In this demo you will see the motion of a particular solution of the differential equation for the nonlinear pendulum
dy/dt = -0.2 y - sin(x)
On the left is the phase plane. On the right are the graphs of x(t) and y(t). The idea is to explain the motion that you are seeing. At various points the motion in the animation stops. At these points, you should quickly stop the video using the video controls at the bottom of the screen. The questions I ask at this point are: Where is the actual pendulum when animation stops? What is the direction of motion? Students should act out the motion using their arms as simulators of the pendulum. It is nice not to swing your arms so wildly so as to endanger the lives of your neighbors.
Click on this icon to download the animation).
Created 6/20/95, Robert L. Devaney