Kinetic energy is observable as motion of an object, particle, or set of particles. Examples include the falling of an object in a gravitational field, the motion of a charged particle in an electric field, and the rapid motion ofatoms ormolecules when an object is at a temperature above zeroKelvin.Matter is equivalent to energy in the sense that the two are related by the Einstein equation:E=mc2whereEis the energy in joules,mis themassin kilograms, andcis thespeed of light, equal to approximately 2.99792 x 108meters per second.In electrical circuits, energy is a measure ofpowerexpended over time. In this sense, one joule (1 J) is equivalent to onewatt(1 W) dissipated or radiated for onesecond(1 s). A common unit of energy in electric utilities is the kilowatt-hour (kWh), which is the equivalent of one kilowatt (kW) dissipated or expended for one hour (1 h). Because 1 kW = 1000 W and 1 h = 3600 s, 1 kWh = 3.6 x 106J.Heat energy is occasionally specified in British thermal units (Btu) by nonscientists, where 1 Btu is approximately equal to 1055 J. The heating or cooling capability of a climate-control system may be quoted in Btu, but this is technically a misuse of the term. In this sense, the system manufacturer or vendor is actually referring to Btu per hour (Btu/h), a measure of heating or cooling power.