## Want to keep learning?

This content is taken from the National STEM Learning Centre's online course, Teaching Primary Science: Physics. Join the course to learn more.
2.7

# What is gravity?

Gravity is a non-contact force that was observed famously by Sir Isaac Newton, who watched an apple falling from a tree to the ground. It is a pulling force exerted by the Earth which draws objects towards its centre.

Gravity is dependent on the mass of something. Any object which has mass has a gravitational pull and attracts other objects towards it. The gravitational force of the Earth pulls objects towards it. The greater the mass of an object the stronger its gravitational force or pull. Newton was the first to realise that gravity existed in space and it was the force which holds the Moon in orbit around the Earth and planets in orbit around the Sun.

## The difference between mass and weight

Mass is the amount of matter that an object is made from and is measured grams and kilograms. This is confusing as in everyday language we often weigh things out, rather than find the mass of something. Weight is a downward force due to the pull of gravity and is measured in Newtons, after Sir Isaac Newton.

## Gravity in Space

On Earth the pull of gravity is greater than on the Moon. Your mass would be the same on both the Earth and the Moon, but your weight would be one sixth less on the Moon than on Earth. This is because gravity on the Moon is one sixth of that on the Earth. Astronauts on the International Space Station (ISS) experience weightlessness, they appear to be floating around the ISS. This can lead to the misconception that there is no gravity in space. The ISS orbiting the Earth is still affected by the Earth’s gravity. It is in fact falling around the Earth very quickly. If it slowed down then the Earth’s gravity would cause it to be pulled back down to Earth. This is a tricky idea to get across to children. Sometimes we can experience a moment of weightlessness on Earth. This could be when in a lift or at the top of a roller coaster just as it starts to go down from a height.

## Suggest

Can you think of ONE other example that you could discuss with children to help them to understand this idea?