Fix on the upper part of a wheel a piece of paper. You will see a very curious phenomenon when the wheel is moving: as long the piece of paper is on the upper part of the wheel you can’t see it distinct but when it is on bottom part of the wheel you can see it very well, it seem that the upper part of the wheel is moving faster than the bottom part. As it shows in the drawing when the wheel is rolling, the distance streamed by the upper part of the wheel is bigger than the distance streamed by the bottom part of the wheel.
The explanation is very common: Each point of the wheel has two types of motions; a motion of translation with its axle, and a motion of rotation around its axle. On the upper part of the wheel this two types of motion have the same direction but on the bottom part of the wheel they have opposite directions
