Algodoo

Another way to show this is to attach a small circle with a tracer on the tire. You can then plot the speed of the small circle. The tracer will show the path and the plot will show the speed of one small element of the wheel.

Yes, I am aware. But I thought I explained it well enough, and to be honest, I was too lazy to make that.

I believe it is called a "cycloid" curve.

I agree, your scene stands well on its own without any added info.

I hope other people will understand too.

mold999 said - "believe it is called a "cycloid" curve."

You probably meant "epicycle". I made a scene a few weeks ago that demonstrates the epicycle motion: http://www.algodoo.com/algobox/details.php?id=66948

You could see this demonstrated in real life by placing a small light on the rim of a bicycle wheel, and stand off to one side as the rider goes by you (at night of course).

Edit - "cycloid" is correct. I looked it up on Wikipedia!