MIT Physics: Spinning Bike Wheel and Conservation of Angular Momentum
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- čas přidán 15. 08. 2017
- When Ryan spins a bike wheel, nothing crazy happens. But something weird happens when he flips it over - watch and learn as he shows and explains why.
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made with love at MIT
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Written and produced by: Elizabeth Choe
Directed by: George Zaidan
Editing and animations by: Per Hoel
Camera: Adam Morrell
Hosted by: Ryan Robinson
Special thanks for content reviewing: MIT Technical Services Group, Andy Neely
Never in my wildest dreams have I ever imagined young Will Smith teaching me Physics. Great video nonetheless.
Will Smith😂😂😂😂
Gemini man
Fresh Prince of MIT
Homie do resemble Will smith a little with that fade 😅
@@hondobeans Go see an ophthalmologist because you're blind
this was the coolest angular momentum video I watched today
Prolly the only angular momentum video xD
@@hamzanazim5943 lmao true
To date*
@@hamzanazim5943 there are millions
Me as well
This explanation exploded my mind and made me realize angular momentum is a vector resulting from a cross product. Well done, didn't know that.
So you know cross products but didn't know angular momentum was one as well?
@@kaan8964, yes. I took a linear algebra course, but on my undergrad studies we never saw any further application for cross product other than Lorentz Force.
Didn't u know the formula m(r×v)? From there you should have guessed it is a vector product.
@@251rmartin look at me I understand physics
Holy shit I feel like a retard when I read your guy’s messages.
I always played with bike wheels as a kid. Didn't understand why it would have a weird force feeling when moving a spinning wheel. Angular momentum. Thank you!
me too, the weird feeling are cool hahaha
My high school physics teacher showed us this exact demonstration to us. He also used the same rotating platform, sat on it with his legs crossed. He then held a textbook in each hand. When he would bring textbooks close to him, he would spin faster. When he would hold them out, he would spin slower. Because the radius changes, causing the moment of inertia to change
Moment of inertia goes down (because the radius decreases), so angular velocity must go up. There is a great class by Prof. Walter Lewin on it!
Dude this guy tutored me and caught me up to 3 months worth of Algebra in like 2 weeks the guy is a genius but also incredibly down to Earth.
I see what you did there
@@darkeclipse506 lmao was hoping someone would say they got it ✌
@@yronvasquez1851 was the joke “down to earth” or am I slow?😂
@@loes3000 imma level with you...I don't know I think so lmao I was hoping the other guy who said he got it would explain it I just happened to say that
@@yronvasquez1851 Kinda creepy to think you can make a joke without yourself getting it
i love the simplicity of the demonstration.
Now I know how to slow the Earth's rotation and make my days longer! Don't even need the rotating base, only need a bigger wheel... Thanks!
Lmao
i understand but i dont understand why it moves in one direction. i understand what he's saying but dont get it. it's just a wheel spinning. i dont get how the starting position of the wheel would make any difference in rotating. because flipped or not, it's just a spinning wheel.
Bravo! I learned something new. Your demonstration taught how am going to move forward with my design.
I would love to know how you built the turntable. Very well done.
It's made with love
@@seasagar139 at MIT
@@seasagar139 nice one
I can answer that, it's pretty simple really. In West Philadelphia born and raised, on the playground was where he spent most of his days.
I have done this experiment with wheel but I never thought to stand on a free base wheel
Now I understand better
Have u tried with bike wheel that has a longer shaft on one side
@@elimyemily1087 i have, i hung it from a rope
Nd with the other end of longer shaft nd it was moving with an angle with vertical the more the speed the greater is the angle
Lol. Imagine if you actually spun without the free base wheel. You would freak out the whole physics community.
@@HelloWorld-ev9sg i didn't get it, please clarify
@@critisizerr245 It is impossible to spin without the free base wheel. If he spun without the free base wheel, physicists will freak out not knowing what the hell happened, and will most likely spend most of their time seeking answers and reasons how the hell did it happen.
I never knew that will smith belonged to MIT.
Didn’t take a long time to find a will smith joke lol
he do looks like will smith
Fresh Prince Reboot confirmed
not really that funny
*If they had just casted him in Gemini Man instead... the movie would have been more believable.*
Today I'm a Physician but I still remember being taught this lesson in High school Physics. My Physics teacher at that time volunteered me to teach the entire class this lesson because I was the smallest guy in the class and would be able to keep my feet off the ground as I sat on his swivel chair and got spun around by the spinning wheel.
Isn't that physicist and not physician ?
@@sachinfulsunge9977 No one is a physician in high school, but some take physics.
I hated school was aways getting in trouble but luckily in high school Mr Colicott was my physics teacher he was so enthusiastic and passionate about science especially physics, he always tried to make our lessons fun and interesting I'm grateful to him because he introduced a love of learning to me that has carried me through life. Videos like this remind me of those lessons so cool to watch them with my son and then talk about it. He's still young and was already withdrawing from school work but stuff like this even relatively simple demonstrations like these make his eye light up like he's seen a magic trick. Can't wait to hear what questions he comes up with for me after we watch it.
Excellent clear concise explanation and demonstration. Awesome stuff.
The thumb rule is just used to find out the direction of angular momentum
We choose sign acc to our convienience
Sometime outwards is positive ,sometimes it can be negative
I doubt this was meant for test purposes , more to help us understand the concept before we can understand the maths behind it
Question 1: What would happen if the wheel is held further away from the body?
Question 2: If the angular momentum was very high, theoretically would the person be forced to spin and/or have a tendency to move towards an angle?
Question 3: If the weight of the wheel was higher, would the angular momentum be higher?
Thanks in advance folks!
In regards to number 3, yes, angular momentum is equal to I*ω. Greater mass means greater moment of inertia, assuming velocity remains constant, its angular momentum will be higher.
@@batzorigvaanchig6358 In regards to question 1, if the wheel is held further away, the moment of inertia of the system about the base plate"s axis changes (its the only possible axis of rotation), since moment of inertia is directly proportional to the square of the distance from an axis. Hence the guy holding the wheel would rotate with a lower angular frequency after flipping it.
That’s mind blowing it is like magic even though I just studied this subject and took an exam on it
Bunu Türkçye çeviren adam gibi adam kimse çok teşekkür ederimm ona
Benim kardeşim eyvallah yayınlanması çok uzun zaman alıyor 1 yıl önce çevirmiştim acaba yayınlanmış mı diye bakmaya geldim ve yorumunu gördüm yardımcı olduysa ne mutlu bana
@@DrAybars Çok teşekkür ederiz hocam harbiden çok faydalı adamsın
@@DrAybars aynen reis sağol
0:50 It's not angular momentum,
It's just the moment of inertia.
And the claim at the start of the video that it's Newton's third law that makes him spin is also wrong. When he flips the wheel over, the reaction force is a torque that would rotate him about a horizontal axis through his chest and turn him upside down, not a torque about the vertical axis through his spine that rotates him on the turntable.
This was Because of angular momentum.
Came here for this comment, thank you!
I am lost, why is he not spining when the system angular mometum is -L ? does it mean that if he throw away the spinning wheel then the turn table will actually spin anti-clock wise because 0 - L = -L , meaning there is a default angular mometum L if he standing on the turntable without the wheel?
no
When the wheel is spinning in it's own at -L, there is no need for him to spin as the only force that has been applied is to spin the wheel.
When he rotates the wheel and makes its angular momentum +L, there needs to be a correction equal to -2L in order to conserve the wheel's overall momentum, thus it spins him.
Norman xu, i agree, why doesnt he spin the oppisite way, when he flips the wheel over? Its really an unreasonable thing to watch. I guess ima make my own table to turn myself on....i mean, to rotate my self while holding a bike weel.
Anyways, i understand whats happening, but the lack of rotating the other way pulls me to want to make it myself. Good vid. Good question.
Whatever you're standing on has a direction it wants to move in more than the other. You should spin either direction based upon how you hold the wheel, but you only spin one way meaning the thing you're standing on has friction one way but not the other. That is kind of a big part of this demonstration that you leave out.
Kind of a silly way of saying it. "Friction one way but not the other"? He simply put one foot on the ground as he got on the thing he's standing on while holding the wheel. That way he wouldn't initially spin.
@@samusaran13372 well that's not correct, because he turns the wheel back and forth and he remains still with the wheel pointed one of the ways
@@rickdabagian9100 yes, because he started stationary and was handed the wheel.
@@samusaran13372 hell yeah Kanye!
Great demonstration
Thank you sir ! I did not know it has a postive or negative factor in it
This is my kind of physics class
Thanks for explaining it so clearly, Will Smith!
Blasian Will Smith isn’t real 😂
This idea really helped me get through Statics and Dynamic!
That was dope! More please.
Umm....how does the turntable rotate only in one direction and why does it not rotate when turning the wheel one way?
I think it's because he was standing still on the turn table with no angular velocity initially. (At the very beginning of the video he started to spin but the guy held him in place). So then the angular momentum is conserved with only the wheel acting in the closed system (the guy and the wheel).
it might be at start he did a rotation by him-self or receive rotation by another man before he stand up at the rotate-chair.
I took an "L" trying to learn this. . .
same
Agree - if the force is vertical in either wheel position what’s generating the horizontal rotation force (other than the initial force required to torque the wheel from one position to the other)?
More vids with this guy pls
Nice and concise explanation! Very well done
1:05. The moment of inertia depends on its shape and its mass. An object's moment of inertia depends on its geometry AND its density (whether or not the material of the object is uniform, etc.).
Thank you Will Smith for informative video!
Excellent video
Very interesting demonstration of conservation of angular momentum!
Dude.. I just wanna know what bearings he's using hahaha
The set-up of this is fundamentally wrong. When he's standing on the turntable and rotates the wheel, it is correct that there is a Newton's-third-law force in the opposite direction. However, that is not the force that is making him spin: it's not the opposite direction. The opposite direction to him turning the wheel anticlockwise (as seen from our point of view) is a force that tries to turn him clockwise about a horizontal axis through his chest, not about a vertical axis down his spine. The reaction to him flipping the wheel over would turn him upside down, not rotate him on the turntable. The reason it doesn't turn him upside down is that the frictional force through his feet opposes this.
Thank you. My intuition was telling me that there was a torque reaction missing.
CZcams recommend legend after 4 years
hey that demo was done in my uni too... That's why I kinda miss the physics lecture from few semesters back...
Thank you random internet video. I am now even smarter.
Angular momentum is not just conserved here because of your thumb rule
It conserved because all the exteral forces acting on body like gravity is parallel to the axis of rotation
Hello jee aspirant
Pretty sure this would work without gravity, like a floating guy would turn in oppiste direction when the wheel is flipped.
@@generalginger7804
I agree with you
But the points that he was telling about direction were somewhat wrong
@@generalginger7804 would this happen in space then ?
@@camalex7782 Yep. According to my understanding.
I loved your sentences...simple and practical. Great video
Thank you mate very cool
Unfortunately this video is again a hot-mess. At the final sum up you've reversed the directions that you had used in the explanations. In the demos you started with +L as the starting point then the flip to -L is what impels your body into the balancing rotation of +2L. YET, In the final summary, your body was spinning clockwise which meant -2L as a reaction to +L.
Haha Oh dear, when you fail at the correction video.
Bruh what’s will smith doing here
Loved it!
Very well explained😍
People invented the wheel thousand of years ago, and we still have to explain nowadays how it works. 😅
God I want to study at MIT please help me!!
I hope you got there. I'm failing 3 classes at community college right now. One of which is conceptual physics!
This is amazing
Beautiful
Before we catch aliens we must first learn basic physics here that applies to everything and will smith is teaching us
Good job young man!
Awesome!
Love it.. so fascinating .❤️
This helped! Thanks :)
Nice explanation
Has anyone done this but the bottom is rotating (hooked up to a motor I imagine with a "free turning table on top") causing the person to rotate e.g: in a clockwise direction, and then the wheel either makes you rotate twice as fast in one orientation as the forces add or stop in the opposite orientation as the forces cancel out? I feel this would help demonstrate this point even better. Sorry if I'm not very clear with this.
if anyone needs a very good and In a hurry of the explanation of angular momentum and how it works. check this dude out.
I was totally wanting him to do cartwheels when he flipped the wheel vertical
Uncle Phill will be proud of you, Great Video
Hey I've got a question. Assuming the system was in equilibrium at -L means that the an outside force created the equilibrium while you were already on the turntable, (you were on the turntable and then the wheel was spun up). and that's why you were only ever able to spin in one direction.
loved it
1:30 no external torques and not external forces, or net external torque=zero
When you dive, there is an external force but the angular momentum is conserved.
This video really helped. Thank you
Totally a new knowledge for common people
One of my mentor used the wheel chair to explain us angular momentum conservation
This way you balance the y-component of the angular momentum. But if initially, you would hold the wheel vertically, so that it spins around a horizontal axis then the angular momentum is directed to the side. If you then turn the axis to be vertical, you start spinning in order to balance the vertical component of the angular momentum but what does balance the lost horizontal component of the angular momentum?
This looks like its straight out of a movie
Ayoo this trailers hype! Excited to see this movie WiLL.
Daaaaaammmnnn so interesting. Thanks
That was cool!!
If you had started with the bike rim spinning in the opposite direction, would it spin you around the opposite direction when you flipped the wheel?
Bro u r just awesome
Amazing
thank sir
Well explain my dude
I get it perfectly!! THX!
Watching the rest of the video with my hand like this 👍
very cool
Hope they're learning more than that at MIT.
So If I add a mass to that system, but wheel is not moving, could I say angular momentum is not conserved?
Merci Theobabac de tes explications !
PTDRRR, j’me suis dis la même et je suis venu voir si il y avais un commentaire sur sa, je tombe directement sur le tien😭
@@cinco.170 Je croyais être fou ! Tu me rassure haha
Damn MIT now inventing new physics
Not necessary for the external forces to be zero. Although It must not produce torque. For instance gravity is acting here but it produces no torque as it is parallel to the axis of rotation.
what if you keep flipping it the same direction (which will require you to switch hands after each flip) will you keep spinning faster and faster? i’m sure the wheel slows down but you can just spin it more and keep flipping, is it a speed unlock?
This was cool
Totally wholesome
Levee; is one of the things that changes can steal from the opposite that's against; among many many more.
what happens if you take the spinning wheel while pinning does it increase the speed that you spin.. and what if you are spinning opposite direction would it stop your momentum?.. hmmm
Torque. Same reason helicopters use a main rotor for lift, and a tail rotor for stable flight. The tail rotor is spinning counter to the main rotor. Without the tail rotor, the helicopter's entire fuselage would spin like a top, counter to the main rotor.
Airplane propellers are a little different but do the same thing, they are called "tractor propellers". Planes have wings, a rear stablizer and use an airfoil. Their wings produce the lift.
Copter's don't, they rely solely on the pitch of the main rotors for lift.
Plane props spin but the plane remains stable and does not spin.
What happens if he keeps the orientation of the wheel but switches which hand is holding it? Or holds it in front of himself with both hands?
Why didn’t the platform rotate the same speed, opposite direction before it was flipped?
Wait why do you stop when u spin it the other way? Why don't u go to the opposite direction?
This is how "reaction flywheels" on space craft work.speeding up or slowing down any wheel on a given axis will alter the vehicles attitude.
My head just 🤯
so the initial phase is -L, And on the spinning table he stand, every friction is neglected, and we change the wheel's rotation so the angular momentum is preserved?
Man this guys smart asf hes def going to a schoo like MIT
Why don't you spin counter clock wise when you turn the wheel over???
Damn bro that's crazy