1. Set up a vertical electric circuit with a switch, timer, electromagnet and trapdoor and attach a ball bearing to the electromagnet 2. Measure the h from the ball bearing to the trapdoor 3. Flick the switch to start the timer and disconnect the electromagnet 4. The ball will fall and knock the trapdoor down, breaking the circuit which stops the timer- record this time 5. Repeat 3 times and find an average, then repeat at different h 6. Plot a graph of h against t^2 to find 1/2g as the gradient