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I What force keeps a radially accelerating object in the air?

  1. May 4, 2016 #1
    So in my physics class this last semester, we learned about normal force, weight and centripetal acceleration and all that good stuff. So i got to thinking about a ball on a string being spun around my head and i got to thinking about the force diagram you would draw for that, and obviously you would have your force due to the acceleration of gravity (weight) pointing down, the Force of tension pointing inwards, and....? since the ball has zero acceleration in the Y direction then there must be an equal but opposite force to the weight. The only possible force i could think of is that i am not spinning the ball on soleley in the horizontally, but i am applying the force to the string in a slightly upward direction. Any direction would be appreciated. thanks for reading.
  2. jcsd
  3. May 4, 2016 #2


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    Staff: Mentor

    You are indeed correct. :biggrin:
  4. May 4, 2016 #3


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    Gold Member

    This is similar to the problem of hanging a weight on a washing line. Its not possible to tension the line enough to make it perfectly horizontal with no sag. The required tension approaches infinity as the angle of sag approaches zero.
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