DEFINITIONS

Workis the act of producing a change of configuration in a system in opposition to a force which resists that change.

Energyis the capacity of doing work.

When the nature of a material system is such that if, after the system has undergone any series of changes, it is brought back in any manner to its original state, the whole work done by external agents on, the system is equal to the whole work done by the system in overcoming external forces, the system is called a Conservative system.

PRINCIPLE OF CONSERVATION OF ENERGY

The progress of physical science has led to the discovery and investigation of different forms of energy, and to the establishment of the doctrine that all material systems may be regarded as conservative systems, provided that all the different forms of energy which exist in these systems are taken into account.

This doctrine, considered as a deduction from observation and experiment, can, of course, assert no more than that no instance of a non-conservative system has hitherto been discovered.

As a scientific or science-producing doctrine, however, it is always acquiring additional credibility from the constantly increasing number of deductions which have been drawn from it, and which are found in all cases to be verified by experiment.