Gravity

Gravity
By Sam Irani

       Why do you land on the ground when you jump up instead of floating off into space? Why do things fall down when you throw them or drop them? The answer is gravity: an invisible force that pulls objects toward each other. Earth's gravity is what keeps you on the ground and what makes things fall. Gravity is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun.
An animation of gravity at work. Albert Einstein described gravity as a curve in space that wraps around an object—such as a star or a planet. If another object is nearby, it is pulled into the curve.
         Anything that has mass also has gravity. Objects with more mass have more gravity. Gravity also gets weaker with distance, so the closer objects are to each other, the stronger their gravitational pull is. Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body which gives you weight. And if you were on a planet with less mass than Earth, you would weigh less than you do here.
Infographic showing how much you'd weigh on other planets and the moon
Gravity is very important to us, and we couldn't live on Earth without it. The sun's gravity keeps Earth in orbit around it, keeping us at a comfortable distance to enjoy the sun's light and warmth. It holds down our atmosphere and the air we need to breath. Gravity is what holds our world together. However, gravity isn’t the same everywhere on Earth. Gravity is slightly stronger over places with more mass underground than over places with less mass. NASA uses two spacecraft to measure these variations in Earth’s gravity. These spacecraft are part of the Gravity Recovery and Climate Experiment (GRACE) mission.
A gravity map of Earth made with data from the GRACE mission
In the future we may have certain abilities to control or live in an anti-gravity environment which might come sooner than later. Up until now, the prospect of anti-gravity technology has been strictly confined to science fiction stories and films alike. However, physicists are set to begin an experiment that may well revolutionize our understanding of how the universe works. They will be investigating the idea that antimatter may generate a gravitational field that repels that produced by ordinary matter.

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