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Noob needs help

  1. Dec 7, 2004 #1
    Im an aussie in yr 10 pathway 1 physics, so im no newton.

    However, does newtons 1st law apply to a satellite and if so, how?(u don't have to anwer the how).

    Remember please keep it fairly simple. :yuck:
    Last edited: Dec 7, 2004
  2. jcsd
  3. Dec 7, 2004 #2


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    Newton's first law applies only to bodies which are either isolated,meaning the interaction with other bodies is absent/may be consiedered neglecteble,or it interaction with bodies,so that the the vector sum of all forces applied on the body by external bodies is nil.It's the case for the satellite,where are only 2 forces acting on the satellite:the centrifugal force and the (earth's attraction) gravitational force.Since the satellite rounds on a stabile orbit,you might say that it is equilibrium ans so,the first principle would apply.So the satellite would move around earth on an stable velocity.Those satellites are called "geostationary",since their angular velocity is the same as earth's.

  4. Dec 7, 2004 #3
    No, Newton's first law doesn't apply to satellites. The first law states that if the force applied over a body is null (or the sum of all forces applied are null) that body remains in rest or moving in straight line with constant speed.

    In this case our satellite is orbiting, so there's a net force that keeps it moving that way. That's the gravity. It's a common misconception think in centrifugal force as a real force acting over the body. If it were a centrifugal force that canceled the effect of gravity, what prevents the satellite to keep moving in a straight line?

    I hope my explanation is clear to you.
  5. Dec 7, 2004 #4


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    My mistake,sorry.The centrifugal force is an inertial force (hence the name) and it appears only in the earth's frame if reference.In the satellite's (which provides an inertial frame of reference) there are no inertial forces.The only one that acts is gravity.Silly me... :yuck: I'm ashamed of myself...
  6. Dec 8, 2004 #5
    Gee Wizz Thnx

    Hey Thnx that just saved me around 4 nights of constant migrains and sleep deprivation :biggrin:
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