This HTML 5 app demonstrates the variation of elongation, velocity, tangential acceleration, force and energy during the oscillation of a 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 length of the pendulum, the gravitational acceleration, the mass 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.
The dependence of the oscillation period upon the amplitude was neglected in the calculations.
Thanks to Mr. Marc Burgess for his valuable suggestions!