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I Physics Behind a Fan

  1. Jun 26, 2017 #1
    Fan makes me wonder the Vicinity of Physics. The fan is rotating at an anti-clockwise direction & it is suspended from the ceiling by a cylindrical handle. Now the fun starts here...

    According to Newton's 3rd law every action has its opposite reaction. That means the anti-clockwise angular momentum of the fan should produce a clockwise torque on its handle which will make the handle unstable & forces the fan to fall down.

    But this never happens why?
     
  2. jcsd
  3. Jun 27, 2017 #2

    rcgldr

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    Homework Helper

    At steady state (not accelerating), the motor exerts an anti-clockwise torque on the fan, the fan exerts an anti-clockwise torque on the air related to drag. The air exerts a clockwise torque on the fan, which in turn exerts a clockwise torque on the motor, which in turn exerts a clockwise torque on the handle, which in turn exerts a clockwise torque on the ceiling (the "ceiling" would exert an anti-clockwise torque on the handle).
     
  4. Jun 27, 2017 #3

    russ_watters

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    Staff: Mentor

    Constant angular momentum does not produce torque; the drag of the fan against the air is what produces the torque.
    It isn't much torque.
     
  5. Jun 28, 2017 #4
    Thanks
     
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