Force used to kick a football

In this demonstration, students use impact-time and distance measurements to determine the size of the kicking force for a football.

Learning outcome

Students can calculate the average force on a ball during a collision using mass, speed and impact-time data.

Apparatus and Materials

• Scaler electronic timer accurate to 0.001 s
• Round football (rugby type not suitable)
• 30 cm flexible leads with crocodile clips, 2
• Stopwatch or stopclock
• Balance (to measure mass of ball)
• Aluminium foil square, 15 cm by 15 cm
• Aluminium foil square, 7.5 cm by 7.5 cm
• Sellotape
• Plasticene

Health & Safety and Technical Notes

In this demonstration, the ball is kicked horizontally off a laboratory table. You will need a space of about 5 m or more (e.g. a large laboratory or a corridor) and take care to aim the football so that it does not cause damage.

For the timing circuit you will need long leads connected via crocodile-clips to aluminium foil taped to the football and foot. Use leads that are a loose fit into the timer inputs so that they will come out easily in the event of an accident. Also ask for a volunteer to hold the timer to ensure it doesn’t leave the bench.

Procedure

1. Place the ball on a laboratory bench and use three small lumps of plasticene to stabilize it.
2. Measure the height h of the bench.
3. Tape a large foil to the football and a small foil to the toe of your kicking foot.
4. Use crocodile clips to connect one end of the long leads to the foil and the other end into the ‘timer input’ sockets.
5. Stand on the bench and kick the ball horizontally from a standing position with a medium force (more vigorous kicks can be used out of doors to show the longer time of contact).
6. Measure how far the ball travels horizontally s before it hits the floor.
7. Read out the time of contact T of the ball with the foot from the timer.
8. Find the mass of the ball, m, using a balance.

Teaching Notes

The connection with the ball will break during the demo. Provided that this doesn’t happen during the period that ball and foot are in contact you should obtain consistent results.

After the ball leaves the foot, it behaves as a projectile. It’s time of flight, t, can be found from the height of the table using:

t² = 2hg , where g is the acceleration due to gravity.

The launch velocity of the ball, u, can be found using u = st

And hence, the magnitude of the average kicking force using F = muT