Science Matters by Robert M. Hazen Read Free Book Online

move, the greater the heat energy in the material of which they are part. This way of explaining the nature of heat says, in effect, that heat is simply a special kind of kinetic energy—the kind associated with atoms in motion.
    The recognition that heat is a form of energy was one of the great insights of nineteenth-century science, and is the foundation stone of thermodynamics. Although the notion seems simple to us (particularly when we picture heat as vigorously moving atoms), it is far from obvious that there is a connection between a pot of boiling water and a boulder perched on a hilltop.
Other Kinds of Energy
    When electrical current flows in a wire, electrons are moving. The kinetic energy of those electrons is one sort of electrical energy—one that lights your lamps, runs your stereo, and perhaps even cooks your food.
    Sound is a special kind of kinetic energy caused by regular patterns of atomic movement. We hear sounds because our ear drums vibrate in response to moving air molecules.
    Visible light carries with it energy that is related to electricity and magnetism. Other forms of radiation, such as radio waves and X-rays, carry the same kind of energy.
    In the twentieth century, a new category was added to the roster of known types of potential energy—mass. The equivalenceof mass and energy is embodied in science (and in folklore) by Einstein’s famous equation:
E = mc 2
. The equation says that mass can be converted into other forms of energy (and vice versa).
GOOD NEWS—THE FIRST LAW
    One of the most important features of energy is that it easily shifts from one form to another. When you ride a bicycle, chemical energy in your cells changes into the motion of your legs and, ultimately, into kinetic energy as the bike moves. When you climb a hill, some of your energy is converted to gravitational potential, and when you coast down the other side of the hill, that potential energy is converted back into kinetic energy as you speed up.
    No matter how often energy is converted from one form to another, there is one simple rule that always applies. The total energy—the sum of energy in all its forms—is the same after the conversion as it was before. Energy cannot be created or destroyed, only shifted from one type to another. We say that the total energy is “conserved,” and call this first law of thermodynamics the “conservation of energy.” Conservation of energy is one of the deepest and most widely applicable principles in the sciences, and operates everywhere from the largest supercluster of galaxies to the cells in your body to the smallest, most fundamental pieces of matter that we know about, the quarks. It is one of the great integrating principles of science.
    The first law of thermodynamics is the joy of amusement park owners and the bane of dieters. It tells us that the higher the roller coaster climbs, the faster we’ll go. It also tells us that the chemical energy or calories we take in as food must either beused to do work (exercise) or stored (as fat). The spate of new diet strategies that come out every year are a testimony to the power of the first law and to the futility of trying to avoid it.
    An easy way to picture the operation of the first law is to think about that roller coaster ride. You start at the bottom and powerful motors gradually pull the coaster up a steep incline to its highest point. During this phase of the ride electrical energy is converted to gravitational potential energy. At the top, gravity takes over and the car starts down. The car exchanges its gravitational potential for kinetic energy as it descends, moving faster and faster until it gets to the bottom. At this point in the ride, all of the original gravitational potential energy has been transformed to kinetic energy, and the car is moving as fast as it can go. As it starts back up the hill, it slows until it almost comes to rest at the next summit. And so it goes, potential and kinetic energy