Re: squash ball question

[Yifan Yu <yifany@ITS.CALTECH.EDU>]

I don't know what is actually causing this phenomenon, but I have a couple
guesses.  The air theory does have some possibility.  If the temperature
of the air inside the ball rises, so does the pressure. A fully inflated
basketball will bounce a lot better than a flat one. Also, air is very
near an ideal gas, which gives the relationship PV=nRT.  In this
situation, for a stationary ball, V n R are pretty much constant, which
gives a linear relationship between T and P.  I guess that could support
the air theory.  But i don't know what's the relationship between P inside
and how high it bounces.  So then again, that probably doesn't apply.

Another possibility is maybe temperature changes the way the molecues of
the rubber are arranged, which would affect its elasticity.  Can't think
of anything else due to temperature that could affect elasticity right
now.

One possible way of testing if the air theory is true or not is by making
a very small hole in the ball to the center.  That way, the pressure
inside will be the same as the atmosphere.  If that stops the change in
elasticity due to temperature, then it's probably the air.

On Wed, 18 Oct 2000, Doug Craigen wrote:

> 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...?
>
> Why consider it to be the air rather than the rubber?  Do you observe
> this behaviour for other air-filled balls?
>
> I know you can observe near zero restitution for some rubber balls with
> no air.  Take the ball out of your mouse and try bouncing it.  I haven't
> tried it versus temperature.
>
> > I'd appreciate any ideas.
> >
> > Mark
>
>
> \_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\
>
> Doug Craigen
>           http://www.dctech.com/physics/about_dc.html