Balls

[GazzaJAnimal]

I've been meaning to post on this subject for a while, but I've been busy. When tournaments come around we always get commentators and summarisers passing comment on how the match balls are getting lighter and that they cause problems for goalkeepers.

This, to me, doesn't compute. I have consulted the law book and there isn't a great deal of leeway in either the weight, size or pressure of a football. The circumference is not more than 70cm (28 in) and not less than 68cm (27in), a difference of 2cm. The weight not more than 450g (16oz) and not less than 410g (14oz) at the start of the match, a difference of 40g. The difference in pressure is a little more being 600 - 1100 g/cm2 or 8.5 lbs - 15.6 lbs/sq. in.

So not a lot of difference in allowable variations there. What's everyone else's thoughts?

 

[Mike]

Whilst it may not seem a lot, a small amount probably makes a lot of difference. For example, the weight can change by 10%, the circumference by 3% and the pressure by 83%. Whilst they are small it probably makes quite a large difference if they are all at their smallest/largest.

 

[MattyontheWhistle]

Try kicking two balls, one inflated to minimum, and one inflated to maximum pressure you can feel a huge difference, and it makes a big difference to the balls aerodynamics as well - and that's just adjusting the pressure.

The covers material as well makes the balls 'feel' much lighter when kicked - the newer balls with a 'softer' cover (we have some Nike ones at the junior club I work at) are much preferred by the kids because 'They are softer coach" - well actually they aren't. I have inflated one of them to full 1100, and left one of the older balls at 8oo - and the Nike was still 'softer' according to the kids.

I think commentators saying they are 'lighter' is just another case of them not knowing what they are talking about.

 

[Brian Hamilton]

If the ball is correctly inflated, there's a number of factors which influence the flight including the force of contact, the point of contact in relation to the valve, the area of the ball which has stitching (therefore affecting its proximity to a perfect sphere) the strength of the outer layer of the ball (my Physics A level from more than 30 years ago wants to say tensile strength?) which affects how much the ball will compress on being struck, the wind direction and also whether the ball is wet or dry.

if you change the weight of the valve, the the amount of stitching, the nature of the outer layer, then these will make the ball move differently from another ball in the same environment.