Gregory Loy, Age 14, of Rockford, Ill., for his question:
What is meant by horsepower?
The word makes you think of a sturdy hors, toiling with all his might. Then you learn that the capacity of an engine is measured in horsepower and you wander . How the sturdy animal fits into the picture. Machines and horses seem to be far apart. Nevertheless, a sturdy draft horse played the star role in the story of horsepower.
The age of machinery began about 200 years ago and the Scottish inventor, James Watt, did a great deal to help it on its way. His mechanical gadgets made the steam engine workable. Watt was a practical man, a true mechanic interested in getting the best out of his engines. His practical nature led him to develop the horsepower.
In mechanics, the word power has a special meaning. It is a combination of energy and speed. A strong man and a boy could each move a house, brick by brick. Both would spend the saws amount of energy to do the job. But the man could do the work in perhaps half the time. In this case, the man would have twice as much power as the boy.
When James Watt was working on his engines, he needed a unit to measure power. He also wanted to sell people on the idea of machinery and it seemed a good idea to compare the working ability of an engine with the working ability of a horse.
He based his unit on the amount of work a strong draft horse could do in one minute. Sere people think he overestimated the power of a horse, for his unit is equal to the capacity of about one and one third horses. Perhaps the horse he used was a very superior animal.
The horsepower can be estimated in foot pounds. The foot pound is a measure of energy used, disregarding the time it takes to do the work. One foot pound is the amount of energy expended to lift a pound weight one foot from the ground, regardless of time.
One horsepower is equal to 33,000 foot pounds per minute. Watt estimated this to be the work capacity of a strong draft horse. A strong man can lift 33,000 foot pounds in ten minutes, which gives him a capacity of one tenth of a horse power. An engine that can do this amount of work in a second has a capacity of 60 horsepower.
The name of James Watt was honored when time came to work out the units of electrical power. The watt is a small unit of the amount of work an electrical appliance can do in one second. The horsepower is equal to 746 watts. The kilowatt is equal to 1,000 watts or 1.34 horsepower.