Gravity
noun

1. The force that pulls anything with mass towards the center of the earth.

What is Gravity?

Gravity is a very important force. Every planet in the galaxy experiences a gravitational pull. It is the force that keeps planets from floating off into space. It also keeps planets in orbit. You can think of it as the glue that holds the planets together in orbit. 

Gravity also stops things on planets from flying away. Anything on a planet with mass is pulled towards the center of the planet because the gravity is coming from the center. But on different planets the gravity is different. Some planets may have a strong gravitational pull while others may have little or no gravity on them. For example the moons gravity is less than 1/6 of the earth's. Also things with smaller mass are attracted to things with larger mass such as we are pulled to the center of the earth, the moon is pulled towards the earth and the earth is pulled towards the sun.