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Homework Help: Centrifugal force versus gravity (ball on a joint placed on rotating shaft)

  1. Sep 13, 2010 #1
    1. The problem statement, all variables and given/known data

    Basically, this is the problem.

    [PLAIN]http://img180.imageshack.us/img180/3598/physicsproblem.png [Broken]

    It's related to some design research I'm doing regarding a centrifugal control valve. This is a type of valve that controls the fluid flow based on the centrifugal force that effects the weigths strapped onto the valve shaft. The higher rpm (the shaft is connected to a small turbine powered by the fluid flow), the higher centrifugal force, and the higher the ball should raise (in actual case, connected with the valve disc, but lets ignore that in this ideal case). Now, I'm trying to calculate the neccesary rpm value for a desired angle of the joint holding the ball from vertical line. Ideal system.

    2. Relevant equations

    Did I setup the problem correctly? Can this be observed as a static problem as I did? What am I doing wrong? I see if the angle increases toward the value of 90, the neccesary rpm goes into infinity. Is this normal?

    Thank you.

    3. The attempt at a solution

    My attempt is included in the picture.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 13, 2010 #2


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    LachieD: If the input units for n are Hz, post 1 currently looks correct.
  4. Sep 14, 2010 #3
    Yeah, that is correct. Thanks. I was just wondering if the problem was setup correctly.
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