# Phun with Gravity

Now that you have observed the bowling ball being hit in three directions and have described it's motion let's perform some more tests.

Part 1: How would you have to hit the ball to keep it going in a circle? Try it out!

Part 2: Now that you have figured that out, let's examine planetary motion. The planets going around the sun follow almost circular orbits (they are in fact elliptical orbits). How does the above experiment illustrate the direction of the force that the planets experience from the sun? What does this tell you about the force that holds the solar system together?

Part 3: What is the force that holds the solar system together called? Let's work on some more on this force. Drop an object. Which way does it fall? Suppose we opened a window and dropped objects which way would they go? Suppose we dug a deep hole in the ground and dropped the objects into the hole which way would the objects go? Suppose we dug a tunnel to the center of the earth, where would the object go? Now suppose we continued this tunnel all the way through the earth to the other side. Now describe the motion of the object that is dropped in the hole. The correct answer may surprise you!