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.
What else does gravity do?
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.
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. Image credit: NASA
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. That's what gives you weight. And if you were on a planet with less mass than Earth, you would weigh less than you do here.
Image credit: NASA
You exert the same gravitational force on Earth that it does on you. But because Earth is so much more massive than you, your force doesn’t really have an effect on our planet.
Gravity in our universe
Gravity is what holds the planets in orbit around the sun and what keeps the moon in orbit around Earth. The gravitational pull of the moon pulls the seas towards it, causing the ocean tides. Gravity creates stars and planets by pulling together the material from which they are made.
Gravity not only pulls on mass but also on light. Albert Einstein discovered this principle. If you shine a flashlight upwards, the light will grow imperceptibly redder as gravity pulls it. You can't see the change with your eyes, but scientists can measure it.
Black holes pack so much mass into such a small volume that their gravity is strong enough to keep anything, even light, from escaping.
Gravity on Earth
Gravity is very important to us. We could not 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 breathe. 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.
The GRACE mission helps scientists to create maps of gravity variations on Earth. Areas in blue have slightly weaker gravity and areas in red have slightly stronger gravity. Image credit: NASA/University of Texas Center for Space Research
GRACE detects tiny changes in gravity over time. These changes have revealed important details about our planet. For example, GRACE monitors changes in sea level and can detect changes in Earth’s crust brought on by earthquakes.
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Gravity is the force that pulls all elements of matter together. Matter refers to things you can physically touch. The more matter there is, the greater the amount of gravity or force. This means that the Earth or other planets have a great deal of pull and that everything on Earth is pulled back to Earth.
Gravity is the mutual attraction of two bodies in the universe. Since gravity refers to an invisible force pulling matter together, there are many examples of gravity. Every single thing has gravity, including people.
Some objects have much more gravity than others. The Earth, for example, has more gravity than people. This is why an object that falls is drawn to the Earth and returns to the Earth instead of being drawn to a person and flying at that person.
Some examples of the force of gravity include:
- The force that holds the gases in the sun.
- The force that causes a ball you throw in the air to come down again.
- The force that causes a car to coast downhill even when you aren't stepping on the gas.
- The force that causes a glass you drop to fall to the floor.
- The force that keeps the Earth and all of the planets in line in the proper position in their orbits around the sun.
- The force that propels a toddler down a slide.
- The force that causes the moon to revolve around the Earth.
- The force that keeps Jupiter's moons located around the planet.
- The force from the moon that causes the tides of the ocean.
- The force that causes your drink to rest at the bottom of your glass instead of hovering near the top of your glass.
- The force that causes an apple to fall downward from an apple tree.
- The force that keeps you walking on Earth instead of floating away into space.
- The force that causes a pen that rolls off of your desk to fall onto the floor.
- The force that causes a piece of paper that is blowing in the wind to eventually come back down to Earth.
- The force that causes a balloon that is out of helium to come back down to the ground.
- The force that causes a jump rope to come back to the ground after you swing it over your head.
- The force that causes a lock of your hair to fall to the floor after it has been cut off.
- The force that causes a rock to roll downhill.
Gravity has the same effect on every object. If you drop a huge elephant or if you drop a small, thin feather, they fall at the exact same speed. The feather will look like it falls more slowly and it does on Earth because there is air resistance that interferes with the force of gravity and can slow it down. However, if you dropped a feather and an elephant in a vacuum where there was no air resistance, they'd fall at the exact same speed because there is the exact same amount of force being exerted.
By reviewing examples of gravity, you can better understand gravity and how it works in a variety of situations in everyday life.
The term mass refers to the amount of matter in an object. For more science fun you can learn more about the mass of solar objects in Examples of Mass.