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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
    Ramone
     
  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.

    Cheers!

    Best regards
    Ramone
     
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