Secondary Science

For a more interesting way to teach physics, how about a paintball session with an unusual experiment thrown in? Paintballing is an activity where players use gas-powered rifles to project plastic coated paint pellets at their opponents; the pellets explode on impact, making a gooey mess.

A paintball pellet travels fast and, if you choose to play a game of paintball with your pupils, you will quickly discover that teachers are the prized targets. A neat experiment is to try to find the speed of the paintball pellet as it leaves the barrel.

An interesting way to establish the speed of the pellet is to use a simple electric circuit that includes a capacitor. This is a component that stores electric charge. The paintball pellet can cause a disruption in the circuit that will cause charge to leave the capacitor.

By measuring how much charge remains in the capacitor one can establish how long the pellet was within the circuit. If we know how long the pellet was travelling between two points then we can calculate its speed. It happens fast and we need to use an unusual method. A normal stopwatch would be too crude for this job.

If you are a science teacher you may already know the theory behind this experiment; you may have seen similar problems in a textbook. The circuit diagram and discharge graph is a favourite for examiners and can be found in many textbooks. If you are a non-specialist, the experiment is similar to measuring time using an hourglass that lets electric charge flow away instead of sand.

Your pupils will find that they will need to work in an environment that is not ideal. They will learn that some problems need ingenious solutions and they will need patience to create the circuit. Teamwork and communication skills will be important to complete their task. Most of all, they will be inspired by a fascinating, challenging and practical subject.

The paintball is fired through two tin foil switches. When the first switch opens the capacitor starts discharging. When the second switch opens the capacitor stops discharging. The time of transit can be found using the capacitor discharge equation. Once the time of transit is found, the velocity of the pellet is easily determined.

Simon Houghton teaches physics at Millfield School in Somerset

TIPS FOR A PAINTBALL EXPERIMENT

- Find a local paintballing firm that is willing to help. The experiment does not require much ammunition, although it will take time to complete.

- You should be provided with full protective equipment: a mask, overalls and gloves.

The supervisor and teachers will need to ensure that the children follow all safety advice carefully.

- Try the experiment before the event to ensure that you can solve all potential problems.

- Promote your ideas to willing pupils. It is a good idea to run a theory session beforehand to ensure that pupils understand the science involved and that they are adequately briefed.

- Make absolutely clear that, during the experiment, all pellets must be fired into a safe area. This is a tricky experiment without the problem of incoming ordnance.

- Play paintball afterwards. Paintball is lots of fun, but you need to warn pupils that, if they are hit, it will sting.