Henry Ernest Dudeney/Modern Puzzles/209 - A Wheel Fallacy/Solution

by : $209$

 * A Wheel Fallacy
 * Here is a curious fallacy that I have found to be very perplexing to many people.

Solution
Fairly obviously, the inner wheel does not only roll along $CD$ but slides along it as well.

Suppose the inner wheel rolls along $CD$ without sliding.

Then the bottom of the upper wheel move backwards in the same way as the bottom of the flange on a railway wheel, as analysed in $211$ - Another Wheel Paradox in this collection.