The apparatus decribed here and shown on the left may be used to determine the value of g. It consists of an electromagnet that holds an iron ball suspended above a hinged plate. A circuit is linked to the electromagnet and the hinged plate, through a small magnet that normally holds the plate in a horizontal position and closes the circuit. The timer operates in such a way that when the current to the electromagnet is switched off, the ball starts to fall and at the same time, the electronic timer is switched on. When the ball hits the hinged plate, the contact is broken and the timing circuit is switched off.

In this way, one can accurately determine the time taken for the ball to fall through a height h (measured from the bottom of the iron ball. The timer is accurate to 0.001 s. A series of experiments were carried out, measuring h with a steel ruler, and determining the time taken for the ball to fall. The results are tabulated below.

The values of g were calculated from g = √(2h/Δt²) The tabulated values give an average value of g = 9.81 m.s‾².