1) The document explains that objects can orbit other large bodies like planets due to gravity. While gravity is pulling the objects towards the center, their horizontal movement is fast enough to constantly miss the surface in a curved path. 2) It uses the example of firing a cannon on a very tall mountain to show that with enough initial speed, the cannonball would orbit the Earth instead of hitting the ground. 3) Kepler's Third Law states that the square of an orbiting body's period is proportional to the cube of its average distance from the central body.