Usefull Info: Introduction to TORQUE, WORK and POWER

It's been discussed enough times so when I came across this explanation at http://www.chainsandsprockets.co.uk I thought I'd post it.

Torque is the twisting force about a point, sometimes called a 'moment'. The torque is defined as the force multiplied by the distance from the pivot perpendicular to the force. 

Torque = Force x Distance Perp. to Pivot

For example: One foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the pivot. You might directly measure torque when tightening a nut to a specified torque using a torque wrench. Here, a twisting force is applied to the nut, until the resistance to rotation of the nut is equal to the torque required.

Work is the the transfer of energy. The work done is equal to the force applied multiplied by the distance travelled in the direction of that force.

Work =  Force x Distance Travelled

Power is the rate of doing work, the amount of work done in a unit of time. The power produced is the work done divided by the time taken.

	         Force x Distance Travelled
Power = --------------------------
	           Time

For example: If a weight is fixed solidly to the floor and you try to lift it, you are applying force. However the weight cannot move, so no work is done on the weight. Although force is exerted by your arms, no energy is transferred to the weight. If you lift a one pound weight one foot, then by definition one foot pound of work has been done. If you take one minute to do this then you will be producing power at one foot pound per minute. 

One horsepower is 33,000 foot pounds per minute. To find the horsepower of an engine, the torque produced by the engine is measured and the horsepower calculated. This is done using a dynamometer which is essentially a brake with a measuring device - hence the term brake horse power (bhp) which is often used. A torque curve is produced by plotting the torque measured against the engine speed.

With torque in foot pounds:

		       Torque x RPM
Horsepower = 	------------
		         5252

Using this equation a power curve can be produced from the torque curve.

[ophic]

hmmm good tutorial. Being pedantic, and not knowing these imperial measurements too well, it uses the same unit (foot pound) for torque and work. I could swear one of these should be measured in pounds feet.

Originally Posted by ophic

hmmm good tutorial. Being pedantic, and not knowing these imperial measurements too well, it uses the same unit (foot pound) for torque and work. I could swear one of these should be measured in pounds feet.

Hmm, I suspect a foot pound might be one pound foot.

Originally Posted by ophic

hmmm good tutorial. Being pedantic, and not knowing these imperial measurements too well, it uses the same unit (foot pound) for torque and work. I could swear one of these should be measured in pounds feet.

Multiplication is commutative, so the order is irrelevent. If it was pound per feet then it would matter.