This HTML5 app demonstrates the variation of elongation, velocity, acceleration, force and energy during the oscillation of a spring pendulum (assumed with no friction).
The "Reset" button brings the body of pendulum to its initial position. You can start or stop and continue the simulation with the other button. If you choose the option "Slow motion", the movement will be ten times slower. The spring constant, the mass, the gravitational acceleration and the amplitude of the oscillation can be changed within certain limits. In order to select another physical size you have to click on the appropriate one of the five radio buttons.