The simple pendulum motion simulated by the applet is such that the vertical projection of this motion onto a horizontal axis is exactly simple harmonic motion. The true motion of a simple pendulum is not not quite like this, but for sufficiently small amplitudes, the motion simulated by the applet is an excellent approximation (SHM approximation) to the true motion.

The following additional assumptions are made in creating the simulation.

• The pendulum string is massless.
• The pendulum bob behaves like a mass point.
• The system is frictionless.
• The potential energy of the pendulum is taken to be zero when the pendulum is at its equilibrium point, which is at the bottom of the pendulum's swing.