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What goes up, must come down

What is gravity? We feel it every single day, although we can’t see it, we know its there. The planets, moons and sun all have their own a gravitational field.

Gravity fields affect anything with energy. People, houses, mountains even our moon feels the full of the earths gravitational field.

If you jump on the Earth, Earth’s gravity pulls you back down. If your on the Moon, the moons gravity would pull you back down. However you can jump higher on the moon, because there is less gravity.

Gravity is the force that attracts objects to each other. The Sun’s gravitational pull keeps all the planets aligned.

Our earth’s keeps up on the ground, the moon orbiting and holds an atmosphere of gases.

This is why planets with weak gravitational pull, (mercury and mars) have extremely thin atmospheres.

If you wanted to leave earth and go into space, you would first have to overcome earths gravity. To sufficiently overcome earths gravity you would need an escape velocity of 40,000 km/h.

The force amount of gravity produced isn’t the same for every object. The greater the mass the stronger its gravitational pull is.

For example if you weighed 100kg on Earth, than you would weight 38kg on mercury and 254kg on Jupiter.

We measure gravity in Newtons.  

Gravity doesn’t treat all objects equal either. The greater the mass of an object, the more gravity is pulling on it.

This is tricky when building something that needs to fly.

The more fuel you add in, the more weight you have, meaning you need more power.

So if gravity pulls everything down, why is it that some things float in water and don’t sink?


Archimedes' define buoyant force as:

The buoyant force or up thrust experienced by and object immersed in a liquid equal to the weight of a the liquid displaced.

Click here for more info above buoyancy

So, if gravity pulls things in, why don’t all the planets simply gravity into the sun?

Image if you standing with a tennis ball. Now if you just throw the ball a little bit, earths gravity will pull it down and make it crash to the ground. But if we throw the ball hard and fast enough, the ball will follow the curvature of the earth.

Since the Earth is round, the ball you threw would ‘fall’ all the way around the planet.  If it goes fast enough it will keep going around and around, the ball would stay in orbit.

On the animation to the left click 1# for a slow ball and 2# for a fast ball.

Issac newton was one of the greatest scientists and mathematicians who ever lived.

Born in 1643 he he was fascinated by maths, physics and astronomy. He went on to complete a bachelors and masters degree.

He is mostly know for his 3 laws.

Click here to learn more about his laws of physics.

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