Re: squash ball question

[brian whatcott <inet@INTELLISYS.NET>]

At 22:13 10/18/00 +0200, Mark Sylvester wrote:
> I have a student doing a project on squash balls: these are rather soft
> rubber balls which don't bounce very well, but get more and more elastic as
> their temperature is raised through being slammed around the court.
>
> He's measuring the coefft of restitution at different temperatures, and
> getting something like a linear graph. The problem is to produce an
> explanation. He needs to be pointed in a fruitful direction, but I find
> myself stuck. It seems clear that it's the air inside the ball that causes
> this behaviour, rather than the rubber, but how to relate this to the
> dissipation that occurs during a bounce...?
>
> I'd appreciate any ideas.
>
> Mark

I am not the first to mention it, but the change in properties of
any enclosed air with temperature can be expected to be roughly
proportionate to absolute temperature:
taking 20C and 100C the change is 373/293 = 127%

The change in restitution of the rubber material
 can be 71/45, 47/37, 63/33, 67/35, 50/9 for a similar temperature
range, depending on the material in question
(natural rubber, butadiene-styrene copol.,butadiene acrylonitrile
 copol., neoprene,  butyl respectively according to the rubber
company: apt eh?)
These ratios amount to 158%, 127%, 191%, 191%, 555%

Hence, except for a butadiene-styrene copolymer ball, the rubber
 is likely to contribute the major temperature dependence.

Or as Professor Feynman pointed out in dramatizing the problem of
making a rocket case in pieces for shipment from a remote, but
senatorially sponsored state, pork-barrel-wise: a cold rubber
seal may not flex the way you'd want it to flex.

Or with twenty twenty vision over the shoulder: "My kingdom for
a miserable imbedded heater wire."



brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!