### Re: Does the temperature of a baseball affect it's rebound rating?

Date: Fri Jan 28 10:31:21 2000
Posted By: Tom Cull, Staff, Clinical Sciences MR Division, Picker International
Area of science: Physics
ID: 948315785.Ph
Message:

I cite one of my favorite references The Physics of Baseball by Robert K. Adair, which discusses briefly the
effects of temperature on the distance a ball will travel. Adair, retells of legends of manager John McGraw storing baseballs on ice up to a few hours before game time to give to the umpire when the visiting was batting. Nowadays, the umpires are in possession of the game balls about two hours before game time and are not sorted. Baseballs are stored at nominally room temperature and only in play for a little while, so chances are that the ball doesn't cool down too much on cold day , but could warm up considerable on a hot day.

A colder ball will have a lower coefficient of restitution (COR) (bounce/spring/elasticity) which is a measure of its ability to retain kinetic energy after a collision. A lower coefficient of restitution will result in more energy loss at contact, and therefore less distance travelled by a batted ball. Conversely, a warmer ball will have a higher COR. Adair reports that a batted ball that would go 375 feet at 70 oF will travel 3 feet farther for every 10oF increase in temperature and will travel 3 feet less for every 10oF drop in temperature. Remember this the ball's temperature. It will take some time for the ball to achieve ambient temperature.

The effect of temperature is much more pronounce with a tennis ball. I used to play tennis quite a lot with a friend of mine. We would play in any kind of weather --Tennis in St. Louis January.
The tennis ball would nearly freeze in 5 minutes or so when the temperature was freezing or below. We would rotate tennis balls and keep a couple warm to use. We actual had a ball crack from its loss of elasticity. When it was hit by the racket instead of compressing and bouncing back, it simply cracked. Part of the reason is that a tennis ball is hollow, so only the rim has to get cold for the effect to occur. A baseball cork center is effectively insulated by the yarn winding. The freezing effect is also quite obvious with a typical plastic core softball.

Actually the storage conditions of the ball can have a significant effect. A baseball stored in an extremely humid environment will be heavier from absorbed water and will have lower coefficient of restitution when hit.

Also one should consider the increase in discomfort level from bat vibrations. A cold bat will resonate more on contact with a ball away from the sweet spot of the bat. Batter's will complain of "bees in the hands" more frequently on cold days. This effect is especially noticeable in little kids playing ball in the early Midwest spring. It becomes a "right of passage" to get your hands stung and to keep swinging.

If you are interested, several previous MSN responses are available on ball-contact sports.

Sincerely,

Tom "Ice Pack" Cull

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