Many people have done experiments on what makes a baseball bounce
better. Heating them does make the balls bounce higher in general,
although the actual behavior of the ball when heated depends on what it
is made out of. Tennis balls, basketballs, racquetballs, etc. are all
easier to think of than baseballs because they are hollow with air
inside. A baseball is made from a small rubber core with many layers of
yarn wrapped around it, and has a stitched leather outside. I suspect
(I haven't done the experiment) that when the ball is warmer, the
components are less stiff. If you have ever tried flexing leather boots
on a cold, cold day, you will notice that it isn't as easy as on a hot
day. There are different kinds of stiffness in the world -- there are
springy things that give you back the energy you put in them (like
rubber and springs, and they bounce well if they are stiff or not), and
then there are things that just deform and stay that way, like leather
and yarn. I suspect that the stiffer leather and yarn just absorb the
mechanical energy of the bounce more because it is harder to flex them
when cold.
The humidity (of the air) should have almost no measureable effect
on the bounce of a baseball (higher humidity may increase air drag for
those long fly balls however). It will take a long time for a change in
the air to "soak into" the ball because it is so tightly wound and
sealed up. If you keep your baseballs in a bucket of water overnight
however, my guess is that they will not bounce as well the next day
(again, I have not done the experiment, except to have played with some
old, torn softballs on a rainy day and being disappointed in their
performance). The yarn will soak up lots of water and it will squeeze
out of the threads when the ball hits the ground or bat, robbing the
ball of some energy to do all this. But for normal humidity conditions
I suspect that the mechanical properties of the yarn will be affected
only a very tiny amount, and that you will have to wait a long time
before the increased water content of the air shows up inside the ball.
Tom
(published on 10/22/2007)
