## The Rolling Coin Paradox that drove me Crazy!

June 4, 2020

The MindYourDecisions blog (Video below) presents the PARADOX beautifully.

Now consider the example of the coin rolling around a coin of the same size. Intuitively we think …’OK. Same circumference, so the coin will rotate once as it rolls around a same-size coin. But this doesn’t happen. It rotates twice.

# TWICE!

This observation is SOOOOOOOO counterintuitive we have to know why?

# Why?

Mr. MindYourDecisions doesn’t explain why this happens. The answer is interesting. The relevant point in the ROLLING COIN PARADOX is the centre of the rolling coin. The rolling coin rotates about that point. And that centre (the red dot in the gif below) moves through a circle twice the circumference of the stationary coin. It is much easier to understand when you see it. (Below)

### 4 comments

1. […] Just another WordPress.com weblog « The Rolling Coin Paradox that drove me Crazy! […]

2. Very good animation and explanations.

• Thanks Paul

3. […] ROLLING COIN PARADOX HERE […]