Orbit

Key Stage 2

Meaning

An Orbit is the path planet takes around a star and the path a moon takes around a planet.

A Planet orbiting a Star.

About Orbits

An orbit is a roughly circular path, but can be stretched out into an oval shape.

The Moon orbits the Earth. This means The Moon takes a circular path around the Earth.

All the planets orbit The Sun. This means the planets take a circular path around The Sun.

Key Stage 3

Meaning

An Orbit is the path an asteroid, comet, planet or dwarf planet takes around a star and the path a moon takes around a planet.

About Orbits

Moons orbit planets and planets orbit the stars due to gravity.

Newton was the first person to realise that objects were held in orbit by gravity which he explained in his Law of Universal Gravitation.

Gravity is a constant force directed to the centre of a massive object.

The Moon feels a force pulling it towards the centre of the Earth. The Earth feels a force equal in magnitude but opposite in direction to that of The Moon.

The planets are pulled towards The Sun by gravity.

Key Stage 4

Meaning

An orbit is the circular or elliptical path that an object takes a more massive object due to a force of attraction acting between them.

About Orbits

Orbits are caused by a force of attraction between two objects acting towards their centres.

Planets orbit Stars due to the force of gravity.

Higher

There are two types of orbit you should know:

• Circular orbit - An orbit where the distance between the two objects (the radius) remains constant. In this orbit the speed of the orbitting object is constant. However, the velocity of the orbitting object is constantly changing due to the changing direction.

This animation shows acceleration due to the changing direction of a circular orbit of the blue object around the red object. A circular orbit is one of constant radius.

• Elliptical orbit - An orbit where the distance between the two objects changes. In this orbit the speed of the orbitting object changes with the distance between the objects. The greater the distance the smaller the speed.

This animation shows the elliptical orbit of a planet around a Star. As the planet gets further from the Star the speed of the planet decreases. As the planet gets closer to the Star the speed of the planet increases.

References

AQA

Orbit, pages 276, 278-9, GCSE Physics; Student Book, Collins, AQA

Orbits, page 101, GCSE Physics; The Revision Guide, CGP, AQA

Orbits, pages 236-237, GCSE Physics; Third Edition, Oxford University Press, AQA

Orbits, pages 249-50, GCSE Physics, Hodder, AQA

Orbits, pages 320, 321, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA

Orbits; circular, pages 253-5, GCSE Physics, Hodder, AQA

Orbits; speed of, pages 254-5, GCSE Physics, Hodder, AQA

Edexcel

Orbits, page 59, GCSE Physics; The Revision Guide, CGP, Edexcel

Orbits, pages 118, 120-121, GCSE Physics, Pearson Edexcel

Orbits, pages 184-186, GCSE Physics, CGP, Edexcel