Variable mass oscillator

We studied the motion of a variable mass oscillator. The mass used is a container full of sand that loses sand at a constant rate and hangs from a spring. The spring was, suspended from a force sensor connected to a data acquisition system that let us study the evolution of the system. In the underdamped regime we identified three distinct types of behavior for the system, depending on the relation between the energy loss due to the exit of mass and the energy loss through friction. The experimental results are well described by both the numerical solution to the equations of motion and our model, which makes it simple to predict the different types of behavior and to assess the relevant physical parameters involved in the dynamics of this system. (C) 2003 American Association of Physics Teachers.