# Q & A: Does a hot or cold tennis ball bounce higher?

Q:
do a tennis ball bounces higher hot or cold?
- Abrianna ivey (age 13)
Thomson, GA U.S.A
A:
Hello Abrianna,

This is a very interesting question and I wish I knew the complete answer.  I am a tennis player and have often thought about it but never got around to investigating it thoroughly.  I once put a can of tennis balls into the freezer and discovered that they didn't seem to bounce as well until they warmed up.  But that was a subjective observation and not a real measurement. Other things affect tennis ball bounce and also flight distance.   I once played tennis in Snowmass Colorado, altitude 10,000 feet.  The balls seemed to sail forever and I was always hitting them out.   The 2010 Davis Cup match between USA and Colombia is being held in Bogota at an altitude of 8662 feet.  Apparently they use so called "low pressure" tennis balls in their matches.  Some of the players have commented about it.

Now, there are several things that would affect the bounce.  Probably the most important is the so-called coefficient of restitution, which itself depends on the internal air pressure and the elastic properties of the outer covering of the ball.   Many materials have temperature dependencies in this elastic coefficient.  The atmospheric air pressure will affect the resiliency to a small amount, but affect the air resistance in flight to a greater amount.

As an experimental physicist, and trying to be a bit more thorough than my previous attempt, I would take a brand new can of three balls, put one in the  freezer, let one stand at room temperature, and put one in the oven at a temperature of 150o F.  After they have reached equilibrium temperature stand on a chair or ladder and drop them, one at a time, onto a hard surface;  concrete or tile is probably best.  You may need a helper to judge the height of the bounce.   Do it several times and average the results.