# Soccer Ball Compression

1. Feb 5, 2009

How much should a soccer ball be compressed between 2 objects for it to be safe for the soccer ball but also to maximize the friction between the ball and the objects. The values used for this should be the official circumference of 70 cm and a pressure of 13.5 psi.

2. Feb 5, 2009

### reasonableman

Well, static friction is modelled as proportional to the force between the two surfaces involved. So to maximise friction you need to maximise the force.

Your 'safe for the soccerball' is probably going to be your limiting factor. I really have very little idea how much pressure a football can withstand. But as a tyre has about 30 psi and makes a pretty big noise if they burst I'd say you probably don't want to go above that.

I going to make some further assumptions to get a rough estimate, I wouldn't recommend basing any experiments on these calculations as they could be dangerous.

Assuming the football is a cube, and keeps a constant cross-section (isn't physics great). Compressing it so it's 2/3 it's diameter in the compression direction would reach 27 psi. The 2/3 arises because the pressure you're referring to is pressure with reference to atmospheric, rather than absolute pressure.

3. Feb 5, 2009

That helps alot thanks.

Does anyone know of someone doing an experiment much like this?

4. Feb 5, 2009

### Staff: Mentor

No, but the critical thing here is the pressure. 13.5 psi is the inflation pressure of the ball, but it isn't the pressure that it can safely withstand (burst pressure). If it were the burst pressure, it would burst the first time someone kicked it. So what you really need to know is the burst pressure. Then when you compress it between two plates, you use geometry to find the new volume and pressure of the ball when a certain force is applied. That's not a simple geometry problem, but it is doable.

5. Feb 5, 2009

### reasonableman

There's a small chance that a football manufacturer has to do a bursting test for some safety reason...other than that I can't really think why anyone would want to do it!