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Torque question

  1. Feb 22, 2016 #1
    The definition of torque is τ= r x F

    Let's consider a disk that is rotating around his axis of symmetry, we are usually used to calculate the torque applied by a tangential force at the disk using as r the radius of the disk, but can I define a torque of the force using as r the generic distance between a point external of the disk? In this case will be the torque by this point different by the one referred to the axis of rotation? In my opinion yes because it's the most logical thing

    Can we define a torque in a non rotation situation? Think at a particle that is pulled by a force in a uniform accelerated motion, according to the definition of torque we can choose a point in space and get the distance between that point and the force and get a torque, is that right?
  2. jcsd
  3. Feb 22, 2016 #2


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    Yes, the definition of torque says noting about rotation.
  4. Feb 23, 2016 #3
    one can define a torque from taking radius vector from the axis and the force vector applied at a point on the body- as its a vector product the torque will generate a rotation due to application of the force. so you can not say that its a non rotational system.
  5. Feb 25, 2016 #4
    The answer to the first question is "yes" -- this is what happens every time a wrench is used to turn a bolt or a nut; the force is applied at some distance external to the bolt head or nut.
    The answer to the second question is, "it depends" -- the same force (F) applied to a longer lever-arm (r) will yield a proportionally greater torque. Said another way, a longer lever-arm allows the same torque to be developed with proportionately less force.
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