energy

The physics concept of energy is a type of measurable quality of an object or system that is needed to make something happen. The physics concept of energy is something that is permanent (conserved): its loss is merely its transfer it to something else or its transformation into some other kind of energy. For example, to lift an object of a certain mass from the ground to a certain height above ground requires a certain amount of energy. (The same amount of energy remains; afterward, the energy that lifted it remains inherent in the separation of the mass from the ground.) Among the forms of energy:

• heat.
• kinetic energy (inherent in the motion of something).
• potential energy (inherent in separated pairs of objects with a force between them, e.g., gravity).
• chemical energy (e.g., turned to heat when something burns).
• nuclear energy (the binding energy of an atomic nucleus).
• mass (of things, per e=mc²).
• radiant energy (that which is carried by EMR).

The physics term work is such transformation of energy, which is quantified by units of energy, i.e., the amount transformed. Energy as we know it everyday generally came from the Sun in the form of electromagnetic radiation (EMR), generally converted by plants into chemical energy, and by its heating effect on weather and climate. Numerous units are used to quantify energy in science and everyday life. Some of them:

For context, a joule is very roughly the energy to lift (in Earth surface gravity) a pound weight 9 inches, or a kg weight 10 cm. Because of the relation between energy and mass (e=mc²), any unit of energy can be used as a unit of mass and vice-versa. Electron volts are perhaps used as measures of mass as much as they are of energy. The physics term for the rate at which energy is transformed (work is done) is power. Luminosity is basically power, but the term is used for measures of EMR emitted by a body, and for the extraction of nuclear energy used to produce that emission. Some units of power: