Soccer balls

Question: I am helping some students who want to do a project involving the physics of kicking various kinds of soccer balls (They are 10 -11 years old). I wanted to help them formulate a hypothesis and find other experiments along that line that might help in their project.

Answer:

Are the balls soccer (round as in the UK) or roughly elliptical (like American football or UK rugby)?

It may not matter so I will give you some ideas that ought to fit either.

1. Kicking or throwing is a really difficult thing to measure because the force involved in the muscles is so hard to determine. There is an experiement that we do here that could measure that but it involves momentum and would probably be much too hard for 10 -11 year olds. Anyway I will describe it below and you could maybe modify it if you think it is worth it.

2. Kicking a football
This classic experiment is used consider the momentum change of the football and hence the force used to kick it. A piece of aluminium foil is taped to the football and another piece is fixed to the shoe of the kicker. The foil on the foot is connected by a long lead to one of the start terminals of a scaler, while the other terminal is connected by another long lead to the foil on the ball. The ball is placed on the edge of the bench a known height above the ground and kicked off horizontally - the scaler recording the time for which the foot was in contact with the ball and the connecting wires breaking as the ball moves off. The horizontal distance travelled is measured together with the time taken to hit the ground and from this the horizontal speed of the ball is found. From the values of mass (m), velocity (v) and time (t) the force used to kick the ball can be found. I have tried it outside with a hockey ball. This works fine if the wires are allowed to separate after the ball has moved a short distance and somebody hangs onto the scaler!

Brief theory

Horizontally s = uT and Ft = mu Vertically h = 1/2(gT²) where t is the time of contact between the foot and the ball and T is the time taken for the ball to reach the ground having fallen a height h and travelled horizontal distance s.

Age range: 14-18 (as I said – usually done with older students)

Apparatus required:
Football Scaler Crocodile clips Long leads Aluminium foil Measuring tape (10 m) Tape

3. General projectiles
Try using rubber bands to simulate muscles and get them to measure the range of various projectiles. You can vary the mass of the projectile, the angle of projection (by firing the projectile up a ramp) and the force needed (simply by investigating the properties of the rubber band). Look up the Roman siege engines used in Europe around the year 30 AD. Direction is very important – you can kick a ball really hard but if it is just going horizontally it won't get far before it touches the ground.

4. Discuss the effects of air on the path of the ball. Compare it with golf balls. Why ere there dimples in a golf ball – it makes them go further. Balls swerving in the air – what we call a banana shot. Try kicking balloons – they are much lighter than a soccer ball but won't get far.

5. Principle of impulse – the longer your foot is in contact with the ball the further it will go. Try kicking balls when standing at different places relative to the ball.

6. Properties of your body that affect how far you can kick. It is not always possible to give it the biggest "boot" by applying the principles of Physics alone!

7. There are a number of very good CDs that show slow motion clips of jumping, throwing and collisions. A very good one available in the UK is called Multimedia Motion. Aimed at older students there are some really good clips. Your children might find it useful with help.

8. Use a plastic tube as a blowpipe to project marbles at varying angles (N.B you need to fit a metal rod across the end nearest your childrens' mouths to stop them swallowing the marble!

9. You could arrange a competition between the children to see who can kick a ball the furthest. From the ground or dropped from their hands.

10. Could you video their attempts and analyse what they do?

11. How about going to a local soccer match or indeed watching matches on a video to look at how far football players can kick.

12. Leverage and the shape of the human leg. Straight legs or bent legs.