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B Forces opposing rotary motion other than Inertia

  1. Aug 22, 2016 #1
    Hello Gurus,

    What are the forces opposing rotary motion? And how to calculate them?
    For eg., if we have a shaft rotating about it's own axis, are there any other forces that oppose this motion other than bearing friction, like air resistance or some other forces. And how to calculate these forces if we know the mass of the shaft.

    Thanks in advance for your valuable answers.

    Sireesha Ch
  2. jcsd
  3. Aug 22, 2016 #2


    Staff: Mentor


    Air resistance depends on the size and shape of the shaft, not its mass.

    Other forces might be magnetic, such as in an electric motor. A motor spins somthing (called the load) that opposes rotation. Magnetic forces push the rotation. In an electric generator, things are reversed. Something mechanical, like a turbine rotates the shaft and magnetic forces oppose it.
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