Let's pretend that gravity stopped. It is only make-believe, but it shows what gravity does for us. Gravity is the invisible pull that makes things fall down and keeps you on the ground. If it stopped, nothing would hold you down. When you throw something up, gravity pulls it back down. With no gravity, nothing would pull a thrown ball back.

Gravity holds down the air we breathe, so Earth keeps its blanket of air. Without gravity holding it, Earth would not keep that blanket. The Moon's gravity pulls on the seas, and that makes the ocean tides go up and down. Without that pull, there would be no such tides.

Your mass is the amount of stuff you are made of. Everything that has mass has gravity, and things with more mass pull harder. Gravity also gets weaker the farther apart two things are.

Your weight is how hard gravity pulls on you. The pull comes from all of Earth's mass. On the Moon you would weigh about one-sixth of what you weigh on Earth, because the Moon pulls less. Your mass stays the same even when your weight changes. With no gravity, there would be no pull, so you would have no weight.

The Sun is a giant ball of hydrogen gas, and gravity holds all of that gas together. It would take almost 1,000 Jupiters to fill up the Sun. With no gravity, nothing would hold the Sun's gas together.

Gravity keeps the Moon going around Earth, and Earth going around the Sun. The Sun's gravity also keeps Earth at a comfortable distance for its light and warmth. Without gravity, nothing would keep the Moon or Earth going around.

Everything in orbit is falling around its planet. It moves sideways so fast that it keeps missing the ground. The International Space Station is in low Earth orbit. It circles the planet once in about 90 minutes.

You may have heard that astronauts float because there is no gravity in space. In fact, gravity does not stop in space. Astronauts float because they are in free fall. Everything inside the station is falling together. A roller coaster can feel a bit like that. At the top of a drop, free fall gives you a brief feeling of weightlessness.

Words to know

• gravity: invisible pull
• mass: amount of stuff
• orbit: path around something
• hydrogen: a light gas
• weightlessness: floating feeling

The short version

If gravity stopped, nothing would pull things down or hold you to the ground. That is only make-believe, but it shows what gravity does. Gravity is the invisible pull that makes things fall down. It holds down the air we breathe, and the Moon's gravity pulls on the seas to make tides.

Quick facts

• Gravity is the invisible pull that makes things fall down and keeps you on the ground.
• Gravity holds down the air we breathe, so Earth keeps its blanket of air.
• On the Moon you would weigh about one-sixth of what you weigh on Earth, because the Moon pulls less.
• Gravity does not stop in space; astronauts float because they are in free fall.
• The International Space Station circles Earth once in about 90 minutes.