Sunday, Funday


Technical Support
Staff member
Consider a wheel within a larger wheel; a car tyre and its wheel hub is an example most people are familiar with.

As we roll the tyre through one revolution, it will have traversed a distance of X, which is the same as its circumference. Obvious stuff so far.

Now look at the inner wheel. It has also traversed a distance of X while completing one revolution but that distance is much greater than its circumference.

Go Figure!

Image and intrigue courtesy of


Senior Member
And if both diameters were on rails and there was no slippage then it wouldn't rotate very far at all.

The hub would travel though a much lesser distance for one revolution. It's all a matter of Revolution Euducation ! :)