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A unit of electrical energy, particularly for utility bills, is the kilowatt-hour (kWh); [3] one kilowatt-hour is equivalent to 3.6 megajoules. Electricity usage is often given in units of kilowatt-hours per year or other periods. [4] This is a measurement of average power consumption, meaning the average rate at which energy is transferred ...
So the energy equivalent of one kilogram of mass is 89.9 petajoules; 25.0 billion kilowatt-hours (≈ 25,000 GW·h) 21.5 trillion kilocalories (≈ 21 Pcal) [note 4] 85.2 trillion BTUs [note 4] 0.0852 quads or the energy released by combustion of the following: 21 500 kilotons of TNT-equivalent energy (≈ 21 Mt) [note 4]
This creates a limit to the amount of heat energy that can do work in a cyclic process, a limit called the available energy. Mechanical and other forms of energy can be transformed in the other direction into thermal energy without such limitations. [14] The total energy of a system can be calculated by adding up all forms of energy in the system.
A human in a sprint has approximately 3 kJ of kinetic energy, [20] while a cheetah in a 122 km/h (76 mph) sprint has approximately 20 kJ. [21] One watt-hour, of electricity or any other form of energy, is 3.6 kJ. megajoule The megajoule is approximately the kinetic energy of a one megagram (tonne) vehicle moving at 161 km/h (100 mph).
For example, when a light bulb with a power rating of 100 W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours.
The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy of a fuel per unit mass is called its specific energy . The adjacent figure shows the gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article).
Energy conversion, process of converting energy from one form to another; Dark energy, used to explain some cosmological phenomena; Energy quality, empirical experience of the characteristics of different energy forms as they flow and transform; Energy density, amount of energy stored in a given system or region of space per unit volume, or per ...
A kilowatt is a unit of power (rate of flow of energy per unit of time). A kilowatt-hour is a unit of energy. Kilowatt per hour would be a rate of change of power flow with time. Work is the amount of energy transferred to a system; power is the rate of delivery of energy. Energy is measured in joules, or watt-seconds.