Gravity and Motion

The law of gravity states that every object in the universe attracts every other object. The strength of gravity increases as mass increases. The strength of gravity decreases as distance increases. Both the Earth and Moon exert gravitational pulls on each other.

The Earth has a greater gravitational pull on objects because it has a larger mass than the Moon. Earth's gravitational pull is about six times greater than the Moon's gravitational pull. On the Moon, you would weigh about one-sixth of your weight on Earth.

Inertia is the tendency of an object to resist change once it is in motion. An object will stay in motion at a constant speed and direction, unless it is acted on by another force. The Moon and the Earth are in constant motion as they rotate on their axes, and therefore they have inertia.

The combination of gravity and inertia keeps the Moon moving in orbit around the Earth. If there were no gravitational pull on the Moon, it would move in a straight line away from the Earth into space. If the Moon did not have inertia, then it would be pulled by Earth's gravity and crash into Earth. The same forces keep the Earth in orbit around the Sun.