As I just learn about the rolling motion which is the combination of pure translation and pure rotation. The top portion of the rolling body has the speed of double speed at the center of the object while the bottom one has no speed
Also, it can be view as the rotation that take the axis at the bottom portion
However, comparing both of those 2 explaination with the thing I see in real life, in this case, the rolling wheel, and in dynamical analysis, why the bottom having no speed can move?
For example, a rolling wheel on the street, let say the bottom of the wheel has no speed but the wheel is a rigid body and as time gone by, it move a distance so the bottom must have speed to move but as the definition the bottom have no speed which mean it is stationary so what make its displacement if there is no speed
Best Answer
The bottom of the wheel is a different part of it at every moment. If you follow a particular point on the wheel, you'll see it moves down and slows in forward motion until it touches the surface at zero speed and immediately starts to move up and accelerate forward again. Up to twice as fast at the top to catch up and get on the forward side again and then it descends and decelerates and the cycle repeats.
This animation from Wikipedia shows the path taken by arbitrary point on a wheel quite well:
The path is called Cycloid.
In reality the bottom of the wheel indeed does not move. Otherwise it would be skidding and have a poor grip on the surface since static friction (force preventing two surfaces from starting to move relative to each other) is higher than dynamic friction (force opposing skidding of two surfaces).