Work

The Kinetic energy, internal energy, potential energy, and P-V energy are kinds of energy which are properties of a system. The work is a form of energy, though it is energy in transit. The work is not a property of a system. Work is a procedure done by or on a system, though a system has no work. This difference among the forms of energy which are properties of a system and the kinds of energy which are transferred to and from a system is significant to the understanding of energy transfer systems.

The work is defined for mechanical systems as the action of a force on an object via a distance. It equivalents the product of the force (F) times the displacement (d).

W = Fd

Here:

W = work (ft-lbf)

F = force (lbf)

d = displacement (ft)

In dealing with work in association to energy transfer systems, it is significant to differentiate among work done by the system on its surroundings and work done on the system by its environment. Work is done by the system whenever it is used to turn a turbine and thus produce electricity in a turbine-generator. Work is done on the system whenever a pump is employed to move the working fluid from one position to the other. A positive value for work points out that work is done by the system on its surroundings; a negative value points out that work is done on the system by its surroundings.