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?

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Answer 1

In the second example, the force applied to the card isn’t enough to overcome the friction between the card and the coin. In the first example, it is.