Transcription
In 1982, every single person got this question wrong. Take a look at the problem. You have two identical coins. If you take the first coin and roll it around the outside edge of the second coin without slipping, how many full spins will the first coin make before it gets back to where it started?
Well, since both coins are the exact same size, your common sense says that should just be one spin. The distance around the first coin perfectly matches the distance around the second coin, so it should just roll one time. And that is exactly what the test makers believed. So, they marked one as the correct answer, but they were wrong.
Only three students in the entire country realized that the real answer is actually two. Here's why. When a coin rolls along a flat, straight line, it only spins one time for every lap it makes. But, when a coin rolls around a curved object, something strange happens. Because the coin is not just rolling across a surface, the entire surface is curving underneath it. Because the coin is traveling in a big circle, the center of the coin is actually tracing out a much larger invisible path in the air. This forces the coin to complete a second full rotation just to keep up with the curve. And you could test this yourself. Put two quarters on a table and slowly roll one around the other. Keep your eye on the president's head, and you'll see.