Aboxer can hit a heavy bag with great force. why can't he hit a piece of tissue paper in midair with the same amount of force?

This is due to impulse

Explanation:

Impulse equal to mΔv and FΔt

You can set these equal as mΔv = FΔt

When a boxer punches a tissue, it is like punching a cushion or a pillow. The time that the hit takes is much grater than if they were to hit something solid. In addition, the change in velocity of the boxer's arm would be much greater when they hit a punching bag. In this equation, the greater the time, the less force that is needed.

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