This applet illustrates "Newton's Cannon" where orbits can be thought of as taking ballistic motion to large initial velocities in order to achieve orbits.  This applet allows the user to experiment with different firing velocities.  The initial velocity is set with the slider at the bottom right hand side of the applet window.  The cannon is fired by clicking on the play button.  In order to "reload" the cannon, the user must click on the reset button.  In addition to the play, reset and pause buttons, there is a "cheat" button which will select the correct speed for circular orbits. 

Things to consider:

• What happens when the cannon ball is given more than the speed required for circular orbits?
• What would happen to the trajectory of the cannon ball if the solid earth's surface did not stop the projectile?  Pretend that all the earth's mass is concentrated at its exact center.
• What would happen if the earth had more mass (and hence produced stronger gravitational attraction)?  What if it had less mass?