Work, in physics, the movement of a body by a force acting against a resistance. Work is performed when a person lifts a weight, since the person applies a force to move the weight upward. However, no work is done by a person who simply holds the weight above the ground, even to the point of exhaustion. If the weight is allowed to drop, gravity does work by giving the object a downward velocity.
Work is done whenever energy is transferred from one body to another and the second body is moved against a resistance. When a box is pushed up an incline, the box is moved against three kinds of resistance: (1) inertia, the resistance of a body to a change in motion; (2) gravity, which resists movement to higher levels; and (3) friction, the resistance to sliding motion that exists between two bodies in contact.
Work is measured by multiplying the force by the distance through which it moves. Force is the push or pull that produces a change in motion. It can be measured in two ways: (1) in gravitational units, such as the pound-force and gram-force; or (2) in absolute units (which are free of the varying influence of gravity), such as the poundal and newton.
In Gravitational Units. When one pound of force (one pound-force) acts through a distance of one foot, one foot-pound of work is done. Another gravitational unit is the gram-centimeter.
In Absolute Units. The amount of work done by a force of one poundal acting through a distance of one foot is one foot-poundal. In the metric system, the absolute unit of work is the joule, equal to the force in newtons multiplied by distance in meters. The erg is another absolute unit of work in the metric system; one joule equals 10,000,000 ergs.
Work is related to energy and power. Energy is the ability to do work. Power is the rate at which work is done. A machine is a device by which force is applied to do work.
