2: Energy
- Page ID
- 56754
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“Energy” is an extremely loaded term. It is used in everyday parlance to mean a number of different things, many of which bear at most a passing resemblance to the term as used in physical science.
At its core, energy is a mathematical construct that has turned out to be extremely useful. It shows up always with the same dimensionality, but in different forms. In a physical system, you can identify the forms of energy that are present, and calculate a number that represents the amount of energy there is for each of these forms. Ultimately, though, energy is just a mathematical construction that we calculate. What makes it so useful, however, is the observation that in all successful theories of physics thus far, energy is conserved. We could just as easily name and calculate an unending variety of other quantities for physical systems, but few are quite so useful as energy. If you take into account all of the various forms of energy in a complete system, you neither create nor destroy it. That is, in any interaction, the total amount of energy afterwards is exactly the same as the total amount of energy beforehand. Any energy lost by any part of the system must have been gained by another part of the system, and vice versa.
- 2.1: The Units of Energy
- The SI unit for Energy is the joule, usually abbreviated J. One joule is equal to one kilogram meter squared per second squared:
- 2.2: Forms of Energy
- There are a number of forms of energy, but most of them can be reduced to either kinetic energy (energy of motion) or potential energy (energy of relative position). These two are discussed in greater detail below.