Planets and moons are shaped like a ball. But how comes people, animals and generally all things stick to the surface without falling off?

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The force that keeps everything from flying away into space is called Gravity. If you pick up any (non-fragile) object around you up and let go of it you can see it in action!

If you throw an object Gravity will pull it toward the ground. Less Gravity means you can throw higher and farther . With very high Gravity you might not even be able to raise your arm to throw.

Gravity not only makes sure we don’t become involuntary astronauts (which would be quite dangerous without a proper space suit) but also keeps moons and satellites and space stations orbiting around planets. If Earth’s Gravity would be less our moon would just float away into the depths of space.

Our Moon’s Gravity is roughly only 70% as strong as what we experience on earth. That’s why astronauts can make large jumps on its surface which would be impossible down here since the suit they are wearing is indeed quite heavy and cumbersome.

On earth Gravity is 1g (so the Moon sits at 0.7g). The height that you can jump is limited by this force and anything you throw gets pulled back to the ground. The heavier the objects is, the faster it will be pulled down until it reaches a solid surface.

To escape Gravity you need to use a powerful engine like a rocket ship. And you need a lot of force since where the International Space Station flies in orbit (about 354km up) Gravity is still about 90% as strong as on the surface.

If the Gravity becomes higher than what we are used on Earth it eventually becomes impossible to jump or even move around. Your limbs and body would feel much heavier (and you would get tired much faster) and the force will begin to compress you, reducing your height (for example floating in space you would be a few centimeters taller than now). If it would be really strong everything would be looking like a pancake – although not as tasty, because getting turned into a pancake is a very unpleasant and often quite deadly process.

If Gravity would be close to 0g everything would be incredibly light. You could jump higher than a skyscraper (be careful not to go too high or you might never come down). Your arms would probably float next to your body and you would be bouncing around like a pink rubber penguin. If you throw stuff around it would almost fly in a straight line and possibly orbit the planet or go on a trip to space.

So we can be really thankful that Earth’s Gravity is 1g. Because of that we don’t have to be afraid of flying of our home planet when we are a bit distracted. Imagine having to use a rope all the time to tether you to the ground! But luckily all living things have adapted to be able to live in these conditions.

Everything on planet Earth is influenced by Gravity and would look very different if it would have developed on another planet. Our human skeleton for example is perfectly suited for walking around on earth. We would be much shorter and possibly have heavier, thicker bones if our home planet would have a higher gravity. Imagine having to lift your foot when it feels that it weighs twice as much!

If walking was very difficult, there probably wouldn’t be as many organisms with legs and nothing could fly. They might use gases that are lighter than air (like helium) to help them move around. Can you imagine an animal that lives on a planet with extremely low Gravity?

Below you see an alien from a planet that has extremely strong gravity