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Centrifugal force around planets

  1. Apr 28, 2009 #1

    When I thought about centrifugal force, gravity came into my mind...

    When we tie a rope around a ball and rotate it in the air, rope gets some tension ( small displacement between atoms of rope ) and we feel this as centrifugal force. This force occurs because we apply an electromagnetic force to the electrons of the atoms around the ball by the electrons of the rope. but we don't apply the same force to inner atoms of the ball so inner atoms tend to go slightly outwards from the center of the ball and cause a small displacement withing the ball. it is that displacement that we feel as tension and centrifugal force. ( correct me if I am wrong... )

    But things differ with gravity. gravity goes and reaches to ALL the atoms of a planet when it is in orbit. and gives every atom the same acceleration ( tidal effects ignored ). orbiting a planet is like a continous free fall. if every atom gets the same acceleration, distances between the atoms will not change and therefore we won't be able to measure any tension on the planet.

    So my question is; do we really feel an outwards centrifugal force when we are in orbit?
  2. jcsd
  3. Apr 28, 2009 #2


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    Science Advisor

    That's centripetal force. It acts through the rope, and is different from gravity. It's simply a force.
    Centrifugal force acts on every single bit of matter, exactly like gravity. Both, gravitational force and centrifugal force, are fictional forces. They vanish if you calculate things in a local inertial frame, where F=ma.
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