Gravity and Orbits


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.
  1. What happens when you (slightly) decrease earth's forward velocity? What happens if you (slightly) increase it?
  2. Does this simulation agree with Kepler's 2nd law?
  3. 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?
  4. Using the "To Scale" mode, is it easy or difficult to make the earth crash into the sun? Why do think that is?
Credits: PhET Interactive Simulations University of Colorado Boulder