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Find the critical rotation rate

  1. Sep 17, 2014 #1
    1. The problem statement, all variables and given/known data

    The tumbler in an upright clothes dryer rotates at a critical angular
    velocity so that clothes passing over the top briefly experience weightlessness.
    If the radius of the drum is 0.30 m, what is this critical rotation rate? (Express
    your answer in both radians per second and revolutions per min (RPM).) At
    this rate, what is the apparent gravity felt by the clothes when they pass over
    the bottom? (Express your answer in multiples of g.)


    2. Relevant equations

    arad=v2/R



    3. The attempt at a solution
    I don't see how we can extrapolate a critical rotation rate from the given equation. Maybe I am just missing something or are we looking for Vf?
     
    Last edited: Sep 17, 2014
  2. jcsd
  3. Sep 17, 2014 #2

    gneill

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    Staff: Mentor

    Consider what the term "weightlessness" means and implies with regards to net acceleration.
     
  4. Sep 17, 2014 #3

    mfb

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    2016 Award

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    You'll need the angular velocity for the answer, but you can start with the velocity if you like.
    There is no need to extrapolate anything. When do you get weightlessness?
     
  5. Sep 17, 2014 #4
    You get weightlessness when g=0
     
  6. Sep 17, 2014 #5

    gneill

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    But g is not zero. It's a constant 9.8 m/s2. What other acceleration is in play? What's the net acceleration?
     
  7. Sep 18, 2014 #6
    Well we care about the acceleration of ω right?
     
  8. Sep 18, 2014 #7

    mfb

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    ω is constant, there is no "acceleration of ω". There is an acceleration that has a relation to ω, yes.
     
  9. Sep 18, 2014 #8
    Perhaps "weight" can be thought of as normal force exerted on the body.
     
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