1. Gravity

2. What is gravity?
We don’t really know. Some scientists say that it is a particle called a graviton that travels at the speed of light. Einstein says that gravity distorts the fabric of space and time.

4. We can define it by what it does: It attracts objects to each other.
What is Gravity?
We can define it by what it does: It attracts objects to each other.
Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. It is an attraction that exists between all objects, everywhere in the universe.

5. The amount of force gravity has depends on two things: Mass and Distance

6. So what is mass?
The amount of matter – or – stuff something is made of. Mass does not change anywhere in the universe. If something has a mass of 10 kg on Earth it has a mass of 10 kg everywhere.

7. What you need to know about gravity:
Gravity depends on two things: Mass and distance
The higher the mass the higher the gravity.
The shorter the distance, the higher the gravity.
Gravity pulls objects to the center of the mass.
Think magnet!

8. Earth’s Gravity
Earth's gravity is what keeps you on the ground and what causes objects to fall.
Gravity is what holds the planets in orbit around the Sun
The sun is so very massive and has so much gravity that it keeps the planets orbiting around it

9. Gravity and Weight Gravity is what gives you weight
Gravity and Weight Gravity is what gives you weight. It pulls on all of the mass in your body to the center of the Earth and that is how we measure weight.
Weight is measured in a unit called newtons. A newton is 1 N = 1 kg m s2

10. Weight on Other Planets
Although the size of the astronaut below doesn’t change, the smaller the planet or moon, the less gravity there is to pull him toward the center, so he weighs less

11. Gravity is extremely powerful
Especially if the mass is very large and the distances very small. Io is the closest moon to Jupiter. It is incredibly hot, and is covered with volcanoes. It is hot because the gravity pull on the near side of Io is higher than the gravity pull on the far side of Io. As it rotates the planet is flexed. The friction from this flexing causes enough heat to melt rock.

13. So why don’t we all fall into the Sun?
Because all of the planets and bodies in the solar system are moving very fast. Gravity pulls at them, but if they move fast enough they don’t get pulled in. Think about a ball on a string. As you swing it around, the string pulls on it. If you were to let go, the ball would travel in a straight line. The planets are travelling in a curve because gravity is pulling on them.

14. Ok, so why doesn’t the Moon orbit the Sun?
I thought maybe because it is so close to Earth that itcanceled out the HUGE mass of the Sun. But That’s not why. And I can’t tell you why because I can’t figure it out. So if any of you become astro physicists, call me and explain it to me.

15. Putting it All Together
Using your newfound knowledge about gravity, explain what is happening in this picture.

16. For more resources created by Vanessa Moran, please visit her store at
Gravity Credits
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Graphics from the Pond at
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For more resources created by Vanessa Moran, please visit her store at
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