IGCSE Online Tutorial - Jesmul Sir's Portal
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IGCSE Online Tutorial - Jesmul Sir's Portal

Physics GCSE: Space

The Solar System

The Planets
The Solar System is made up of the nine planets, including the Earth, that orbit (go round) the Sun.

See whether you can name them on the diagram below:
The four inner planets are called terrestrial planets and are small rocky planets.
Between Mars and Jupiter, there is an asteroid belt, which may be the remains of a planet.

The next four are called gas giants and are large planets made up of gas.
Pluto is a very cold lump of rock, with a moon - Charon - nearly as large as Pluto.

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Decide whether the following facts are true or false:
The moon orbits the earth in 28 days and the Earth orbits the sun in 365¼ days. Each planet takes a different amount of time to orbit the sun.

Orbits and circular motion

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If something is going in a circle, its velocity is changing, even if its speed is constant. This is because it is changing direction. If the velocity is changing the object must be accelerating. We know from Newton's Laws that something will only accelerate when a force is being applied.

We call the force that keeps things moving in a circle a centripetal force. A centripetal force can be provided in a number of ways. See whether you can identify which of the forces below provides the force in each situation:
Notice that the centripetal force always acts towards the centre of the circle.

Help the hammer thrower below release the hammer at the right time. Remember, as soon as the centripetal force is removed the object will travel in a straight line.
Satellites

Satellites are also held in orbits around the Earth by the gravitational attraction of the Earth. There are two main types of satellites:

1. Geo-stationary orbit satellites:
The satellite rotates around the Earth once every 24 hours, so it is able to stay over one point on the Earth. This is useful for communications, as microwaves can be directed at the satellite, which then sends them back to a different point on the Earth. The satellite is always in the same position relative to the Earth.

2. Polar orbit satellites:
The satellite can orbit the Earth many times in a day and see the whole Earth as it travels. The Earth is rotating as the satellite orbits, so the satellite sees a different part of the Earth each time it goes around. These satellites are used for weather forecasting and for spying.
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