# Gravity

#### Back to Different Types of Forces

This is a simple tutorial describing the principles of gravity, aimed at Grade 9/10 students (GCSE).

## What is gravity?

There are forces between objects that attract them to each other. These forces are referred to as gravitational forces. You'll likely have heard of gravitational forces before, in the form of gravity - it's what keeps the planets orbiting around the sun, and us from floating around in the sky.

## Why don't all objects experience a gravitational pull to each other?

Well they do; gravitational forces are not limited to large objects. In fact, every single object experiences a gravitational pull to the objects around it - even to you. You're probably wondering then why we don't see objects randomly moving around to get closer to each other. This is because the magnitude (size) of the attractive gravitational force between objects depends on a couple of factors:

• the masses of the objects involved, and
• the distance between their centers.

We can describe this relationship using the below formula, where m1=mass of the first object, m2=mass of the second object, r=the distance between their two centers, and G=the gravitational constant.

## What does this formula tell us?

It tells us two things:

• It tells us that the larger the objects are, the greater the pull will be.
• If you double the mass of an object, you will double the strength of the force pulling them towards each other.
• It also tells us that the closer the objects are to each other, the stronger the pull will be.
• If you halve the distance between objects' centres, you will increase the strength of the force four-fold (because 2 squared = 4).

## Wait, so why don't everyday objects get pulled to each other?

Everyday objects do experience a gravitational pull towards each other, but the pull is so small that it is well outweighed by other forces, including:

If these forces were removed, then objects would move closer to each other - but alas, we're likely never to see that happen.