Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information.... |
Home Conservation Laws Simplifying the Energy Zoo All Energy is Potential or Kinetic | |||||||
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All Energy is Potential or KineticIn the same way that we found that a change in temperature is really only a change in kinetic energy at the atomic level, we now find that every other form of energy turns out to be a form of potential energy. Boiling, for instance, means knocking some of the atoms (or molecules) out of the liquid and into the space above, where they constitute a gas. There is a net attractive force between essentially any two atoms that are next to each other, which is why matter always prefers to be packed tightly in the solid or liquid state unless we supply enough potential energy to pull it apart into a gas. This explains why water stops getting hotter when it reaches the boiling point: the power being pumped into the water by your stove begins going into potential energy rather than kinetic energy.
As shown in the figure above, every stored form of energy that we encounter in everyday life turns out to be a form of potential energy at the atomic level. The forces between atoms are electrical and magnetic in nature, so these are actually electrical and magnetic potential energies.
Even if we wish to include nuclear reactions in the picture, there still turn out to be only four fundamental types of energy:
Astute students often ask me how light fits into this picture. This is a very good question, and in fact it could be argued that it is the basic question that led to Einstein's theory of relativity as well as the modern quantum picture of nature. Since these are topics for books 4, 5, and 6 of this series, we will have to be content with half an answer at this point. Essentially we may think of light energy as a form of kinetic energy, but one for which kinetic energy is not given by (1/2)mv2 but rather by some other equation. (We know that (1/2)mv2 would not make sense, because light has no mass, and furthermore, high-energy beams of light do not differ in speed from low-energy ones.)
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Home Conservation Laws Simplifying the Energy Zoo All Energy is Potential or Kinetic |