This simulation shows the orbit of the earth and moon about the sun. The position and velocity of each object can be adjusted using the mouse.

[list=1][*]What happens when you (slightly) decrease earth's forward velocity? What happens if you (slightly) increase it?[/*][*]Does this simulation agree with Kepler's 2nd law?[/*][*]If you decrease the sun's mass a little bit, the earth will stay in orbit. If you decrease the sun's mass to 1/2 it's current value, the earth escapes. Why is 1/2 a special value?[/*][*]Using the "To Scale" mode, is it easy or difficult to make the earth crash into the sun? Why do think that is?[/*][/list]Credits:[br]PhET Interactive Simulations[br]University of Colorado Boulder[br]https://phet.colorado.edu