The equivalent of, or the capacity to perform, mechanical work, the difference between two states of
thermodynamic entropy before ad after work has been performed. Energy is measured either as the product of force and distance (e.g., in lifting a weight a certain height) or as the product of power and time (e.g., in getting an object to move with a certain speed). Energy may be stored in a material form as in the momentum of a wheel or of a bullet in motion. Electrical energy is measured in kilowatt/hours (kw/h), heat energy in Calories or in British thermal units (Btu), mechanical energy in horsepowers, light in Joules, explosives in tons of TNT, etc. Different forms of energy are inter-convertible due to the
first law of thermodynamics which makes energy the most important
construct of physics. All physical processes including
computation and
communication are known to require energy (
see thermodynamics ). (
Krippendorff )
