# Rolling coins     4.09 (11 votes) Loading... You have two coins of the same size and roll one around the other.
How many times does the rolling coin roll around its center?

Hint: It’s not one!

What if the coins were different sizes?

### 9 thoughts on “Rolling coins”

1. twice 🙂

2. I believe it is called Copernicus’ theorem, or some variation of it.

3. it’s 2 revolutions…..for diff size the ans will be r1/r2+1…..where r1 and r2 are radius of static and rotating circles respectively.

4. umm 2 i gess i am dumb lol 🙂 LOL ON ME HAHAHAHAHAHAAHAHAHHAHAHHAHAHAHAHAHHAHAHAHAHAHAHAHAHHahahahahahahahhahshhhhahahahahahahahahahahahahahahah

5. First I think was Pi, but is impossible to do a GIF of that! 😆

6. This is pretty easy. Answer is 1.5

Because when the outer coin roles, it makes a bigger circle outside with diameter of 2*r1+r2 or 3*r1 if they are equal size. The circumference of bigger circle will be 2*pi*(3*r1/2) and for outer coin we have 2*pi*r1 . If we divide these two we get the answer which is 1.5

7. Zero!!! It is rolling around the OTHER coin’s center!! :]

8. online science

Visually it seems one to me!

Mathematically it is very very very confusing.

9. Before I answer, does the coin have a milled or a plain edge Coin Terminology ? 😈 as this may affect the roll 