Why Is Heat Known As Wasted Energy and Why is Everything Hot?

Everything is hot. That is, it contains some heat. And as a consequence, it has a temperature. Even an ice cube contains heat. “Hot” is strictly a relative term.

Heat is the ultimate form of energy, the form into which all other forms ultimately degenerate. There is energy of motion (Techspeak: kinetic energy), there is gravitational energy, chemical energy and electrical energy. They can all be converted into one another with the right equipment. We can convert gravitational energy into kinetic energy by pushing a boulder off a cliff. We can convert a waterfall’s kinetic energy into electrical energy by connecting a waterwheel to a generator. We can convert chemical energy into electrical energy with a battery, and so on.

But no conversion can be 100 percent complete. Some of the energy must inevitably be “wasted”, turned into heat. When the boulder hits the ground it heats it up a bit and we lose that amount of heat energy. When the waterwheel turns, its bearings get warm from friction and we lose that amount of heat energy. When a battery delivers current it gets hot from the chemical reactions inside and we lose that amount of heat energy. In short, we can convert and reconvert energy as much as we like, but each time, we will lose a little in the form of heat.

Can we collect that “wasted” heat and convert it back into another form? After all, we seem to be recycling everything these days; can’t we recycle heat energy? Sure, but not completely. That’s because heat is a chaotic motion of atoms and molecules , and to restore them to order takes work: energy. We must spend energy to recover that heat energy, so the bottom line on the energy balance sheet will always show a net deficit.

The preceding ideas are embodied in what is known as the Second Law of Thermodynamics, which is one of the most profound sets of realizations ever to dawn upon the mind of man.But although we can’t use it with 100 percent efficiency, heat is far from a minor player in the energy game. The world thrives on heat. It is the common currency, the euro of energy, if you will, that we humans manipulate to suit our energetic objectives. We add it to our ovens and we remove it from our refrigerators, after first converting it into electricity, of course, which is so much easier to handle than fire.

Like unfettered physical objects, heat can travel from one place to another as long as it is going “downhill”: from someplace at a higher temperature to someplace at a lower one. In that sense, flowing heat is very much like flowing water.

But does the heat flow because the higher-temperature object contains more heat than the lower-temperature object? Not necessarily. People often confuse heat with temperature, people who haven’t read this chapter, that is.

Using water flow as an analogy to heat flow, try this riddle on for size. Then return to it after you’ve read the section that begins on page 79.

If a waterfall flows spontaneously down from lake A into lake B, does that mean that there is more water in lake A than in lake B? (Note: Heat is analogous to the amount of water, while temperature is analogous to the altitude.)

This post is about heat and the electricity that we make out of it. It’s about global cooling (yes, cooling), cold feet, cold steel, hot fire, sparrows, refrigerators, thermometers and bathtubs.

Who is this guy Lewis Carroll, with his shoes, ships and sealing wax?