Newton's Planet Simulator
Let the planets orbit around the sun. After watching them for a while, use arrow keys to move the sun. Check out why the planets more so differently. How is the gravity programmed or each one?
If you think it's a mess, the space bar will clear the lines away. Insert the "hide" block ('looks" commands) into one or two of the planet scripts. If you like a planet's motion, duplicate and change the value of its "G-mass" variable to make it heavier or lighter.
Isaac Newton was the first person who figured out the mathematical requirements to have stable orbits. You are darn lucky the planets actually behave like Newton told them, not like the light blue one!
Inspired by Isaac Newton and Jacob Barnett.
The images (background and space shuttle) are taken from the NASA web site.