Objective: Work out the local acceleration due to gravity with the help of a reversible pendulum
A reversible pendulum is a special design of a normal physical pendulum. It is able to swing from either of two mounting points and can be set up in such a way that the period of oscillation is the same from both these points. The reduction in the length of the pendulum then matches the distance between the two mounting points. This makes it easier to determine the local acceleration due to gravity from the period of oscillation and the reduced pendulum length. Matching of the reversing pendulum is achieved by moving a weight between the mounts as appropriate while a rather larger counterweight outside that length remains fixed.