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Gravitational forces

Tutor: Katherine

# ​​Gravitational forces

## In a nutshell

Anything with mass has a gravitational force on other objects with mass. The larger the object, the bigger the force of gravity. The Earth has a bigger gravitational pull than the Moon, and the Sun has a bigger gravitational pull than the Earth.

### Definitions

#### Definition

Force

A push or a pull

Gravity

An attractive force between objects with mass

Orbit

The curved path which objects move around larger celestial objects in space

## The force of gravity

Gravity is an attractive force between objects with mass. You are attracting the Earth towards you, and the Earth is attracting you to it (which is why you don't float off into space!)

The bigger the mass of an object, the stronger the gravitational force. Gravity causes the Moon to orbit around the Earth, and the Earth to orbit around the Sun.

Saturn is much bigger than Mercury. Therefore, the gravitational pull on Saturn, is much larger!

The further apart objects are, the weaker the gravitational force.

The planet Venus has a similar mass to Earth's. However, because Venus is closer to the Sun, there is a larger gravitational force between the Sun and Venus.

## The gravitational force between the Earth and Moon

The Moon orbits the Earth due to the gravitational forces between the Earth and the Moon. As the Earth is much bigger than the Moon, it has a larger gravitational pull. However, the Moon also pulls on the Earth, which is why they don't crash into each other!

Due to the forces between the Earth and the Moon, the Moon is tidally locked. This means that only one side of the Moon is visible to Earth. This causes the Moon to appear to change shape, depending on where the Moon is around its orbit of Earth. We can only observe the side that is lit up by the sun.

When only the side which is in shadow faces the Earth, this is called a New Moon. When the lit up side is in full view, this is called a Full Moon. In between there are quarter moons, crescents and gibbous moons.

##### 1. Waning Crescent 2. New Moon 3. Waxing Crescent 4. First Quarter 5. Waxing Gibbous 6. Full Moon 7. Waning Gibbous 8. Last Quarter

You can see other effects the Moon's gravity has on the Earth just by going to the beach. The Moon causes the rise and fall of the sea (the tide).

## The gravitational force between the Earth and the Sun

 The Sun is about $333,000 \times$​ heavier than the Earth, so has a much larger gravitational force. Although the Sun appears to move in the sky, it is the Earth that orbits around the Sun. It takes one year for the Earth to complete an orbit.

## FAQs - Frequently Asked Questions

### What is gravity?

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