# What is gravity?

Gravity is a concept that comes up throughout secondary science teaching - but what is it? Watch this short video to find out.

As the old saying goes, what goes up must come down. But why does that happen? And does that always happen? Our understanding of what gravity is has changed from being a mysterious force that no one could explain, to the mind-blowing realisation by Einstein that gravity is the curvature of spacetime caused by massive objects.

## How can you explain gravity?

A great way of explaining a tricky topic like gravity is to split your explanation into three levels – beginner, intermediate and advanced – and use the explanation most appropriate for your students.

Here, we’ve split the answer to the question “What is gravity?”, beginning with the basics of gravity and ending with the more advanced, and currently accepted, the idea of what gravity is.

What is gravity? – Basic

Imagine you are holding a ball in your hand – what happens when you let go of the ball? It falls to the ground because the Earth’s gravity attracts the ball to the Earth. Gravity is a force that attracts objects towards each other, so not only is the Earth attracting the ball, the ball is attracting the Earth too.

### What is gravity? – Intermediate

Every object that has mass creates a gravitational field that surrounds it and attracts other objects. The Earth has a gravitational field and any object inside the Earth’s gravitational field will experience an attractive force towards the Earth.

If I have a ball in my hand and let go of the ball, even though the ball has a gravitational field of its own, it will be attracted towards the Earth because the Earth’s gravitational field is stronger.

### What is gravity? – Advanced

Our current understanding of what gravity is comes from the brilliant mind of Albert Einstein. Imagine four people holding a sheet of cloth tautly, with each person holding a different corner of that cloth. That cloth represents space and time. If we place a ball on the sheet near its centre, what would happen? The ball would cause the cloth to sag, in other words, the ball would distort or bend the sheet of cloth.

What happens if we roll another ball along with that sheet? That ball will follow the curvature of the cloth and will appear to accelerate towards, or be attracted to, the ball lying at the centre of the cloth.
Einstein realised that objects with mass bend space and time, the fabric of our Universe, and that gravity is the curvature (or bending) of spacetime caused by those objects.
If you’d like to learn more about teaching physics, astronomy and space to secondary students, check out the Royal Observatory Greenwich online course, below.