P5- Satellites, Gravity and Circular motion

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  • Created by: BKDavies
  • Created on: 01-04-16 19:03
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  • Satellites, Gravity and Circular Motion
    • A satellite is an object that orbits a planet in space
      • Natural-the moon
      • artificial-put in space by human e.g. ISS
    • Satellites held in space by a gravitational force.
      • Gravity is a universal force which keeps
        • planets orbiting the sun
        • the moon orbiting the earth
      • Centripetal force acts towards the centre of a circle. It keeps an object moving in a cirlce
        • Gravity provides the centripetal force to keep a satellite in orbit.
    • Weight(N)= Mass(Kg) X Gravitational field strength
    • Gravitational force between objects gets weaker with distance
      • inverse square law- doubled distance, force drops to 0.25
    • Planets close to sun have high gravitational force, compared to those further away
      • Planets closer to the sun travel very quickly
      • Planets further away travel very slowly and have long orbital periods
    • Periodic comets have elliptical loops, which have almost circular orbits
      • when a comet is close to the sun it has to travel quickly to escape the gravitational force
      • when the comet is further away, it travels more slowly because the sun's gravity pulls it back
      • like a tennis ball being thrown in the air- it slows down as it gets higher and speeds up as it gets closer to earth
    • Artificial satellites orbit at different heights above the earth. orbital period increases with height above earth. the height at which it orbits and its period determine what it can be used for
      • low polar orbit
        • travel very quickly, go round the earth several times a day
        • uses are imaging earth's surface, weather forecasting and military uses (spying)
      • Geostationary  satellites
        • orbit much higher above the earth, take 24 hours to complete one orbit, remain above a fixed position on the eath's equator
        • Uses are communications ( satellite television), weather forecasting
      • Satellites can also be used for scientific research and GPS
  • satellite would normally travel in a straight line
    • Earth' s gravitational force causes it to continually accelerate towards earth and prevents it flying off at a tangent
      • two effects balance causing the satellite to remain in a circular orbit
      • speed of a satellite in low orbit must be high enough to balance the the gravitational fore and keep them going in a circle
    • Artificial satellites in low polar orbits feel strong gravitational force dragging them towards earth, so they travel faster than those in high orbits
    • Geostationary satellites are in high orbits so the gravitational force is weak. they move more slowly and have further to travel.


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