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B What is a moment

  1. Mar 1, 2016 #1
    Hi,
    I'm currently learning about moments and equilibriums. I'm able to solve the problems quite properly, like determining different forces, distances and etc. what intrigued me is that when we say that an object has a moment of 1700 Nm about point o. Does it mean that the object will provide that much rotation from the axis in terms of the distance or does it have another implication? Can the degree of rotation be deteimed from An objects torque? Because when I imagine the motion of a stick from a certain point I don't see it rotate 360 degree simply because the force acting on it is not consistent. For example adding a weight to propellers side won't make it spin completely but if I keep adding weight to every side that comes up after each rotation it will make a complete rotation. Am I correct? Then what exactly does the moment or a torque on an object tell us?
     
  2. jcsd
  3. Mar 1, 2016 #2

    Hesch

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    Gold Member

    In the below figure, the torque = distance * force will rotate the nut.
    upload_2016-3-1_18-48-26.png

    Generally, a torque will try to rotate something. A rotating motor will yield torque to its shaft.
     
  4. Mar 1, 2016 #3
    Torque can be thought of in units of Joules per radian. What this tells us that a constant torque of 1 Joule/radian will transfer to an object an energy (manifest as rotational kinetic energy) of 1 Joule for every radian of resulting rotation. In simpler terms, a torque is a turning force.

    So with a stick in your hand, it will not rotate 360 because you are not applying a constant torque. But certain mechanisms can. Even simple mechanisms can do so, at least approximately. For example:

    A rubber band powered car.
     
    Last edited: Mar 1, 2016
  5. Mar 1, 2016 #4

    CWatters

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    Science Advisor
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    Perhaps compare....

    Force = mass * acceleration
    with
    Torque = moment of inertia * angular acceleration
     
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