Work is the overcoming of resistance through a certain distance. It is measured by the product of the resistance into the space through which it is overcome, thus:
| work = distance × space |
For instance, in lifting a body from the earth against the attraction of gravity, the resistance is the weight of the body, and the space, the height to which the body is raised, the product of the two being the work done.
The unit of work is the foot pound, which is the amount of work done in overcoming a pressure or weight equal to one pound through one foot of space.
The unit of power is the horse power which is equal to 33,000 foot pounds of work per minute, that is:
| horse power = | foot pounds per minute |
| 33,000 |
The unit of power was established by James Watt as the power of a strong London draught horse to do work during a short interval, and used by him to measure the power of his steam engines.
In order to measure the mechanical power of a motor, it is necessary to first determine the following three factors upon which the power developed depends:
1. Pull of the armature, in pounds;
2. Distance in feet at which the pull acts from the center of the shaft;