Gravity is one of the fundamental forces of nature. No one really understands exactly why, but gravity is a force that pulls objects toward each other. The mass of the objects and distance between the objects affects the strength of the force of gravity. Greater masses attract with more force and the force weakens as the objects get further apart.

Earth's gravity pulls objects toward the Earth's center. Barkley learned this the hard way when the balls he juggled kept falling to the ground. Earth's gravity pulls on the balls while the balls' gravity pull on each other. This caused Barkley to wonder why the balls didn't come together. Since the Earth is so much larger than the balls, the Earth's gravity pulls the balls straight down towards the Earth's center. The balls pull on the Earth with the same force that the Earth pulls on the balls. Since the Earth is so much bigger, then ball's force can't really affect the Earth as much as the Earth's force affects the much smaller balls.

The force of gravity works with an object's mass to determine the weight of that object. An object's mass is a measure of the material that makes up that object. Gravity's pull on an object is that object's weight. The Earth and the planets attract objects. Near the surface of the Earth, the main force affecting the weight of an object is the Earth because the object is closest to the Earth's center. Weight changes as the object travels away from the Earth and from planet to planet as the distance from the Earth and planets changes. The object's mass won't change.