S-Cool Revision Summary

S-Cool Revision Summary

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

The four inner planets are called terrestrial planets and are small rocky planets: Mercury, Venus, Earth, Mars.

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: Jupiter, Saturn, Uranus, Neptune.

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.

Velocity is speed with direction.

If something is going in a circle, its velocity is changing, even if its speed is constant.

We call the force that keeps things moving in a circle a centripetal force. The centripetal force always acts towards the centre of the circle.

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.

  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 has seasons because it rotates on an axis, which is tilted.

The seasons change two significant things on the earth:

  1. The length of the day and night.

  2. The temperature and weather, due to the intensity of the sun.

The moon orbits the Earth every 28 days. As it goes around, it is caught in the shadow of the Earth, this is why we see different amount of the moon as the month goes by.

The moon and the Sun cause the sea to have tides. This is because of the gravitational attraction between the Sun, moon and water in the sea. The moon has the biggest effect, as it is closer to the Earth.

Our solar system is a collection of planets orbiting a star. Our Sun is gravitationally bound to a huge collection of other stars. This collection of stars is called a galaxy. Our galaxy is called the Milky Way. There are lots of galaxies in the Universe.

The Big Bang theory:

There is evidence that the Universe is expanding.

This evidence is found when we look at the electromagnetic radiation emitted from other galaxies.

The Doppler Effect makes waves appear to have a longer wavelength if their source is moving away from you. It also means the wavelength will appear shorter if something is moving towards you.

3 main possibilities of how the world might end...

  1. If there is too much matter in the Universe, the gravitational attraction between all the masses will eventually pull all the galaxies back together into a big crunch. - Closed universe.

  2. If there is not enough matter in the Universe, everything will keep moving apart forever. - Open universe.

  3. If there is just the right amount of matter in the Universe, the expansion of the Universe will slow down until it is expanding so slowly that it will appear the Universe has stopped expanding. - Flat universe.

Stars start off in the same way, but their end depends on how much mass they have.

Nuclear fusion: Gravitational attraction pulls hydrogen atoms together. The initial star will be big and cold. As it pulls its mass closer together, the hydrogen atoms will start to fuse together to make helium atoms. A huge amount of energy is released.

The following diagram shows the life of a star:

Life of Stars