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Q & A: Ping-pong balls bouncing higher

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Most recent answer: 06/28/2008
Q:
why does the ping pong ball bounes higher then other balls?how?
- nikki (age 11)
epsom normal primary, new zealand
A:
Hi Nikki,

The height to which a ball bounces depends on several factors:

1) The height from which it is dropped,
2) Whether it was thrown down or just dropped and how hard it was thrown,
3) How much energy is lost in the ball during the collision with the floor
4) How much energy is lost in the floor during the collision with the ball.
5) Some slowing from air resistance (but not so small if the ball is a balloon or made from styrofoam for instance).

Assuming that the experiments are properly "controlled", that is, everything but the ball type is the same, then what is different is how much energy is lost in the ball. Ping-pong balls are very stiff and springy -- they lose only a small fraction of their energy when they bounce on a hard surface. On a soft, squishy surface, the ping-pong ball may bounce less well (but then again, the other balls may bounce less well also). Some surfaces are very complicated, like a mattress. If you drop a ping-pong ball from a meter’s height on a mattress, it will probably lose almost all of its energy in the cloth and padding and not bounce much at all. If you drop a basketball or a heavy steel sphere, then the mattress springs become more important and some energy will be returned to the ball and it will probably bounce higher than the ping-pong ball. But against a hard surface, ping-pong balls do very well (and if the surface is very hard and solid, the steel sphere might do even better, if it doesn’t chip or break the surface first, as it might if the surface is made of concrete or tile).

Tom

(published on 10/22/2007)

Follow-Up #1: That's the way the ball bounces

Q:
WHY DOES A BALL BOUNCE HIGHER ON A HARD SURFACE THAN A SOFT SURFACE?
- jayla (age 11)
baltimore , md us
A:
I’m a tennis player and I know from experience that on a ’hard’ court, asphalt or concrete, the ball bounces with more ’oomph’ than on  a ’soft’ surface, like a clay court.   The reason is that the ’soft’ surface gives a little and absorbs some of the energy of the ball.  (In technical terms it is called an ’inelastic collision’.)  Having less energy, the ball doesn’t bounce as high.

LeeH

That answer works well for a nice bouncy tennis ball. A very non-bouncy ball, say a lump of clay, will bounce better on some soft surface like a trampoline than on a hard surface like concrete. Some materials, like rubber, are pretty good at returning the energy they pick up when stretched or squashed back into mechanical forms. Others, like clay, are not good at that. You get the most bounce when most of the 'give' happens in a material that's good at returning the energy. If the ball is good at it, then the best bounce happens when does all the squashing, on a hard surface. If the surface  is better at it (say some rubberized track surface vs. a dead ball) then the best bounce happens when the surface gives more than the ball.

Mike W,

(published on 10/22/2007)

Follow-Up #2: Ping pong ball bounce vs. temperature

Q:
Does the temperature of a ping pong ball make any differance to how high it will bounce
- megan (age 11)
nz
A:
For small excursions of, say 5 or 10 degrees C, around room temperature the height of bounce should not change much.   At very high temperatures the ball would probably begin to get a bit squishy and loose some of its elastic properties and not bounce so high.  I really don't know what would happen if you , for example, cooled the ball with liquid nitrogen...  might be interesting to try.

LeeH

I bet it would either crumple or crack, but that guess is no substitute for the experiment. Mike W.

(published on 06/28/2008)

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