All dense objects in free fall have the same acceleration, which is known as the acceleration due to gravity. The value of acceleration due to gravity is approximately 9.80 m/s2. In this experiment, a vertical stand with an electromagnet at the top for holding and then releasing of the falling body, called the plummet. The plummet falls between two vertical wires, a spark timer applies a high voltage across the two wires at uniform intervals of 1/60s. The resulting spark jumps the gaps between the plummet and the wires, passing through a strip of heat sensitive paper. The spark leaves a visible mark on the paper.
We then measure the distance between successive marks on the paper. Knowing the time interval between sparks, we can calculate a set of average velocities for the plummet using the definition:
It can be shown that the average velocity during any time interval is equal to the instantaneous velocity at the midpoint in time of the interval, provided that the acceleration is constant during the time interval. The set of average velocities described above may then be treated as a set of instantaneous velocities. Once velocities are known at definite times, we can find the average acceleration by using the definition:
When acceleration is constant, the following equation can be used:
v = vo + at