quantitative property of a physical system, recognizable in the performance of work and in the form of heat and light From Wikipedia, the free encyclopedia
Energy can mean various things:
In physics, energy is a property intrinsic to anything that is able to interact in the universe. The energy of an object is its capability of producing a force that can do work, as well as its capability of transferring heat. When an object does work on another object (changing its momentum), the former’s energy (its capability of doing work) decreases and the latter’s energy increases, by transferring it.
Basic forms of energy include:
Energy is a property that is not created or destroyed, although energy can change in detectable form.[1] This is a rule that is commonly understood as the "conservation law of energy". In respects to this rule, the total amount of energy that exists in an isolated system will always be the same, no matter what changes have been made to it.
In the early 20th century, scientist found that matter itself can be created from energy (energy and matter are interchangeable, in spite of everyday experiences). This is just another change of form. After these discoveries, the conservation law of energy was extended to become the conservation law of matter and energy: matter and energy can neither be created from nothing nor destroyed to the point of complete erasure from reality. Albert Einstein was the first to mathematically show this. (E = mc2)
Matter can be created from energy or converted into energy through processes such as nuclear fission or nuclear fusion.
Scientists have identified many types of energy, and found that they can be changed from one kind into another. These include:
For example:
Energy can be measured. The amount of energy a thing has can be given a number.
As in other kinds of measurements, there are measurement units. The units of measurement for measuring energy are used to make the numbers meaningful.
The SI unit for both energy and work is the joule (J). It is named after James Prescott Joule. 1 joule is equal to 1 newton-metre. In terms of SI base units, 1 J is equal to 1 kg m2 s−2. It is most often used in science, though particle physics often uses the electronvolt.
The measurement for electricity most often uses the kilowatt-hour (kW·h). One kW·h is equivalent to 3,600,000 J (3600 kJ or 3.6 MJ).
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