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Torque units question

  1. May 1, 2009 #1
    Dear Physics Gurus, o:)

    I am trying very hard to understanding the units used to measure torque.

    I know there is a unit called kilogram force centimeter, and 1 ounce force inch = 0.072007790632 kg force cm.

    My problem is I do not understand what these units mean. I could only find definition for Kilogram-force and not Kilogram-force-cm.
    for example: http://en.wikipedia.org/wiki/Kilogram-force

    How much weight can a motor lift if it is rated 3.6 kg force cm and also rated at 200 rpm? Does it mean it can lift a maximum of 3.6 kg at a speed of 200 rpm? And how many centimeters will it lift per minute?

    As you can see, i am kinda confused :confused: and cannot 'feel' how much weight can be lifted given the torque unit of kg force cm.

    Please could you help me.

    Best regards
  2. jcsd
  3. May 1, 2009 #2
    Torque = Force x moment arm
    In your case, consider 3.6 kg force with a 1.0 cm moment arm (you could use any combination - I picked this one only to make it easy).
    3.6 kg force = 35 N
    1.0 cm = 0.01 m
    So, you have 0.35 Nm of torque.
    How you use that torque is up to you. You can now use a pulley with r = 4.0 m and you can lift 0.35 Nm/4.0 m = 0.088 N, or you can use a pulley with r = 0.12 m and you can lift 0.35 Nm/0.12 m = 2.9 N. The difference will be the velocity with which you can lift.
  4. May 1, 2009 #3
    Here is a sample of how to use torque in Newton meters (Nm) on your car engine

    Power (watts) = torque (Nm) x RPM x 2 pi/60
    Horsepwer = watts/746

    Example 100 Nm torque and 2200 RPM = 23,038 watts = 30.9 HP
  5. May 2, 2009 #4
    Dear TVP45,
    Thank you very much for your explanation which has fully clarified my doubt. I am very greatful.

    Thanks also to Bob S for the useful example.


    Best regards
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