# What is Gravity?

November 26, 2012

Hi, I’m  Emerald Robinson, and in this “What Is” video we’re going to discuss one of the biggest forces of nature: gravity.

Most of us define gravity as the force that holds us down on the earth, or causes things to fall. But it’s a little more complicated. A better definition of gravity is “the attraction between two masses.”

Every object in the universe, from the smallest atom to the largest galaxy, is made of matter. The amount of matter in something makes up its “mass.” Things that have a lot of matter in them have a high mass – and a high gravitational force, or “pull.”  More mass in an object means it has a greater attraction to other objects.

The gravitational force between two objects also depends on how far apart they are. The closer two objects are together, the stronger the gravitational force is between them.

How do these things affect us? You and the earth both have mass. Therefore, you pull on the earth, and the earth pulls on you. However, the earth’s mass is much, much larger than yours, so its gravitational force is enough to keep you down on its surface. When you jump, you push away from the earth.  But, because the earth’s mass is so much bigger, its gravitational force pulls you back down.

Astronauts on the moon experienced about one sixth the gravity that they felt on earth. This is because the moon has a smaller mass than the earth. Gravity is also why we weigh less on the moon, since weight (in pounds or kilograms) depends on the force of gravity on an object.

Gravity even holds the earth’s atmosphere in place, causes the ocean’s tides, and keeps the moon and planets in their orbits. It’s truly an important force.