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Is sum centrifugal force and centripetal force zero?

  1. Dec 13, 2015 #1
    While balancing rotating mass we consider the inertia force (centrifugal force) is equal and opposite to centripetal force which causes the rotation.

    if both force(applied external force on rotating mass) which causes the motion and force which resist motion (inertia force) are equal and opposite, won't they cancel each other and produce nil effect? if so how is the ball rotating with constant angular velocity

    In case of reciprocating mass again we have inertia force which is the mass times the acceleration of reciprocating mass and opposite in direction. if the inertia force and motion causing applied force are equal and opposite, isn't the net force on the body is zero?if not why it is so? and why we consider:
    1. inertial force equal and opposite to the external force applied
    2. what is the real effect of inertia force on a body?
     
  2. jcsd
  3. Dec 14, 2015 #2
    Centrifugal does not exist in a non rotating frame of reference. So you can have centrifugal or centripetal force acting on the ball depending on which frame of reference you choose, rotating or not, but no both together.
     
  4. Dec 14, 2015 #3

    A.T.

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    The inertial centrifugal force exists only in non rotating frames of reference.

    In the rotating frame you have both of them acting.
     
  5. Dec 14, 2015 #4

    A.T.

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    Yes, if you choose a rotating frame of reference, where the acceleration of the body is zero, then centripetal and centrifugal force must cancel.

    In the rotating frame where they cancel, the ball is static.
     
  6. Dec 14, 2015 #5
    okay then in case of reciprocating motion, should we consider inertia force only when we choose a reciprocating frame(non inertia frame)?

    then what effect does the inertia force has on motions? and why do we consider them for balancing of machines and minimizing the vibration?
     
  7. Dec 14, 2015 #6

    A.T.

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    In physics "inertial forces" usually refers to forces that arise only in non-inertial frames. In engineering the term is sometimes used in quasi static analysis of accelerating parts. For a simple system like your ball, the math of these two approaches is indistinguishable.
     
  8. Dec 14, 2015 #7
    we consider inertia force only when we deal with non inertial frame, if so while balancing a machine which has say reciprocating or rotating motion, do we balance it in non inertial frame?
     
  9. Dec 14, 2015 #8

    A.T.

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    I don't know which frame of reference you use to analyze your machine. If you use a non-inertial frame, there will be inertial forces.
     
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