Eli5: An inertia demonstration experiment tells that: “A coin is placed on a smooth card which serves as a lid on a glass. When the card is pulled suddenly in the horizontal direction the coin falls into the glass.” But when we pull the card slowly and gradually, the coin will go with card. Why?

Question

Eli5: An inertia demonstration experiment tells that: “A coin is placed on a smooth card which serves as a lid on a glass. When the card is pulled suddenly in the horizontal direction the coin falls into the glass.” But when we pull the card slowly and gradually, the coin will go with card. Why?

In: 0

Answer 1

When the card is pulled slowly, the coin moves with it because of friction between the coin and the card. But there is a maximum amount of frictional force that can be applied before the coin will start to slip.

Force is equal to mass times acceleration, so the faster the card is accelerated, the greater the force that would have to be applied to the coin in order for the coin to move with it. If the card is pulled fast enough, this force becomes greater than what friction can apply and the coin will be left behind.