Man's physical universe






Energy is the active agent behind any force, maintaining the force

and causing it to do work. Although it is the most comprehensive

and fundamental concept of physical science, it cannot be adequately

defined. The scientist usually thinks of energy as that which may be

converted into work.

Power Is the Rate at Which Work Is Done.

Work is the product of a force and the distance through which an object

is moved by the force. Whenever an object is moved by a force, work

is done; the farther the object is moved and the greater the force

required, the more is the amount of work done.

An important consideration in using machines is the rate at which

they do work, which is the definition of power.

James Watt, when working on his steam engine, was forced to

measure the power of his engine and invented the horsepower as the

unit of work. A horsepower is now accepted as the power required

to lift

vertically 550 pounds one foot in one second.

Machines, like animals, do not always work at their maximum rate.

Thus a 2000-h.p. airplane motor may be called upon to deliver that

amount of power only under conditions of maximum climbing with

maximum loads. A 3^-h.p. electric motor does not consume any

more electricity than a 3^-h.p. motor when it is doing work that

requires only 3^^ h.p. It is a general rule that machines should be

capable of delivering much more power than they are usually called

upon to deliver because such machines will last longer and develop less


No man could work at his highest speed for any considerable

length of time, as is evidenced by the exhaustion of a runner at the

end of a race.

Electrical power is usually measured in watts or kilowatts; 1 kilowatt

equals 1.34 horsepower.


More magazines by this user
Similar magazines