Is gravity the same everywhere?

"Is Gravity measured to be the same strength and force no matter where it is in the Universe, or does it change when nearer large planets/objects and the spaces in between?"

Question posed by Margaret in response to Where do moons come from?

Gravity is a force, and forces try to move things either towards something or away from something. Gravity is an attractive force- it pulls things together. It is produced by anything with mass: anything that is made of 'normal' matter, that you could imagine holding or touching: the Earth has a gravitational field, and so does the Moon. But so do your coffee cup, mobile phone and even yourself.

If you've ever held two magnets so that two different poles are close but not touching, you will know that you can feel the two magnets pulling towards each other. You can't see or feel this force directly, but you can feel the effect it has on the two objects. Gravity works in a similar way, but is much, much weaker. It takes something the size of a planet, with all of the particles in that planet, pulling together to produce a noticeably similar effect.

Back to the magnets: if you hold the magnets close together, you can feel them tugging quite strongly. As you move them apart, the attraction rapidly becomes less strong. Gravity is pretty similar: the further away you go from something that's producing gravity, the less you feel its effect.

So...

Is gravity the same everywhere?

No. The effect you feel is affected by two things:

• Mass

Mass is the amount of stuff that goes into making something. Things with more mass produce more gravity, so the force of gravity that you feel is stronger when you're close to more massive* things.

• Distance

If you're closer to a massive object, you feel the effect of its gravity more strongly than someone else who is further away.

For anyone who likes numbers, the strength of gravity decreases with the square of the distance. That means that if you move twice as far away, the effect of gravity that you feel is 4 times smaller. If you move 5 times further away, the effect you feel is 25 times smaller, and so on...

* 'Massive' means 'has lots of mass' rather than 'is really big'.