Stepwising

Stepwising invites you to explore, play with, and learn about gravity. You can check out Kepler's laws of planetary motion, observe and discover solutions to the 3-body problem, or try to drive a frictionless car around a circular track of ice.
The program closely approximates the motion of stars, planets, moons, and other celestial objects moving through space under the influence of their gravitational fields. It does this recursively: an object's position determines the amount of force on it, the amount of force on it determines its acceleration, its acceleration determines its average velocity over a short period of time, and its average velocity determines its next position. If the time interval between calculations is small, a very good approximation of the motion is produced.