P5a - Satellites, Gravity and Circular motion

P5a - Satellites, Gravity and Circular motion

1. satellites

   • an objects that orbits a larger object in space
   • natural, e.g. the Moon orbits Earth
   • artificial, e.g. have been put in space by humans
   • kept in orbit by gravitational force
   • Gravity: universal force of attraction between masses - keeps planets orbiting the Sun and satellites orbiting the Earth

2. centripetal force

   • the force that acts towards the centre of a circle that keeps an object moving in a circle
   • gravity provides the centripetal force to keep a satellite in orbit
   • gravitational force between 2 objects gets weaker as they get further apart.
   • planets further away from the sun experience a lower gravitational force and have a longer orbital period.

3. different orbits

   • low polar orbit satellites
     • used to look at Earth's surface
     • have to be low enough and orbit over the poles so they can see Earth segment by segment
     • each orbit = about 100 minutes
     • uses: imaging Earth's surface; weather forecasting; military uses - spying
   • geostationary satellites
     • each orbit = 24 hours
     • remain in a fixed position above Earth at all times
     • orbit much higher above Earth
     • uses: communications; satellite TV; weather forecasting
   • artificial satellites
     • can orbit at different heights above Earth's surface
     • orbital period is longer if the satellite is at a higher position above Earth
   • comets
     • orbit the sun in an elliptical loop
     • when close to the sun, it has to travel fast to escape the gravitational force BUT when far away, it travels slowly as the sun's gravity pulls it back

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