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Lifting/breaking an object with circular motion

  1. Mar 4, 2012 #1
    i have two questions i think are asking almost the same thing.

    1) in this typical centripetal force experiment; there are a stopper mass attacthed to one end of a rope and a washer attached to the other end of the rope. as the washer hangs straight down, i start whirling the stopper. after a point, the faster i whirl it, the more the washer goes up. the question is what is the force that pulls the washer upwards? i assume the tension must always be equal to the centripetal force that is created by the weight of the washer so it shouldnt be enough to beat the weight of the washer to lift it.

    2)there is a nut or something breakable on an end of a rod and as you whirl the rod vertically keeping the nut in a circular motion. as you do it faster and faster you observe the nut breaks or at least gets damage soon or later. what is the force that breaks the nut?

    thanks.
     
  2. jcsd
  3. Mar 4, 2012 #2

    Doc Al

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    Staff: Mentor

    The string tension.
    Don't assume that the tension just equals the weight of the washer. By spinning the stopper faster, you create more tension, which raises the washer.
    The faster you whirl the rod, the greater force it must exert on whatever is attached to it. Eventually, something breaks.
     
  4. Mar 4, 2012 #3
    how do i creat more tension with no additional force? and obviously as the washer goes up it gains some more potential energy so there has got to be a net force that does some work against gravity by raising the washer?
    i can actually put it that way what force makes the rope break when i whirl an object attachted to the rope fast enough? lets say vertically and above my head.
     
  5. Mar 4, 2012 #4

    Doc Al

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    Staff: Mentor

    Tell me how you get the stopper to go faster.
    When the string tension gets too high, the string breaks. You are pulling on the string with a greater force as you twirl it faster.
     
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