until it burns. And this is the hard part. But once it burns, it will burn all by itself. Luckily they do not use powder rocket when they are up in orbit. You know why? Because they are rocket engineers. The know all of this and a lot more.
You should try different methods of adding the fuel in that allows for a better mix of fuel and air and also different ratios. Good way to teach kids about stoichiometry.
Was it the friction of the tennis ball moving the barrel forwards from the cart, maybe if you greased the tennis ball there would be less friction so it would sit snug to the base of the cart...
Ação e reação ( 3 Lei de Newton) Very nice Bruce!!!! :D Bruce, if an electron gun were to be used instead of this combustion cannon, would it have the same effect of having a reaction that drives a propulsion?
this is not really my area buttI would think that since the electrons have so little mass, that even at the high velocity from an electron gun there would not be enough force generated to move as propulsion
regarding this barrel motion, the center of mass of the system moves exactly as expected, when the system is falling apart. great opportunity to introduce the notion of the center of mass! it is not the cart and not the barrel it is a system of moving parts, that can be ABSTRACTED (when it is isolated in a proper sense) and the law applied to the system as a whole.
Center of mass is a nifty little shortcut to solving conservation of momentum problems. And I feel, it gives you greater insight in to what is really happening. Inelastic collisions are easy in the lab reference frame to solve. Just a weighted average of the velocities, and that's your final velocity, which also ends up being the velocity of the center of mass. Elastic collisions in the lab reference frame are much more complicated to solve, as you end up with a quadratic formula to solve, which would lose half your students You also get two solutions: one is the trivial solution that no collision happens, and the other is the one we want. If you shift your reference frame to the center of mass of the two objects colliding, what you find is that the two masses that elastically collide, simply reverse their velocities in the center of mass reference frame. So you find the velocity of the center of mass, translate given velocities to the center of mass reference frame, reverse both of them, and then translate velocities back to the lab reference frame. No quadratic formula needed at all.
I used to make those as a kid. But I remember there being a way bigger blast and they kicked like a mule. We would get hangtimes of 6 or 8 seconds. We would shake the heck out of them after adding the lighter fluid to make it vaporize more. Lol also learned the hard way to remove the wrappers from cans before taping them together. They blew apart . Then the aluminum tape blew apart but the duct tape held good. Now they're making potato canons from pvc pipe (dangerous) and propelling them using butane and a piezoelectric igniter for bbq grill..
Hi J dog, what you describe is why I've kept mine small especially when using it with students. I have a PVC compressed air cannon, 3 inch diameter barrel, I felt I had more control and safer than the explosive types
@@YeanyScience actually, pvc it a bad choice for handling compressed air. It can handle high pressures . However, should it fail, the outcome can be deadly as PVC will burst into glass like shards. As a formally educated commercial plumber, we can never pump it up to more than 5 PSI if using a gas like air or nitrogen or wherever. If we are performing bhydrostatic test, then it's okay to pump up to 150psi. But we rarely use PVC for anything that requires a hydrostatic pressure test. Sometimes if we're running waste lines under the water table, like by the shoreline, we'll run them in PVC but they only have to pass with a 10' head of water column (4.54 PSI).. Anyway, I wonder if you could rifle the barrel of the cannon? If YOU could make it water tight , before poking the ignition hole, fill it up with water and freeze it. Then , using a coiled piece of wire as a guide, use something like a window screen rolling tool (like a blunt pizza cutter), push in some rifling into the barrel and see what that does to the data... ...maybe one revolution along the length of the barrel, 3 equally spaced places. Using the radius to mark it off with dividers or compass.. OOohe! You know what would work to back up the cans as the rifling is rolled into the cans..? ...a 2" test balloon. We use them to plug up our 2" waste lines to be tested. They're a thick lined rubber tube that is pumped up with a bicycle pump.. Like angioplasty..
I find it interesting the barrel doesn't stay seated. Perhaps the the barrel is too long? (Hot gasses have cooled off by the time the ball reaches the end leaving a partial vacuum in the chamber "sucking" the ball back and pulling the chamber forward?
First, during firing the pressure pulse causes the cart to move, but the passing of inertia causes the cannon to lag. Second, the positive pressure wave forces the ball out of the tube and still ejects gas after that, leaving a negative pressure inside the tube which must be filled/neutralized. So in essence the tube is sucked away from the cart, so you were nearly right. Those positive and negative waves are what are used in making exhaust systems for internal combustion engines in cars and other things. Hope this helped.
Thanks Jay, we didn't notice it until watching the videos, now as I watch more closely, the cannon doesn't become unseated and move forward until after the ball exits the barrel so what you are saying makes sense.
My. choice of fuel is lighter fluid. I have seen or heard of using other fuels. I don't know how they compare to what I use, the list includes alcohols, hair spray, propane, methane, gasoline, hydrogen. There is a list on the internet that compares the fuels and rates them, you'll have to do a search for it as I don't currently have it's URL
This surprised me because I had no idea that lighter fluid was that volatile, it seems so much more docile in say a Zippo lighter. Now I'm wondering how this would work using starting fluid, gasoline or even Coleman fuel. After watching this I doubt that a can like that would hold up to those fuels, maybe PVC pipe with some reinforcement or steel pipe. I remember some neighbor kids doing this in the late 70s (3 brothers) in our elementary school field with a tennis can or two connected somehow but I don't remember what they used for fuel, it's just been too long ago. I do remember the tennis ball going way up in the air. This was around the same time that my dad got me into model rockets, it was a lot of fun.
7:40 It shouldn't matter if all the gases were contained or not; the motion is driven from the ball being launched. The gases leaking out makes the launch less efficient, but shouldn't have an effect on the ratio of velocity for each object. Same for the barrel not remaining seated in the cart. Although some energy is lost to friction in the form of heat between the barrel and cart, it should be minimal compared to the kinect energy of the barrel and not effect the velocity too much..
Hello Suedocode, I have some ideas on how Ican test this, it should be interesting to see what is going on. I hope to give a try it in the near future and will post whatever I find out
"... Although some energy is lost to friction in the form of heat between the barrel and cart..." I want to quickly revisit what I said after further thought. The friction between the barrel and cart should _not_ affect the transfer of momentum; it's identical to an inelastic collision where two balls stick upon impact. In this case, the "stick" part is friction between the barrel and cart over time rather than instantaneously. The energy lost to friction as heat would have been lost anyway even in a rigid set up, although the heat profile might be a bit different. This is can be proven with P and KE equations if you need them. I'll keep an eye out for the next video's results! I love seeing enthusiastic educational physics videos like yours.
@@Suedocode You are correct. Internal forces between the ball and cannon should not affect the ratio of final velocities. This should work like an inelastic collision in reverse. Instead of energy exiting the mechanical domain as a result of the interaction, energy enters the mechanical domain from the work done by the expanding hot gasses. The two bodies start together, depart in opposite directions, and even with friction between the two of them, they should conserve momentum. What WOULD impact conservation of momentum verification in this experiment, are the following factors: 1. The fact that the cannon is on wheels that roll, which adds to the effective inertia of the cannon-wheel system. 2. The friction and rolling resistance between the wheels, axles, and ground 3. Air drag, the obvious answer in nearly every problem that takes place on our planet. 4. Thrust from the gasses leaving the ignition hole, and applying a force in a direction you didn't intend.
Hi, I'm trying to make one for my class and I don't have success. Do the cans need to be smooth on the inside? I used cans with ridges coz I cannot find the cans in stores that you used here.
Yes. Because the energy would be dedicated to making the ball move forward, without absorbing it in the recoil of the cannon. A practical example of where you see this, is when you are driving your car in slippery mud, compared to when you are driving it on a dry road. On a dry road, you grip the road well enough to push backward on the entire planet, and have the Earth reflect the work done by the engine back onto the car to make it move forward. The vast majority of the work done by the engine becomes work done on the car, due to the interacting mass being so large it might as well be infinitely larger than the mass of the car. But when you drive on slippery mud, and just push backward on a couple of kilograms of mud, the same work done by the engine is wasted on pushing mud backwards, and little (if any) of the energy becomes work done on the car. For propulsion, you need a source of momentum, and a source of energy. You have to push backwards on something to push yourself forward. Cars, trains, bikes, and people walking have the advantage of pushing backward on the whole planet at once. While ships and airplanes push backwards on a parcel of fluid that doesn't directly act on the Earth, and for planes in particular, the nozzle thrust moves backward a lot faster than the plane moves forward. Rockets have the ultimate disadvantage, because their propellant has to be both the source of energy and the source of momentum, and generally don't get to interact with any other source of momentum along the way.
thanks D Smith, maybe you're young enough that I could have had you as a student. I've taught some students that are now grandparents, I started teaching in 1977.
:-) certainly young enough. just the wrong country. I never saw a teacher like this in Australia. I expect your style of teaching would not be allowed in our nanny state.
I made one as a kid, Her is how, its much better and easier to make but may cost a little more: Use PVC pipe for your barrel with a screw on cap at one end, Drill a hole in the side at the bottom end for the igniter about 100mm from the bottom (use a spade bit). Then you just put in a quarter filled coke bottle(it fits perfectly) in from the front and push down til 1 inch before the ignitor then finally just spray fly spray into the bottom, quickly screw the cap on and push the ignitor to fire, Use caution as this will be way more powerful than this one in the video and will send someone to hospital if aimed at a person
I'll soon be trying to run some new tests on the cannon and hope to answer that question. Couple ideas, 1. the friction between the ball and the barrel is enough to pull it along, 2. it's some kind of rebound off the back edge of the cart. 3. as the ball leaves the barrel there is a decrease in pressure inside the barrel, atmospheric pressure in pushing it forward. I'm open to other ideas
And if the students are calculus-inclined, they could calculate the initial pressure at ignition, assuming air is representative of the gasses in the chamber, and adiabatic expansion represents the pressure-volume curve. That's how you calculate the work done by the power stroke in an internal combustion engine.
as the mass increases the pull of gravity will increases at the same rate. double the mass of an object means double the gravitational pull, gravity is pulling twice the as hard, three times the mass means three times as much pull ans so on, as long as we can ignore air resistance all the objects still accelerate together
The cannon is not a solid item and the kinetic energy is transferred between the barrel and the cart so securing them together will most definitely change the results.
When I was a youth we tried using model airplane fuel, (methanol and nitro methane) for our tennis ball cannons. That worked good for a short time but after a few good shots the cans would start to come apart at the seams. It was kind of scary.
After seeing your videos where you use so much time on practical examples, and putting your self out there, I was inspired to do my own practical example of newtons 1. and 2. law. I put op 10 bottles of water, and trew a pingpong ball at it. Than I sendt my self at it lying on a skateboard, changing the mass, and therefor changing the force on the bottles. It was a great moment with my students, and it made the connection on top the rest of the subject. Heres a clip of me running down the bottles at my school: th-cam.com/video/tFSHmc-E8IY/w-d-xo.html
Loved it, these are the types of moments kids will remember 20 years from now when you see them all grown up and they have their own kids. You'll run into them somewhere and recount it as something they'll remember all their lives.
Teachers that play with fire...
... are the best teachers ever!
You make science extremely interesting and you know how to keep people interested, you see the kind of teacher any student would be lucky to have. If I had you as my science teacher I wouldn't fall asleep
There are teachers and there are born teachers . You sir, are a member of the second group . Those kids will remember Newtons 3 rd law of motion all their lives thanks to you !
This is awesome! Also it is funny how he says Ok. Bye. And the walks out of the room.
Bruce you seem like the kind of teacher that can change the lives of the students you teach. You get excited over science and want to make science and physics a visual subject and not a subject full of regurgitating equations repeatedly (granted there always has to be some of that). A high school teacher like yourself that I had changed my life and is the reason I have become an engineer. Thank you for what you do.
Shout out to you for supplying some nice home "labs" for my children! We are now home schooled due to quarantine closures. I particularly like how you covered a part of the experiment I never did as a kid. The difference between a heavier and lighter cart.
hope the schooling is going well, I always loved the cannons, what surprised me the most was the change in barrel length
You are the kid of teacher that can change a child's life by getting them interested in physics. Keep up the good work!
Thank you. Your explanation of cannon recoil as caused by the gas expanding both forward and backwards is one of the few correct explanations on TH-cam. The expansion of gas is also the correct explanation for rocket acceleration. However, neither case is an example of Newton's third law. The law states that if body A exerts a force on body B, body B will exert the same force on body A, but in the opposite direction. The cannon and the ball do not exert forces on each other. It's the gas that generates all the forces.
Nicely done! I hope every kid gets a science teacher like you.
Great Job Bruce. We enjoy your videos and your approach to thinking and reasoning.
Cool that you also covered Newton's Second Law and took the time to look at factors that can affect results.
Thanks Slater, Newton's law are a matched set, hard to teach one without the others. Hope you're doing well and have a nice thanksgiving.
Great work Bruce. I think I might have to build one of those. Thank you for sharing.
Hey Bruce! Awesome demonstration and amazing DIY skills, as usual... ^^
Thumb up and cheers!
Awesome demonstration. I did some basic calculations. Looks like the ball went about 45 m when you launched it upwards. Did you have your students calculate that?
Thank you, we didn't, I have middle school students. In the future it might be fun to take a look at some angled trajectories.
Okay, cool. Hello from Florida. I'm a high school student down here and I'm really into physics. Hoping to be a mechanical engineer. Thanks for putting out these great videos!
You are an awesome teacher man. I know you really enjoy your work and so do the students
Hey Bruce! This is great, I'm a mechanical engineering student right now but this took me back to high school when my physics teacher built a potato cannon out of PVC to demonstrate the same things you are here, just wanted to share that I think this is great and keep up the good work!
Oh, and if the potato cannon I mentioned caught your attention I still have a PDF of the plans for it if you're interested but I'm sure you know how to make your own if you wanted to.
Bruce, you must have a blast with such great young minds :)
physics and cannons, coolest video ever
Excelente... Muy buen trabajo profesor. Soy guatemalteco su creatividad es admirable.
Using the verticle cannon, you could calculate the height of the ball by tracking the time it takes for the ball to hit the ground...
Though this might be more of a porabula maths problem than science... Luckily, Matt Parker is both a maths teacher and loves porabulas and pi. And a colab would be awesome!
The slowmo camera footage around 6:35 kind of reminds me of quantum uncertainty. We can clearly see the ball's motion, but pause and try to pinpoint the ball's precise location. Can't because it's just a blur.
Hey Bruce, I am having trouble recreating the experiment with my set up. I found similar cans, and seem to be looking at a similar amount of fuel but am having issues with the fuel and air mix. If too much lighter fluid is placed in the cannon does not fire. But when too little is used the cannon's fire is underwhelming. I can only get a firing much smaller than yours. Can you speak more on the amount of fuel you use and how long you turn and let it vaporize before firing?
My fuel does not come out in drops unfortunately so its hard to gage how much is too much. If I was to use a pipette how much fuel would you say you are using?
Your channel is growing fast!
really pisses me off how youtube will magically unsubscribe you from channels that you've repeatedly subscribed to numerous times!! ive subscribed to this channel at least 5 times. screw you youtube!
I remeber seeing something like this on Mr wizard. It was made with 3 cans. Top can had both ends cut out, bottom can had just the top cut out, with the touch hold at the bottom, and the middle can was had half of the lids cut out, but opposite to each other, so that worked to mix up the fuel. he used a cup not a tennis ball. I also remember someone talking about making a polish cannon and I think this device was what he was talking about.
Hi! Instead of lighter fluid, can you use ethanol or regular alcohol?
Bruce, you don't have to push the tennis ball all the way to the bottom. The bottom can will need a hole on one edge like using a pop can. I place the lighting hole on the opposite side. I also made a little carburetor to fix the outside problem. I use an air compressor for this.
Hlo sir... Great fan / student... Learn a lot of things from u r video
I really like physics and u made me do that... Please reply 👌👌
Very nice👍. Thank you Bruce.
Made something similar decades ago for duck hunting. (for scaring the ducks off the water and into flight, not for shooting ) Our chambers were different with the firing hole on the bottom instead of the side. Compressed Butane worked the best.
Love it. Great video Bruce.
Great video Bruce! What speed would it travel if you hang the cannon from a string in order to reduce the friction it has with the floor?
Hi Bruce. I've really enjoyed your videos throughout the year. Your engaging style of fun makes learning so much easier. Have a Happy Christmas and New Year.
Thank you Spoif, Hope your's is happy as well
They are lucky kids to have a teacher like him.
thanks for this video. I am building a wood cart. where did you find the plastic cart??
Steve Spangler science
Your videos are fantastic!!
If you mounted the cannon at 45 degrees in a rigid mounting, then measured muzzle velocity and horizontal range, you could use it to calculate a basic ballistic trajectory, including allowance for air resistance (by comparing the actual range with the theoretical).
I'm making another video indoors at the moment and then when it gets nice plan to do some testing outdoors. I'd love to try what you you are suggesting but the problem is that the muzzle velocity is not very consistent from one trial to the next.
Yes that's a good point - you'd need to measure it on camera for each shot, and know which range you got each time, and match the two. Perhaps that experiment would work better with a trebuchet.
Hello Mr. Bruce Yeany. I really like their videos, but it would be great if I put subtitles in Spanish, to understand better. Greetings.
I'm not sure how to do that
Hi, I would like to use this in my class but I'm confused about where you put the lighter fluid? Can you explain in detail how the bottom chamber is made? Also, where do you get those wheeled carts?
A CAN-NON. Literally. It's made of cans.
Brian Wyters nice
nice
When you use the wooden cart, since the barrel is loose, you have a secondary instance of the 3rd law as the combustion chamber impacts with the wall of the cart.
Really really nice video Bruce. However in my brain it is still hard to imagine how expanding gas alone could provide thrust to an object in an infinite vacuum. We understand so little about vacuum. I'm sure you have seen the video from Cody's lab where he clearly demonstrated that powder does not burn in a vacuum, and a few other anomalies.
There realy is nothing to understand other then the vacuum is completely unimportant. You throw somthing away from e.g you and you will move in the other direction. Thats all. Try it. Use a skateboard (but make sure that it can run with low friction on the ground), take a bowling ball. Stand on the skateboard, throw the bowling ball in line with the skateboard and you will notice that you (and the skateboard) move into the other direction. You may vary the mass of the object you want to throw away and you will figure out: the more mass (the heavier) the faster you will move in the opposite direction. The faster you throw, the faster you will go in to other direction.
Actually the vacuum makes it simpler, since there is no air resistance. Which of course is not important for you and your skateboard but is important once the speeds get higher. But in a nutshell, this is it: thorw away some mass in one direction (you need some forcr to do that) and an opposite force acts on the thrower. This is exactly why swings tip over, if not mounted solid to the ground. The tipover always happens in the opposite direction of the swing. Newtons 3rd law in action.
Black poweder does burn in a vaccum. The hard part is to ignite it, since it does not ignite instantanously but needs something to heat it up until it burns. And this is the hard part. But once it burns, it will burn all by itself. Luckily they do not use powder rocket when they are up in orbit. You know why? Because they are rocket engineers. The know all of this and a lot more.
Very nice
Put the canon over a weighing scale before vertical fire.
You should try different methods of adding the fuel in that allows for a better mix of fuel and air and also different ratios. Good way to teach kids about stoichiometry.
Was it the friction of the tennis ball moving the barrel forwards from the cart, maybe if you greased the tennis ball there would be less friction so it would sit snug to the base of the cart...
I'm right in the middle of making another video on this, I'll have some interesting results
Ação e reação ( 3 Lei de Newton)
Very nice Bruce!!!! :D
Bruce, if an electron gun were to be used instead of this combustion cannon, would it have the same effect of having a reaction that drives a propulsion?
this is not really my area buttI would think that since the electrons have so little mass, that even at the high velocity from an electron gun there would not be enough force generated to move as propulsion
you can find this plastic frame is from? I called it a soda + mentos powered car kit.
regarding this barrel motion, the center of mass of the system moves exactly as expected, when the system is falling apart.
great opportunity to introduce the notion of the center of mass!
it is not the cart and not the barrel it is a system of moving parts, that can be ABSTRACTED (when it is isolated in a proper sense) and the law applied to the system as a whole.
Center of mass is a nifty little shortcut to solving conservation of momentum problems. And I feel, it gives you greater insight in to what is really happening.
Inelastic collisions are easy in the lab reference frame to solve. Just a weighted average of the velocities, and that's your final velocity, which also ends up being the velocity of the center of mass. Elastic collisions in the lab reference frame are much more complicated to solve, as you end up with a quadratic formula to solve, which would lose half your students You also get two solutions: one is the trivial solution that no collision happens, and the other is the one we want.
If you shift your reference frame to the center of mass of the two objects colliding, what you find is that the two masses that elastically collide, simply reverse their velocities in the center of mass reference frame. So you find the velocity of the center of mass, translate given velocities to the center of mass reference frame, reverse both of them, and then translate velocities back to the lab reference frame. No quadratic formula needed at all.
Awesome teachers make learning fun! How about comparing canon barrels of different length? Will a longer barrel result in a higher speed?
HI Peter, good idea, I have a few more things I want to try with it also.
I would expect a longer barrel to result in a higher speed, due to more distance that the expanding gasses can apply a force to the ball.
I used to make those as a kid. But I remember there being a way bigger blast and they kicked like a mule. We would get hangtimes of 6 or 8 seconds. We would shake the heck out of them after adding the lighter fluid to make it vaporize more. Lol also learned the hard way to remove the wrappers from cans before taping them together. They blew apart . Then the aluminum tape blew apart but the duct tape held good. Now they're making potato canons from pvc pipe (dangerous) and propelling them using butane and a piezoelectric igniter for bbq grill..
Hi J dog, what you describe is why I've kept mine small especially when using it with students. I have a PVC compressed air cannon, 3 inch diameter barrel, I felt I had more control and safer than the explosive types
@@YeanyScience actually, pvc it a bad choice for handling compressed air. It can handle high pressures . However, should it fail, the outcome can be deadly as PVC will burst into glass like shards. As a formally educated commercial plumber, we can never pump it up to more than 5 PSI if using a gas like air or nitrogen or wherever. If we are performing bhydrostatic test, then it's okay to pump up to 150psi. But we rarely use PVC for anything that requires a hydrostatic pressure test. Sometimes if we're running waste lines under the water table, like by the shoreline, we'll run them in PVC but they only have to pass with a 10' head of water column (4.54 PSI)..
Anyway, I wonder if you could rifle the barrel of the cannon? If YOU could make it water tight , before poking the ignition hole, fill it up with water and freeze it. Then , using a coiled piece of wire as a guide, use something like a window screen rolling tool (like a blunt pizza cutter), push in some rifling into the barrel and see what that does to the data... ...maybe one revolution along the length of the barrel, 3 equally spaced places. Using the radius to mark it off with dividers or compass.. OOohe! You know what would work to back up the cans as the rifling is rolled into the cans..? ...a 2" test balloon. We use them to plug up our 2" waste lines to be tested. They're a thick lined rubber tube that is pumped up with a bicycle pump.. Like angioplasty..
I find it interesting the barrel doesn't stay seated. Perhaps the the barrel is too long? (Hot gasses have cooled off by the time the ball reaches the end leaving a partial vacuum in the chamber "sucking" the ball back and pulling the chamber forward?
First, during firing the pressure pulse causes the cart to move, but the passing of inertia causes the cannon to lag.
Second, the positive pressure wave forces the ball out of the tube and still ejects gas after that, leaving a negative pressure inside the tube which must be filled/neutralized. So in essence the tube is sucked away from the cart, so you were nearly right. Those positive and negative waves are what are used in making exhaust systems for internal combustion engines in cars and other things. Hope this helped.
Thanks Jay, we didn't notice it until watching the videos, now as I watch more closely, the cannon doesn't become unseated and move forward until after the ball exits the barrel so what you are saying makes sense.
Almost as if air has mass, eh? Compression and rarefaction.
It's why I read the comments, it's a learning experience for me.
Also the amount of lighter fluid could affect speeds
good point, thanks
Bruce Yeany you have great science videos as well!
Sir what did you use for fuel and please also share other alternatives
My. choice of fuel is lighter fluid. I have seen or heard of using other fuels. I don't know how they compare to what I use, the list includes alcohols, hair spray, propane, methane, gasoline, hydrogen. There is a list on the internet that compares the fuels and rates them, you'll have to do a search for it as I don't currently have it's URL
This surprised me because I had no idea that lighter fluid was that volatile, it seems so much more docile in say a Zippo lighter. Now I'm wondering how this would work using starting fluid, gasoline or even Coleman fuel. After watching this I doubt that a can like that would hold up to those fuels, maybe PVC pipe with some reinforcement or steel pipe. I remember some neighbor kids doing this in the late 70s (3 brothers) in our elementary school field with a tennis can or two connected somehow but I don't remember what they used for fuel, it's just been too long ago. I do remember the tennis ball going way up in the air. This was around the same time that my dad got me into model rockets, it was a lot of fun.
We used to use these for "fireworks" during New Year's. Long bamboo instead of cans and no tennis balls= loud bang. Same principle.
Wish you were my teacher growing up !
doin gods own work Yeany
Could you have dipped the base of a string in lighter fluid, shoved that into the hole, then lit that to prevent leakage outside?
Great content....wish I was a 7th grader in your class.
7:40 It shouldn't matter if all the gases were contained or not; the motion is driven from the ball being launched. The gases leaking out makes the launch less efficient, but shouldn't have an effect on the ratio of velocity for each object.
Same for the barrel not remaining seated in the cart. Although some energy is lost to friction in the form of heat between the barrel and cart, it should be minimal compared to the kinect energy of the barrel and not effect the velocity too much..
Hello Suedocode, I have some ideas on how Ican test this, it should be interesting to see what is going on. I hope to give a try it in the near future and will post whatever I find out
"... Although some energy is lost to friction in the form of heat between the barrel and cart..."
I want to quickly revisit what I said after further thought. The friction between the barrel and cart should _not_ affect the transfer of momentum; it's identical to an inelastic collision where two balls stick upon impact. In this case, the "stick" part is friction between the barrel and cart over time rather than instantaneously. The energy lost to friction as heat would have been lost anyway even in a rigid set up, although the heat profile might be a bit different. This is can be proven with P and KE equations if you need them.
I'll keep an eye out for the next video's results! I love seeing enthusiastic educational physics videos like yours.
@@Suedocode You are correct. Internal forces between the ball and cannon should not affect the ratio of final velocities. This should work like an inelastic collision in reverse. Instead of energy exiting the mechanical domain as a result of the interaction, energy enters the mechanical domain from the work done by the expanding hot gasses. The two bodies start together, depart in opposite directions, and even with friction between the two of them, they should conserve momentum.
What WOULD impact conservation of momentum verification in this experiment, are the following factors:
1. The fact that the cannon is on wheels that roll, which adds to the effective inertia of the cannon-wheel system.
2. The friction and rolling resistance between the wheels, axles, and ground
3. Air drag, the obvious answer in nearly every problem that takes place on our planet.
4. Thrust from the gasses leaving the ignition hole, and applying a force in a direction you didn't intend.
Good teacher
Hi, I'm trying to make one for my class and I don't have success. Do the cans need to be smooth on the inside? I used cans with ridges coz I cannot find the cans in stores that you used here.
WoOw really a good teacher
I can improve my TH-cam videos by this channel.
If the cannon is stopped from moving, would the ball travel further?
Yes. Because the energy would be dedicated to making the ball move forward, without absorbing it in the recoil of the cannon.
A practical example of where you see this, is when you are driving your car in slippery mud, compared to when you are driving it on a dry road. On a dry road, you grip the road well enough to push backward on the entire planet, and have the Earth reflect the work done by the engine back onto the car to make it move forward. The vast majority of the work done by the engine becomes work done on the car, due to the interacting mass being so large it might as well be infinitely larger than the mass of the car. But when you drive on slippery mud, and just push backward on a couple of kilograms of mud, the same work done by the engine is wasted on pushing mud backwards, and little (if any) of the energy becomes work done on the car.
For propulsion, you need a source of momentum, and a source of energy. You have to push backwards on something to push yourself forward. Cars, trains, bikes, and people walking have the advantage of pushing backward on the whole planet at once. While ships and airplanes push backwards on a parcel of fluid that doesn't directly act on the Earth, and for planes in particular, the nozzle thrust moves backward a lot faster than the plane moves forward. Rockets have the ultimate disadvantage, because their propellant has to be both the source of energy and the source of momentum, and generally don't get to interact with any other source of momentum along the way.
In my youth we would do this with the old tennis ball cans. We didn't know about wetting the ball, alot of burnt gas as a result.
Hello Bruce, what is the name of the fuel you have used? Please suggest alternate powerful fuels for the same.
it is lighter fuel, I've also used alcohols
love your stuff dude. and i'm so old i have kids old enough to be in your class. hahaha. keep up the great work.
thanks D Smith, maybe you're young enough that I could have had you as a student. I've taught some students that are now grandparents, I started teaching in 1977.
:-) certainly young enough. just the wrong country. I never saw a teacher like this in Australia. I expect your style of teaching would not be allowed in our nanny state.
Bruce you are my messiah
Girls: Ok, a simple cannon, we can do this
Boys: READY! AIM! FIRE! *THUNK* RELOAD!
It would be great if you could put some lead shot in the tennis balls to make them the same weight as the lighter of the two carts.
good idea, I'll add that to a few other changes I'd like to try. Hope to do a follow-up on this in the future
Just what I was about to say. Since he alters the mass of the canon, can also alter the mass of the ball and see how that changes things.
Lead is always welcome!(obviously a joke, I think steel would poison less kids)
What he put inside what is this yellow water ?
I made one as a kid, Her is how, its much better and easier to make but may cost a little more:
Use PVC pipe for your barrel with a screw on cap at one end, Drill a hole in the side at the bottom end for the igniter about 100mm from the bottom (use a spade bit). Then you just put in a quarter filled coke bottle(it fits perfectly) in from the front and push down til 1 inch before the ignitor then finally just spray fly spray into the bottom, quickly screw the cap on and push the ignitor to fire,
Use caution as this will be way more powerful than this one in the video and will send someone to hospital if aimed at a person
We use to call these polish cannons
What is the solution you put inside and then burnt it to give the ball so much speed?
there are several fuels you could use, I like to use lighter fluid
Can you give the name of the one you used please? Quantity etc and from where I can get them? And alternate ones that areavailable..
Binaca breath spray works better than lighter fluid. Very consistent and more powerful than lighter fluid.
Amazing
I welded one up that runs on Oxy/Pro. It’ll launch a ball over 1500 ft.
that is incredible, also way too much for me to try in a school setting.
I'm going to drop out of college & go back to grade school just so I can be in Mr. Yeany's class.
Why does the barrel move forward relative to the cart?
I'll soon be trying to run some new tests on the cannon and hope to answer that question. Couple ideas, 1. the friction between the ball and the barrel is enough to pull it along, 2. it's some kind of rebound off the back edge of the cart. 3. as the ball leaves the barrel there is a decrease in pressure inside the barrel, atmospheric pressure in pushing it forward. I'm open to other ideas
Can u make a video on home made telescope to observe night sky....
Awesome !
I used to make these when I was kid.I used duck the canan was over 6 feet the ball can shoit up to 500 plus feet
You could have your students calculate the average gas pressure required to result in the measured muzzle velocity.
And if the students are calculus-inclined, they could calculate the initial pressure at ignition, assuming air is representative of the gasses in the chamber, and adiabatic expansion represents the pressure-volume curve. That's how you calculate the work done by the power stroke in an internal combustion engine.
I want to go to this school
how much asparagus did you have to eat to make the cannon?
too much, some of it was frozen and will be eaten in the future (maybe)
What kind of liquid is he using?
What grade do you teach?
If different masses under the same force have different accelerations why do different masses under gravity have the same acceleration?
as the mass increases the pull of gravity will increases at the same rate. double the mass of an object means double the gravitational pull, gravity is pulling twice the as hard, three times the mass means three times as much pull ans so on, as long as we can ignore air resistance all the objects still accelerate together
Bruce Yeany Thank' s I get it now.
Damn u can use this as a cricket bowling machine
The cannon is not a solid item and the kinetic energy is transferred between the barrel and the cart so securing them together will most definitely change the results.
thanks, reggiep75, I didn't realize it until we watched the videos of it
When I was a youth we tried using model airplane fuel, (methanol and nitro methane) for our tennis ball cannons. That worked good for a short time but after a few good shots the cans would start to come apart at the seams. It was kind of scary.
GREAT
I wish he can be my science teacher...
This is William good job
I wish we could make explosions/shoot stuff in science class. If I made an explosion during school I would be expelled.
Sorry i liked before viewing ;]
رائع جدا✋🌿👍
Cool
After seeing your videos where you use so much time on practical examples, and putting your self out there, I was inspired to do my own practical example of newtons 1. and 2. law. I put op 10 bottles of water, and trew a pingpong ball at it. Than I sendt my self at it lying on a skateboard, changing the mass, and therefor changing the force on the bottles. It was a great moment with my students, and it made the connection on top the rest of the subject. Heres a clip of me running down the bottles at my school: th-cam.com/video/tFSHmc-E8IY/w-d-xo.html
Loved it, these are the types of moments kids will remember 20 years from now when you see them all grown up and they have their own kids. You'll run into them somewhere and recount it as something they'll remember all their lives.
Oh, come on man! Have you never heard of a countdown? :)