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Gravity Inertia

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					          Gravity




Why do planets stay in place?
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                 What is Gravity?
 Gravity is a force of attraction between objects
  – The force of gravity is dependent on the mass of the
    objects and the distance between them.
  – The greater the mass, the stronger is the gravitational
    attraction between the objects
  – The further away the objects are the weaker the
    gravitational attraction.
  – Newton’s law of gravity: F=(G *M1*M2)/r2 the
    force of gravity gets reduced by the square of the
    distances
  – Your weight is the attraction between your mass and
    the mass of Earth
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                Effects of Gravity
 Oceans rise and fall twice daily – called tides.
 Tides are the result of the gravitational pull of the moon
  and sun.
 They pull on the water in the ocean pulling it toward the
  moon, causing a high tide.
 The moon has a greater affect on tides because it is
  closer than the sun.
 Spring tides, the highest high and lowest low tides,
  occur when the moon, Earth & Sun are aligned i.e. a
  new or full moon
 Neap tides- the smallest changes in the tides, occurs
  when the Earth, Sun Moon form a right angle i.e. 1st or
  last quarter moon
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  Orbital Speed & Distance from Sun
 Gravity is the force that holds planets and other
  objects of the solar system in their orbits
 The closer a planet is to the sun, the faster it
  moves. Therefore if we know a planet’s distance
  from the sun we can calculate its velocity.
 Planets with elliptical orbits, move faster when
  they are closer to the sun than when they are
  further away from the sun.


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Inertia & gravity combine to fix orbits
 Inertia – the tendency of an object at rest to stay at rest
  or to keep moving in the same direction it is moving at
  a constant speed
 If a satellite has a circular orbit, inertia and the force of
  gravity are constant. With the change in direction the
  satellite keeps its orbital path. Gravity causes the
  direction to change continuously
 If the orbit is elliptical, gravity also causes the speed to
  change when the satellite is closer to its primary (the
  sun)


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         Gravity & Planet Orbits

   What is Gravity?
   Effects of Gravity
   Orbital Speed & Distance from Sun
   Inertia & gravity combine to fix orbits




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