Work is the measurement of energy transfer that takes place when an object is displaced by an external force applied in the direction of the displacement.
The rate of doing work is called power.
The capacity for doing work is called Energy. It may exist in kinetic, potential, thermal, chemical, electrical, nuclear, or various other forms. The SI unit of energy is the same as that of work.
Principle of Conservation of Energy: The Principle related to the conservation of mechanical energy states that the total mechanical energy of a substance remains in equilibrium if the only forces acting upon the body are conservative in nature.
Law of Conservation of Energy: Energy can neither be created nor be destroyed, however, it can be changed from one to another form. The total energy in an isolated system remains the same or energy is conserved over time. The mass remains the same in any closed system within boundaries except for the heat form which can cross boundaries.