I am going down to the club solely to lose weight by sitting in a Tenko-styled sweat emporium.
The hot tin roof certainly adds a couple of degrees to the on court temperature, but the leagues must go on – and be finished by mid August.
This months little fact is focused on squash balls and how they react to hotter temperatures. We are concerned that like the M25 balls may start melting in the hot house that is Christophers. Let us know
Why does a squash ball bounce higher when it’s warm?
To understand this we need to do a little physics. Ready? In order for a solid material to be deformed, work has to be done on it. For that work to be done, energy must be expended (in the case of a squash ball, it is hit by a racket). Some of this energy is dissipated (as heat, etc.), but some is stored in the deformed material and is released when the material relaxes. The extent to which a material stores energy under deformation is called ‘resilience’. Some materials (like sprung steel) store a lot of energy and are described as having high resilience; others (like putty) store very little and therefore have low resilience.
Squash balls, being made of a rubber compound, are of fairly low resilience. Unfortunately, as we know, the lower the resilience of an object, the higher the proportion of the energy used in deforming it must be dissipated. When a squash ball hits the racket strings and the wall and floor of the court, some of this energy is transformed into heat in the strings, wall, floor, and surrounding air and some into sound, but most of it becomes heat in the ball itself. This has two effects: the air inside the ball (which was originally at normal atmospheric pressure) effectively becomes ‘pressurised’, and the rubber compound from which the ball is made becomes more resilient. For both these reasons, the ball bounces higher. Obviously, the ball does not continue indefinitely to heat up; eventually equilibrium is reached where heat loss to strings, wall, floor, and air is equal to heat gained from deformation. This point is normally at around 45oC, which is why the WSF’s rebound resilience specification is calculated at that temperature. It also explains why squash balls are designed to have too little resilience at room temperature and therefore why they need warming before play.