一個濕的網球 , 同一個乾的網球 , 邊個比較彈?

The dry tennis ball would rebound better

On impact, the water acts as a soft cushion to a wet tennis ball. Hence, the tennis ball has to push away the water before contacting with the ground/wall. This would lengthen the time of impact and thus reduce the impact force. The collision is therrfore inelastic (as compared with an almost elastic collision of a dry tennis ball)

In an inelastic collision, part of the energy of the ball would be dissipated to heat up the splashing water. This leads to the rebounded wet ball possesses less energy than a dry one/

Therefore, the collisionA dry tennis ball can be bounced higher than a wet tennis ball. It is not because a wet tennis ball is heavier than the dry one. It is because the water on the tennis ball has absorbed some kinetic energy from the tennis ball.

A dry tennis ball can be bounced higher because a wet tennis ball is heavier than the dry one.