This is a double pendulum apparatus to investigate the fundamental properties of pendulum. The length of the pendulum can be varied using the steel balls to observe the effects. It can be mounted to any retort stand upto 13 mm rod diameter. Two steel balls are provided with the apparatus. With this apparatus, the qualitative studies of periods of steel balls with individual string lengths, frequency and beats can be done. A stopwatch is required to examine these ideas quantitatively. User instructions are provided.