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Question about Torque

  1. Aug 16, 2011 #1
    Out of curiosity, I decided that I would build a Tesla Turbine and possibly use it for some interesting contraption. Except, when I was reading about it, I always heard that it can achieve high RPM, but has low torque.

    I was just wondering if someone would be able to explain the concept of torque, what it does/what it's used for, and what not. I've tried reading up about it, but I'm still having trouble grasping exactly what it's for.

    Thanks, Peter.
  2. jcsd
  3. Aug 17, 2011 #2


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    Power is torque x rpm and a scaling factor that dependes on your units.

    So low torque means the engine may be less suitable for a varying load that drags the rpm down at times.

    This is why diesel engines that have higher torque at low rpms are more common for heavy machines and tractors etc.

    For example a Diesel car engine typically gives peak power at sa 3000 rpm, while a gasoline engine typically gives peak power at 6000 rpm. This is also why in practice, a diesel car at 130 hp is usually perceived as way more powerful than a gasoline car on 130 hp, since you need to whip the gasoline car to scream to get the spec out of it.

  4. Aug 21, 2011 #3
    Torque has to do with coping with the load. Power is always Torque multiplied by rpm. If you want to do work quickly, you would like to have more rpm in the equation, if you want to cope with more load and speed isn't important to you, you gotta have more torque. If you again want to have a heavier load tackled at a higher rate, you gotta step up both rpm value and torque.
  5. Sep 3, 2011 #4
    Torque is analgous to force but deals with rotation. Think of Newtons Second Law, F=m*a. If a net force F is applied to an object of mass m, it will accelerate at acceleration rate of a. Similarily, if a net torque is applied to a rotating system that has a mass moment of inertia of I, it will accelerate at a rate according to T=I*alpha where alpha is the rotational acceleration.

    Engine torque is what causes vehicles to accelerate. If the engine provides torque T to the driven wheel's axle, the force on the pavement that pushes the vehicle ahead is F=T/R where R is the distance from the center of the driving axle to the pavement.

    Horsepower is the rate at which work is being done.
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