Assumptions - Simple Harmonic Motion (Pendulum)
The applet simulates both simple pendulum motion and uniform circular motion. At the small amplitudes used in the applet, the pendulum's motion is very nearly simple harmonic motion and visually indistinguishable from projected uniform circular motion.

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 simple harmonic motion, but for sufficiently small amplitudes, the motion simulated by the applet is an excellent approximation to the true motion.

The following additional assumptions are made in creating the simulation.