Measuring the intensity of gravity is not as simple as it may seem. If we try to measure it by letting a body fall and measuring its acceleration, the speed of the fall makes it difficult to take exact measurements. It is simpler to measure the weight of a body with a dynamometer, but dynamometers are not usually very exact either.

   An instrument which is easy to use and is quite exact is a simple pendulum: a small heavy body (called a bob), hanging on a strong thread with little mass. We are going to see some of its properties below.