Friction is a sticky force that appears when 2 objects rub against each other. If you push or pull slowly friction helps pull or push the tower along with the bottom coin. If you push or pull quickly, the coins still rub, but the friction force doesn't have time to get the stack moving.
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Answer:
Friction is a sticky force that appears when 2 objects rub against each other. If you push or pull slowly friction helps pull or push the tower along with the bottom coin. If you push or pull quickly, the coins still rub, but the friction force doesn't have time to get the stack moving.