It allows the user to use different combinations of total energies and masses. The mass is raised to the appropriate height and is dropped and bounces off an energy absorbing surface. The applet demonstrates conservation of energy, conversion of potential energy into kinetic energy, and that objects of different mass when dropped from the same height, impact the ground at the same velocity. Potential energy exists whenever an object which has mass has a position within a force field. The most everyday example of this is the position of objects in the earth's gravitational field.
Kinetic energy exists whenever an object which has mass is in motion with some velocity.