The applet on Page 2 simulates the motion of a planet around the sun (or another fixed star), or the motion of a moon or satellite around a planet.

For detailed information on how to use the applet, go to Applet Help on the applet's Help menu and look at Help and ShowMe. A Lesson accompanying the applet is available there as well.

The applet is available in two versions: "Planet Motion 1" and "Planet Motion 2". The applet on Page 2, "Planet Motion 1", allows you to vary the shape of the planet's orbit by varying the eccentricity and semi-major axis of the orbit. In "Planet Motion 2", you can vary the shape of the orbit by varying the energy and angular momentum of the planet-sun system. "Planet Motion 2" is found at Energy/Energy Conservation/Simulate It/Planet Motion/Planet Motion 2.

When the eccentricity and semi-major axis of a planet's orbit are set, the values of the energy and angular momentum are uniquely determined, and vice versa. In either applet, if the values for one pair of values are set by the user, the values for the other pair are calculated and displayed in that applet's data box.