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.

Note that the applet only exhibit's the planet's acceleration. The gravitational force exerted by the sun on the planet is in the same direction as this acceleration and has a magnitude equal to ma where m is the planet's mass and a the magnitude of the planet's acceleration.

"Activities" under Related Items suggests investigations to be carried out with the applet on the gravitational force exerted by the sun on the planet.