But what is horsepower, and what does the horsepower rating mean in terms of performance? In this article, you'll learn exactly what horsepower is and how you can apply it to your everyday life. The term horsepower was invented by the engineer James Watt. Watt lived from to and is most famous for his work on improving the performance of steam engines.
We are also reminded of him every day when we talk about watt light bulbs. The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22, foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33, foot-pounds of work in one minute.
It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner. What horsepower means is this: In Watt's judgement, one horse can do 33, foot-pounds of work every minute. So, imagine a horse raising coal out of a coal mine as shown above.
A horse exerting 1 horsepower can raise pounds of coal feet in a minute, or 33 pounds of coal 1, feet in one minute, or 1, pounds 33 feet in one minute. You can make up whatever combination of feet and pounds you like. As long as the product is 33, foot-pounds in one minute, you have a horsepower. You can probably also imagine that you would not want to put 1 pound of coal in the bucket and ask the horse to run 33, feet in one minute, since that translates into miles per hour and horses can't run that fast.
However, if you have read How a Block and Tackle Works , you know that with a block and tackle you can easily trade perceived weight for distance using an arrangement of pulleys. So you could create a block and tackle system that puts a comfortable amount of weight on the horse at a comfortable speed no matter how much weight is actually in the bucket. If you want to know the horsepower of an engine , you hook the engine up to a dynamometer.
A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load. Similarly, if you attach a shaft to an engine, the engine can apply torque to the shaft.
A dynamometer measures this torque. You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine , put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds.
You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7, rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6, rpm and record the load there.
Then you apply additional load to get it down to 6, rpm, and so on. You can do the same thing starting down at or 1, rpm and working your way up.
If you plot the horsepower versus the rpm values for the engine, what you end up with is a horsepower curve for the engine. Mathematically speaking, horsepower is the force needed to move pounds one foot in a second, or 33, pounds one foot in a minute.
Horsepower is found by measuring torque because torque is easier to calculate. Torque, as previously mentioned, is the expression of a twisting force and is measured in units of force times distance from the axis of rotation. So for instance, if you use a 1-foot-long wrench to exert a force of 10 pounds on the end of a bolt, then you are applying a torque of 10 pound-feet 10 lb-ft.
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This explains why a race car and a tractor that have the same amount of horsepower can vary so drastically. In a race car, all the torque is used for speed through the gearing, whereas the tractor converts the horsepower into pushing and pulling extremely heavy weights. Another way to understand horsepower vs. When you are using all your strength to open the jar, you are applying torque—regardless of whether or not the cap comes off. What is horsepower? Here, we take you through everything about engine power you need to know.
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