Mystery of the wheel

Sticking to the rim of the wheel crawling a piece of colored paper and watching it move, you will see a strange phenomenon: When the piece of paper runs down to the lower part of the wheel, we see it quite clearly, while on the upper then it turns so fast that we can't recognize it anymore.

When the wheel moves forward, we have the passage: AA '-> BB'

Therefore, it seems that the top of the wheel moves faster than the lower part. Similarly, observing a running wheel, we also see the above spokes blending into one continuous strip, while the spokes on the bottom are separate.

So what is the mystery of this phenomenon? The answer is, the upper part of the rolling wheel is indeed moving faster than the lower part. Why? Each point of the rolling wheel performs at the same time two movements: turning around the shaft and moving forward. Therefore, there is movement synthesis here. This combined result is not the same for the top and bottom of the wheel. Above, the rotation movement adds a smooth movement, while the reverse is the opposite. Therefore, for the observer, the upper part of the wheel moves faster than the lower part.

To prove it, we can do a simple experiment like this: Plug a stick to the ground on a par with the axis of a stationary wheel. Use chalk to mark the highest edge (A) and the lowest (B) of the wheel. Now, push the wheel a little right so that the axle is about 20-30 cm away from the stick and notice how the marks have moved. You will see the above A move more than the lower B sign (see image above: section AA '> section BB').