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Gear head

Horsepower and Torque



by Steve D’Antonio In part one of this two-part series I discussed horsepower, its characteristics, and the measurement thereof. In part two, we’ll take a closer look at horsepower’s cousin, torque.


ike horsepower, torque is also a measure of energy. However, it has nothing to do with time; it could be imparted over one minute or one year. If horsepower is energy measured over time, torque could be thought of as the process for transforming or converting that energy into a useful motion, one that twists, as an axle or propeller shaft.

The definition of torque can be a bit difficult to enables you to subject the fastener to 20 poundgrasp. For illustrative purposes, imagine torque is feet of torque or 27 Newton meters. It’s one of simply a force in pounds multiplied by distance. those rare cases where Mother Nature seems to be You’ve almost certainly demonstrated this yourself offering up a free lunch. by using a longer wrench or an extension pipe Engine torque is measured using the following slipped over a socket formula: (5,252 x hp) wrench (the “exten÷ rpm. In order to get ##Traditional diesels provide significant sion” is used in this more power from an torque at low rpm by relying on large case on the handle; engine, and because displacement cylinders, equating to it should not be conhorsepower is a meagreater size and overall engine weight. fused with extensions surement of power used on the driven over time, it would or socket end of the seem then that one wrench) when removway to squeeze more ing a stubborn nut or of that power from bolt, or a piece of pipe an engine would be used on the handle to make it turn faster. of a stiff seacock. The In fact, this approach extension multiplies works well. It’s why the torque applied to the small, light-yetthe fastener by virtue powerful engine on of the length or dismy Italian motorcycle tance that the force is spins up to 8000 rpm, applied by your hand to develop more from the point where power from a smaller it’s applying twisting power plant package. motion. That isn’t a free lunch; Ten pounds of turning engines at force applied to a higher speeds comes one-foot long wrench with its own set of imparts 10 poundside effects: increased feet (it’s pound-feet in wear, decreased lonthis case by the way, gevity, and increased not foot-pounds, which represents work or an cost of engineering to name just a few. expenditure of energy) of torque, or 13.5 Newton Math-minded folks will have noticed in the meters/Nm in the metric system, while 10 pounds above formula that as rpm increases, torque of force applied to a two-foot long extension decreases, and there goes the free lunch, yet again. Follow us! October 2015 35

PropTalk Magazine October 2015  

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