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Theory problems!

  1. Jun 22, 2009 #1
    Hi,everyone!
    i have a few queries about various concepts of physics.
    4 d beginning,gravitational force is an attractive force.It increases as the distance decreases.
    Then,why don't the planets collapse with each other??
     
  2. jcsd
  3. Jun 22, 2009 #2

    Astronuc

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    Staff: Mentor

    When posting, please use proper English.

    Planets revolve around much more massive stars. The gravity keeps them from leaving, and the centripetal force of their motion balances the force of gravity, so the planets maintain an orbit. Satellites and spacecraft in orbit around the earth, and the moon orbiting the earth experience the same process.

    In order for a satellite or spacecraft to remain in orbit, it must be traveling at orbital velocity.

    Please refer to - http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html#cent

    http://hyperphysics.phy-astr.gsu.edu/hbase/orbv.html#co
     
  4. Jun 22, 2009 #3
    You can see an orbiting body (let's say a satellite around the earth, but the same applies to the earth around the sun) as a body that is continuously falling toward the earth, but it just keeps missing it!

    There's a well known picture (although I can't find it now) where a bullet or projectile is fired from a (greatly exaggerated) high tower. If the projectile is relatively slow, it simply falls to the ground. When it gets faster and faster however, its trajectory will 'bend' around the curvature of the earth more and more. Eventually, it will get back to the position where it started, having completed one orbit.
     
  5. Jun 23, 2009 #4
    Ok.
    But,the article you referred to says that gravity itself provides the required centripetal force?
    Besides that,orbits of planets are mostly elliptical,not circular.Could you please give more details??
     
  6. Jun 23, 2009 #5
    Alright,but can you please explain this concept in more detail or refer to some website where it is given in detail?
     
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