A question on rotation

[BadgerBadger92]

I have heard on several sites that the bottom of a wheel or ball that’s rolling is not moving at all. How does this work? I can’t quite wrap my head around this one lol

 

[hutchphd]

I have heard on several sites that the bottom of a wheel or ball that’s rolling is not moving at all. How does this work? I can’t quite wrap my head around this one lol

Of course you should say "moving relative to the ground". If the cart on which the wheel is attached is moving at speed v then the wheel will rotate such that the bottom of the wheel is at 0 and the top of the wheel moves at 2v (relative to ground) ,assuming unimpeded rotation.

 

[Parthib Roy]

I have heard on several sites that the bottom of a wheel or ball that’s rolling is not moving at all. How does this work? I can’t quite wrap my head around this one lol

the bottom of the wheel acts as a instantaneous axis of rotation ,so as to simplify the part of the wheel in contact with the ground acts as a hinge on which the top of the wheel rotates

 

[Ibix]

I have heard on several sites that the bottom of a wheel or ball that’s rolling is not moving at all. How does this work? I can’t quite wrap my head around this one lol

If it were moving relative to the ground it would be sliding.

Think about what the wheel looks like if you've lifted the car up on jacks and then started it. The bottom of the wheel is moving backwards, right? Now if the car is going forwards, and the bottom of the wheel is going backwards, the velocities might cancel - and in fact they must cancel or the wheel would be slipping against the ground.

 

[berkeman]

I have heard on several sites that the bottom of a wheel or ball that’s rolling is not moving at all. How does this work? I can’t quite wrap my head around this one lol

Have a look at this article about the Cycloid motion of a point on a wheel:

https://en.wikipedia.org/wiki/Cycloid

https://upload.wikimedia.org/wikipedia/commons/6/69/Cycloid_f.gif

 

[BadgerBadger92]

Have a look at this article about the Cycloid motion of a point on a wheel:

https://en.wikipedia.org/wiki/Cycloid

https://upload.wikimedia.org/wikipedia/commons/6/69/Cycloid_f.gif

View attachment 372134

Do you know of any good videos about this? I learn best visually and from videos.

 

[berkeman]

Do you know of any good videos about this? I learn best visually and from videos.

I did this Google Images search and got good hits: