Read Science Matters for Free Online Page B

dispersed as heat in the atmosphere, where it cannot be recovered to perform useful work. This limitation on how we can use energy is called the second law of thermodynamics.
    These two laws of thermodynamics govern all processes that involve heat and other forms of energy.
WORK, ENERGY, AND POWER
    Thermodynamics relies on three concepts: work, energy, and power. Each of these words has an everyday meaning, but scientists use them in slightly different, specialized ways.
    As far as physicists are concerned, work is done every time a force is used to move something. The amount of work done depends on how much force is used and how far the object moves (work equals force times distance). When you lift groceries, open a door, or throw a ball, you apply a force over a distance and move an object. You do work. The greater the force applied or the longer the distance moved, the more work is done. If you try to move something and fail (try to lift a car, for example, or push a wall) you haven’t done any work. You may have generated a force, but it was not applied over a distance. No matter how much effort you expend, if nothing moves, no work is done. Physicists can thus actually prove that bricklayers do more work than lawyers.
    Energy is the ability to do work—the ability to exert a force.
    Power is a measure of how quickly work is done: work done divided by the time it takes to do it. If you run up a flight of stairs instead of walking, you require more power, even though the total amount of work done is the same in both cases. In sports, the player who can generate power at the highest rates throws farther, hits harder, and runs faster.
TYPES OF ENERGY
    Energy comes in many forms. It can be converted from one form into another, but all the forms have one thing in common: they involve a system that is capable of exerting a force.
Potential Energy
    A boulder perched at the edge of a cliff has the potential to do work. If it is allowed to fall, it will exert a force as it creates a depression in the earth below. It must therefore possess energy while it’s sitting quietly at the top. We call this potential energy, where the term “potential” signifies that the system could do work, but isn’t doing so at the moment. Think of the boulder as storing energy against future use.
    If you dam a river, the water high in the reservoir has gravitational potential energy. We store this energy until we want to use it, at which time the water is allowed to fall and generate hydroelectric power. This is a common technique for generating electrical power, particularly in the northwestern United States.
    There are many different kinds of potential energy. Stretch a rubber band or compress a spring and they are ready to snap back, exerting a force over a distance as they do so. We say the rubber band has elastic potential energy. Coal, gasoline, and other combustibles store chemical potential energy, which is released to do work when they are burned. Energy can also be stored in magnets, in batteries, in the surface tension of drumheads and soap films, and in many other systems in nature.
Kinetic Energy
    Anything that moves possesses energy. A fastball headed toward home plate, a rotating waterwheel, a speeding car, or a falling leaf can do work. You see this any time a moving object stops. A moving baseball exerts a force on the catcher’s mitt, compressing the material and leaving an indentation. It exerts a force over the distance of the compression. A speeding car that stops suddenly (by hitting a tree, for example) exerts a force that makes the treemove. A rock slide or avalanche can obliterate an entire town. By virtue of the fact that it is moving, each of these objects can do work and therefore possesses kinetic energy.
    Every atom in a material is in motion, either moving freely (as in a gas) or vibrating (as in a solid). The kinetic energy of all these atoms is related to the phenomenon we call heat. The more vigorously atoms