Physics 2F

Physics 2F

1. The planets in order are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto (dwarf planet)

2. The planets orbit the Sun as gravity pulls the planets towards the Sun

3. The force towards the centre of a circle is called the Centripetal force

4. A light year is the distance light would travel in year

5. Unmanned space probes are useful as they do not need food, oxygen or water

6. Key Processes

   • Uses of artificial satellites
     • Telecommunications (transmitting information between distant parts of the Earth)
     • Satellite navigation systems (‘satnav’)
     • Spying on other countries
     • Weather forecasts
   • A moving object will continue to move in a straight line at the same speed unless a force acts on it. For an object to move in a circle, a force has to act on it all the time. This force is called the centripetal force
   • Gravity is a force of attraction between masses. It provides the centripetal force needed to keep a satellite in orbit around a planet, or a planet in orbit around a star such as the Sun. Geostationary satellites are used for communications, and stay in a fixed position above the Earth’s surface. Low polar orbit satellites are closer to the ground, and are used for weather forecasting and imaging the Earth
   • Radio signals travel at the speed of light. This means that they take a long time to travel through the Solar System. For example, it takes just over one second for a signal to reach the Moon from the Earth, and up to 21 minutes to reach Mars
   • Unmanned spacecraft are cheaper than manned spacecraft, and safer, as they do not carry any astronauts. It is very difficult to repair an unmanned spacecraft in Earth’s orbit, and impossible once it leaves orbit. So the components are designed to be rugged and reliable
   • A light-year is the distance light travels in a year. Light travels very fast (300,000 km per second), and takes only about eight minutes to reach us from the Sun. It takes over four years to reach us from the next nearest star (Proxima Centauri), and 100,000 years to cross the Milky Way galaxy. We say that the distance to the next nearest star is four light-years, and the diameter of the Milky Way is 100,000 light years
   • Space probes are spacecraft that can visit other planets without the need for astronauts. They can send back information about things such as the:
     • Temperature, magnetic field strength and radiation levels
     • Gravitational field strength
     • The surroundings, including the composition of any atmosphere