Consider these four situations:
- a tennis ball falling on a wooden floor
- a tomato falling on a wooden floor
- a book falling on a wooden floor
- a tennis ball falling on a soft mattress Why only in the first situation the object bounces?
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$\begingroup$ In the case of the tennis ball on the wooden floor the collision is elastic, and in the others the collision is inelastic. The tennis ball will flex, and push itself up. The tomato will flex but lacks elasticity to propel it back up. $\endgroup$– user16217248Jun 22 at 19:01
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$\begingroup$ @user16217248 thanks, but what does the kinetic energy of the object in each situation change into? $\endgroup$– Piotr HJun 22 at 19:21
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$\begingroup$ Ball: Back into the ball, as upwards velocity. Tomato: If the tomato ruptures, sideways velocity of the tomato pieces. Book: Sound. Tennis ball on mattress: Infrasound I am guessing. $\endgroup$– user16217248Jun 22 at 19:28
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3$\begingroup$ Does this answer your question? Why the rubber ball bounced higher than the glass ball? $\endgroup$– ChemomechanicsJun 22 at 19:48
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$\begingroup$ @user16217248 thanks, in case of a mattress I assumed it would be the elastic energy of the mattress and then it would transform into heat $\endgroup$– Piotr HJun 22 at 19:55
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1 Answer
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When the tennis ball hits the floor, the floor doesn't give much. Most of the energy is work done on the ball, becoming stored elastic energy. This immediately is converted back into kinetic energy as the tennis ball springs back into shape and propels upwards. A small amount of energy is lost in sound waves in the air and floor, or heat.
When the tomato hits the floor, the tomato deforms, and the work required to deform the tomato is the force required to do so times the distance of the deformation. Tomatoes are not elastic, so the energy does not go back into kinetic energy, but likely goes into heat, the same way that if you bend metal repeatedly it gets hot.
When the book falls, assuming it falls flat, it momentarily traps air underneath which is forced away at a high speed as the book makes contact with the ground. In this case, much of the energy leaves as sound. A book falling on the floor this way is much louder than a tennis ball or tomato.
When the tennis ball falls on the mattress, the mattress deforms and compresses a non-negligible amount, resulting in air in the room moving in to fill the space, and when the mattress rebounds, the air is moved. This takes sufficiently long that the resulting sound wave is not audible and is infrasound.
