“Horsepower is how fast you hit the wall. Torque is how far you drive through that wall”
The term “Horsepower” was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.
One horsepower is the power needed to move 550 pounds (249kg) one foot in one second but is also used to calculate electricity 745.7 watts.
James Watt was said to have been working the coal mines with pit ponies and wanted to calculate the output of the animals he was using.
Horsepower is measured at higher RPM’s and torque is the low-end “grunt” or low RPM pulling power of an engine.
Torque is nothing more than a measurement of twisting, or rotational, force. The easiest way to think of this is to imagine a long shaft — like a car’s axle — and imagine it’s in a room suspended in mid air. Hanging on the bottom of one end is a rope with a weight attached — a very heavy weight.
Now imagine someone trying to, using their hands, twist the shaft so as to lift the weight. Think of them as essentially trying to act like a wench and reel it up. The amount of force they are able to generate to lift the weight in this manner is the torque that they’re able to produce. One unit for measurement of this is the foot-pound. A foot-pound is the rotational ‘force’ generated by hanging a one-pound weight at the end of a 1-foot wrench.
Think of that annoying bolt we’ve all had! Often a bolt will be too tight, or rusted on, and you won’t be able to get it loose. If you get a longer wrench, or put a piece of pipe over the handle to make a longer handle, you can exert more torque on the bolt without working so hard, and hopefully it’s enough to loosen the bolt.
Torque – A twisting force
Horsepower – Power, A measurement for work, dependent on torque and RPM.
Acceleration – Dependent on horsepower to weight ratio.
Gearing – A torque multiplier.