What Einstein Told His Barber: More Scientific Answers to Everyday Questions - Robert L. Wolke (2000)
Chapter 3. Hot Stuff
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 chapter, then, 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?
I live in Miami and my twin sister lives in Tucson. One day on the telephone I mentioned that it was 80 degrees Fahrenheit (26 degrees Celsius) in Miami, and she jokingly said that it was “twice as hot” in Tucson. If that were really the case, what temperature would it be in Tucson?
It certainly wouldn't be 160 degrees Fahrenheit (71 degrees Celsius). But that's not because 160 degrees is too hot; it's not hot enough. The temperature that is “twice as hot” as 80 degrees Fahrenheit, believe it or not, is 621 degrees Fahrenheit!
Here's what's going on.
First of all, we must realize that heat and temperature are two different things. Please repeat after me: Heat is energy, while temperature is just our human way of telling one another how densely concentrated that heat is in an object.
Let's take heat first.
The amount of heat energy an object contains can be counted up in calories, just as if it were a donut. (A calorie is just an amount of energy, right?) But you'll grant that a big donut contains more calories than a small donut, won't you? Well, it's the same with the energy content of any substance. A quart (a liter) of boiling water contains twice as much heat energy as a pint (half a liter) of boiling water, even though they're both at the same 212-degree temperature.
Another example: There's a lot more heat in a bathtub full of warm water than in a single glassful that you might scoop out of that same bathtub, simply because there are more hot molecules in the tub. In short, the more of a substance you have, the more heat energy it contains.
(Right here, you may wish to take time out to take a crack at the riddle. The answer can be found at the end of this section.)
So your sister's problem, whether she realized it or not, was to figure out how much heat there actually was in the outside air—let's say a cubic yard (or a cubic meter) of it. Then if there was twice as much heat per cubic yard (or cubic meter) in the outside air as in your Miami air, she could really say it was “twice as hot.”
How can we determine the amount of heat in an object? Taking its temperature won't do the job, because that doesn't account for how big the object is. As we discovered in the bathtub, a big object containing lots of heat can be at the same temperature as a smaller object containing much less heat. Moreover, temperatures, whether expressed as Fahrenheit or Celsius, are nothing but arbitrary numbers invented by those two eponymous gentlemen. They're merely convenient labels for people to talk about—numbers that everyone has agreed to, as if proclaimed on Mount Sinai: “Whensoever thine ice melteth, it shall be called 32 degrees Fahrenheit or zero degrees Celsius. And whensoever thy water boileth, it shall be called 212 degrees Fahrenheit or 100 degrees Celsius.” These proclamations were made not by the Lord, but by Messrs. Fahrenheit and Celsius.
But the amount of heat that an object contains cannot be subject to humans' monkeying around with numbers. We need an absolute way of expressing the heat content of things.
The crux of the problem is that on either of our temperature scales, zero temperature does not mean zero content of heat. Zero degrees Celsius, for example, is merely the temperature of melting ice. Does that mean that there can be nothing colder than melting ice? Of course not.
Or look at it this way: How can you use a scale to measure something if its zero doesn't really mean zero? Picture a yardstick (or meter stick) with “zero inches” (or “zero centimeters”) somewhere in the middle, instead of at the left end. Just think of the crazy measurements you'd get.
So if we're ever going to be able to measure the amount of heat in an object, or in the air for that matter, we'll have to have a scale of numbers on which zero actually means no heat at all. And that's where the Lord really does come in. No, not that Lord. Lord Kelvin, a British nobleman and scientist (1824–1907), whose street moniker was William Thomson.
Kelvin set up a scale of temperatures that begins at “no heat at all”—a temperature of absolutely zero, where things are as cold as they can possibly get: “absolute zero.” Then, he borrowed the size of Mr. Celsius's degree and started counting upward from there. When you do that, the temperature of freezing water, zero degrees Celsius, turns out to be 273 degrees above absolute zero, and the temperature of boiling water—100 degrees Celsius—is 373 degrees above absolute zero. Human body temperature (37 degrees Celsius) turns out to be 310 degrees on the absolute scale. (Tell that to your doctor when he asks what your temperature is.) You can see that the absolute temperature, measured in Kelvins in honor of Lord Kelvin, is the Celsius temperature plus 273.
Now we're ready to answer your sister's riddle. If Tucson air contains twice as much heat per cubic yard (or per cubic meter) as Miami air, then what we must double is the absolute temperature of the Miami air. First converting your 80-degree Fahrenheit temperature into Celsius (for how to do that), we get 27 degrees Celsius. Adding 273 gives us 300 Kelvins, which is now a real measure of the heat content of the air. Doubling it to get twice the heat, we get 600 Kelvins, which converts to 327 Celsius or 621 degrees Fahrenheit as your sister's offhand estimate of the Tucson temperature! Yeah, we know, Sis: You don't feel it because the humidity is so low, right?
Similarly, inside your house, if your thermostat is set on 70 degrees Fahrenheit and you want twice the heat, you'd have to turn it up to 599 degrees Fahrenheit. You can take my word for that or do the calculation yourself. In a Celsius country, you'd have to turn the thermostat up to 313 degrees in order to make a 20-degree house twice as hot.
If your room's temperature is 70 degrees Fahrenheit and you want it to be twice as hot, you'd have to turn your thermostat up to about 600 degrees Fahrenheit.
To win this bet, there's no need to scribble calculations on a napkin. Just point out politely to your buddies as you pick up the money that the Fahrenheit scale doesn't read zero when there's a complete lack of heat; there's an awful lot of unaccounted-for heat below zero. Thus, the number “70” doesn't account for all the heat, and doubling it won't get you anywhere near twice the amount of heat.
You Didn't Ask, but …
Why is there a limit to how cold anything can get?
Heat is energy.
What kind of energy?
It's not electrical energy or nuclear energy or the kind of energy that your car has as you barrel down the highway. It's the energy that an object contains within itself, because the particles that it's made of, its atoms and molecules, are actually vibrating and bouncing around within their limited spaces like a bunch of maniacs in padded cells. The more vigorously those particles are moving, the hotter we say the stuff is: the higher its temperature. Even at the same temperature, though, a bigger chunk of the stuff will contain more heat energy because it contains more moving particles.
When we cool something down by taking heat energy out of it, the energy is lost by those moving particles, which will then be moving more slowly. Ultimately, if we cool it down far enough, we should reach a point where the particles stop moving altogether. We will have reached the lowest possible temperature: absolute zero.
And by the way, when you want to tell your doctor that you have no fever, please don't say that you have “no temperature.” That would mean that your body is at absolute zero, in which case a doctor would be of no help whatsoever.
Atomic and molecular motion don't stop dead-still at absolute zero. Theory says that there would be a tiny bit of residual energy left. But absolute zero isn't based on molecular motion anyway. It's the temperature at which a gas would shrink so much from the cold that it would disappear entirely. Nobody has yet succeeded in cooling a substance down to precisely absolute zero—in fact, theory says that it can never actually be reached—although experiments have gotten to within several billionths of a degree of it. For one thing, you'd have to keep a substance inside an absolute insulator, through which not a single atom's worth of heat can penetrate. And that's not exactly a job for a Kmart thermos bottle.
Answer to the riddle: Of course the waterfall doesn't care how big the lakes are. But just as water will flow from a higher altitude to a lower one no matter how much water is involved, heat will flow from a body at a higher temperature to a body at a lower one, no matter how big or small the bodies may be or how much actual heat they therefore contain. It's the temperature difference that counts—the difference in energy between the fast, hot molecules and the slower, cooler ones that they collide with and transmit their energy to.
Why does the tile floor in my bathroom feel so cold on my bare feet?
Assuming that you haven't forgotten to pay your gas bill, it's because porcelain tile conducts heat better than that cozy bath mat does, even though they're at the same temperature.
It's a common experience that certain things feel colder than others. People talk about “cold steel” as if the blade of a sword were somehow colder than its surroundings. Bakers like to roll out their pastry dough on a marble slab because “it's colder.” Just touch a steel knife blade or a marble slab and you'll have to agree: They do feel colder.
But they're not. The steel, the marble and the floor tiles aren't one bit colder than anything else in the room. They just feel as if they are.
If they have been in the same room for any reasonable amount of time, all objects will be at the same temperature as everything else in the room, because temperatures automatically even themselves out. Hot coffee cools off and cold beer warms up. Let a cup of hot coffee and a glass of cold beer stand side by side on the table long enough and they'll eventually come to the same temperature, the prevailing temperature of the room. (Nevertheless, you'll still think of the coffee as “cold” and the beer as “warm,” won't you?)
The reason is that heat spontaneously flows from warmer to cooler. That's because the molecules in a warm object are moving faster than the molecules in a cool object; that's what temperature is: a measure of the molecules' average speed. So when a warm object comes into contact with a cool one, its faster molecules will collide with the slower molecules and speed them up—that is, make them warmer.
If an object should happen to be initially colder than its surroundings, then heat will automatically flow into it until its temperature is the same as its surroundings. Or if an object happens to be initially warmer than its surroundings, heat will flow out of it into the surroundings. We have found it useful to think of heat flow as if it were flowing water. Water always flows to a lower level, while heat always flows to a lower temperature. We might even say that temperature seeks its own level.
It's not just steel, marble and tile that will feel cool to your touch. The temperature of your skin is a bit below 98.6 degrees Fahrenheit (37 degrees Celsius), while everything else in your room (except a hot radiator, perhaps) is at the room's prevailing temperature—around 70 degrees Fahrenheit (21 degrees Celsius). So when you touch an object in the room, it will feel cool to your skin because it really is cooler than your skin. Heat will therefore flow from your skin into the object, and your heat-deprived skin gives you the sensation of coolness.
Pick up various objects in the room you're in, other than obviously cool or warm objects such as a bottle of pop, a cup of coffee or the dog. Press them one by one against your forehead. They will all feel slightly cool to you.
But as you have discovered to your discomfort, some things do feel colder than others; the tile floor feels colder than the bath mat, even though we've seen that they must be at the same temperature. How come?
The answer is that, while all objects in the room are cooler than your skin and will therefore steal some heat from it, some materials are better heat thieves than others. Some materials are better heat conductors— they are better at carrying the stolen heat away. And the faster a material conducts the heat away, the cooler your skin is going to feel. It happens that porcelain tile is a much better heat conductor than the cotton or synthetic fiber bath mat is, so heat flows faster out of your tootsies when they're on the bare floor and they feel colder.
Different substances, being made of molecules with different properties—and that, of course, is why they are different substances—will transmit this heat with different degrees of speed and efficiency.
Substances made of big, unwieldy or rigidly fixed molecules won't be able to jostle their neighbors as easily, so they won't be able to transmit heat as quickly. That's the case with substances like cotton, wood and rubber, for example. Your wooden floor doesn't feel as cold as the tile floor, does it? That's because its big molecules can't steal heat away from your skin as fast.
Among all types of materials, gases are the worst conductors of heat. Their molecules are so far apart that they can barely find other molecules to bump up against. Almost everything conducts heat better than air, and that's why almost everything you touch feels cool to some extent; you're comparing it with the air that you're normally surrounded by and accustomed to. Air insulates you.
Metals, on the other hand, are the best conductors of heat among all materials, because of their unique structure. They contain loose electrons that can drift easily from one atom to another. That's why metals conduct electricity so well, but it's also why they conduct heat so well. Those tiny electrons can carry heat energy from one place to another much more efficiently than big, jostling atoms or molecules can, because they're so much more mobile. As the best thieves of heat from your skin, metals will feel coldest of all.
Engineers and physicists have measured how well many substances conduct heat (Techspeak: their thermal conductivities). Here, in round numbers, is how the thermal conductivities of some familiar materials stack up compared with air, to which I've assigned the number 1. The farther down the list you go, the colder the substance will feel when it's really at room temperature.
HOW VARIOUS MATERIALS CONDUCT HEAT, RELATIVE TO AIR
The moral of the story: Never build a house with silver bathroom floors. Or toilet seats.
Gabriel, You Blew it!
Why are the temperatures of freezing and boiling such odd numbers as 32 and 212 degrees Fahrenheit?
They are indeed strange numbers for such common, everyday goings-on as the freezing and boiling of water. We're stuck with them because a German glassblower and amateur physicist named Gabriel Fahrenheit (1686–1736) made a couple of bad decisions.
Gadgets for measuring temperature had existed since about 1592, even though nobody knew what temperature was, and nobody had tried to attach numbers to it.
Then in 1714 Fahrenheit constructed a glass tube containing a very thin thread of mercury—a nice, shiny, easily visible liquid—that went up and down by expansion and contraction as it got hotter and colder. But Fahrenheit's thermometer, like all that preceded it, was like a clock without a face. He had to put numbers on the thing, or else how could anyone complain about the weather?
So Fahrenheit had to devise a set of numbers to inscribe on his glass tubes, such that the mercury would rise to the same number on all thermometers when they were at the same temperature. And that's when Gabriel blew it. Historians still speculate about what must have been going through his mind, but the following might be a good guess.
First, he decided that because a full circle has 360 steps or degrees, it would be nice if there were also 360 steps—and why not call them degrees—between the temperatures of freezing water and boiling water. But 360 steps would make each degree too small, so he chose 180 instead.
That fixed the size of the degree: exactly 1/180th of the distance on the tube between the freezing and boiling marks. But what, he wondered, should the actual numbers be? Zero and 180? 180 and 360? Or, heaven forbid, 32 and 212? (212 ‒ 32 = 180, right?)
Well, he stuck his thermometer into the coldest concoction he could make—a mixture of ice and a chemical called ammonium chloride—and called that temperature “zero.” (What arrogance, Gabriel! Would nobody in human history ever be able to make a colder mixture? Why, two centuries later, we can make temperatures almost 460 degrees below your zero.)
When he took his own temperature, the thermometer went up to around 100 degrees. (Okay, 98.6, but see the following for how that number came about.) That was a touch that Fahrenheit liked: Humans, he felt, should score 100 on his temperature scale.
Next, he stuck his thermometer into an ice-water mixture, and found that the mercury went up 32 degrees higher than in his zero-temperature mixture. And that's how the freezing point of water came to be 32 degrees. Finally, if boiling water was to be 180 degrees higher than that, it would wind up at 32 + 180, or 212. End of Gabriel Fahrenheit's story.
Six years after Fahrenheit's body temperature became equal to that of his surroundings, a Swedish astronomer named Anders Celsius (1701–1744) proposed the centigrade scale of temperature, which we now call the Celsius scale. “Centigrade” means 100 degrees; he set the size of a degree so that there are 100 of them, not 180, between the freezing and boiling points of water. Furthermore, he defined his “zero temperature” at the freezing point of water, a reference point that anyone could easily reproduce. And thus, the boiling point of water fell at 100 degrees. (Curiously, for reasons known only to eighteenth-century Swedish astronomers, Celsius originally took the freezing point as 100 and the boiling point as zero, but people turned it around after he died.)
And what about that number 98.6 as the “normal” human body temperature? It's just a fluke. People's temperatures vary quite a bit depending on the time of day, the time of month (for women) and just plain differences in metabolism. But it wavers around an average of 37 degrees Celsius for most people, so that's what doctors have adopted as “normal.” And guess what 37 degrees Celsius converts to in Fahrenheit? Right—98.6, a number that looks for all the world as if it were more precise than it really is. That extra six-tenths of a degree is nothing but an accident of the conversion arithmetic and has no significance at all.
Speaking of conversions, I can't resist the opportunity—I do it every chance I get—to publicize an easy way to convert temperatures. I don't know why they continue to teach those complicated formulas in school, with all their 32s, parentheses and improper fractions, when there is a much simpler way that's absolutely accurate.
To convert Celsius to Fahrenheit, add 40, multiply by 1.8, then subtract 40.
To convert Fahrenheit to Celsius, add 40, divide by 1.8, then subtract 40.
That's all there is to it. It works because (a) 40 below zero is the same temperature on both scales and (b) a Celsius degree is 1.8 times larger than a Fahrenheit degree. (180 ÷ 100 = 1.8.)
A final point: Thermometers measure only their own temperatures.
Think about it. A cold thermometer registers a low temperature; a hot thermometer registers a high temperature. A thermometer doesn't register the temperature of an object that you stick it into until it itself warms up to, or cools down to, that object's temperature. That's why you have to wait for the fever thermometer to warm up to your body's temperature before you read it.
A fever thermometer doesn't measure your body's temperature; it measures its own temperature.
Hot, Hotter, Hottest?
If absolute zero is the lowest possible temperature, is there a hottest possible temperature?
Yes. But let's start off at merely warm and gradually turn up the heat.
Heat is the energy that a substance contains within itself, due to the fact that its atoms and molecules are moving. But temperature is a man-made concept, invented so that we can converse among ourselves about how much of that energy a substance has and actually assign numbers to it. When we say we are “raising the temperature” of an object, we are adding heat energy to its atoms and molecules and making them move faster. The ultimate limit to cooling and slowing them down has to be when they're not moving at all; that's absolute zero. Our current question, then, comes down to whether there is any limit to how fast those atoms and molecules can move.
But long before we reach any such speed limit, several things will happen. First, if the substance is a solid it will melt into a liquid. Then at a higher temperature the liquid will boil and become a vapor or gas—a condition in which the atoms or molecules are flitting around freely in all directions. As the temperature gets higher and higher, they flit faster and faster. For example, the nitrogen molecules in the air in your 350-degree-Fahrenheit (177-degree-Celsius) oven are flitting about at an average speed of 1,400 miles per hour (2,300 kilometers per hour).
If the substance is made of molecules (clusters of atoms glued together), the molecules will eventually be knocked to pieces—broken apart into smaller fragments or even into their individual atoms by the shattering forces of their violent collisions. In other words, every molecular compound will decompose at a high enough temperature.
Will the individual atoms themselves ever be broken apart? Yes, indeed. At a high enough temperature the atoms' electrons will be torn off, resulting in a seething, fluid inferno of free electrons and charged atomic fragments, called a plasma. This is the stuff of the interiors of stars, at temperatures in the tens of millions of degrees.
Still higher temperatures? Why not? There would seem to be nothing to prevent us from heating a plasma's electrons and atomic fragments to faster and faster speeds, except for one thing. There happens to be a speed limit in the universe: the speed of light in a vacuum, which is 671 million miles per hour (1.08 billion kilometers per hour).
Albert Einstein told us that the electrons in a plasma—or any object, for that matter—may approach the speed of light, but can never achieve it. He also told us that as a particle goes faster and faster, it gets heavier and heavier. For example, when cruising along at 99 percent of the speed of light, an electron has 7 times its normal mass; at 99.999 percent of the speed of light, it is 223 times heavier than when it's not moving.
There must be an ultimate temperature limit, then, lest the particles in a plasma reach the speed of light and become infinitely heavy. Theoretical considerations peg this temperature at around 140,000,000,000,000,000,000,000,000,000,000 degrees—Fahrenheit or Celsius, take your pick.
The next time someone says to you on a blazing summer day, “Whew! How hot can it get?” tell him.
But don't worry. Global warming still has a long way to go.
If Flames Always Go Upward, Why Do Buildings Burn Down?
How do flames always know which way is up?
Light a match and, while it's burning, twist it into a variety of positions. The flame keeps pointing unerringly upward, regardless of the orientation of its fuel. How, indeed, does it “know”?
You are well aware that hot air rises. (If you want to know why, check out p. 107.) A flame, whatever it is, must therefore be carried upward by the rising current of hot air. And that's all we need to know about why flames go upward.
But a more challenging question is, What is a flame? Is it the rising air itself, glowing from the heat? Nope.
A flame is a region of space in which a chemical reaction is going on: combustion— a reaction between the oxygen in the air and a flammable gas.
Did I say gas? Yes. But don't solids and liquids burn with flames also? Yes. (And when will I stop asking questions of myself?)
Wood and coal are solids, and they are indeed flammable; gasoline and kerosene are liquids, and they are indeed flammable. But none of them will actually burn until they have been converted into a gas or vapor. It's their vapors that burn, because only vapors can mix into the air intimately enough to rub elbows—rub molecules, that is—with the air's oxygen.
Molecules can't react unless they actually come into contact with one another. The oxygen gas in the air can't penetrate the solid or liquid fuel, so the fuel must vaporize and go out to meet the oxygen. That's why we have to light a fire. We have to get the fuel hot enough in at least one small location, so it will vaporize. Once the vapor starts burning, the heat of combustion—the combustion reaction releases heat—keeps vaporizing more and more fuel and keeps the process going until all the fuel is gone. (Provided that there is an inexhaustible supply of oxygen.)
A fuel that is already a vapor, such as the methane in our kitchen gas ranges, has no trouble mixing with the air, so it can be ignited by a mere spark. Propane-burning gas grills and butane-burning cigarette lighters contain those fuels in the liquid form, under pressure. But as soon as they are released, they vaporize into gases and mix into the air, whereupon they can also be ignited easily by a spark.
When we light a candle with a match, the match first has to melt a bit of the wax, the liquefied wax must travel up the wick by capillary attraction, and the match must vaporize some of that liquid. Only then can the wax vapor mix with the air and ignite. Without a wick to conduct the liquefied wax up to where there is a good air supply, a candle won't burn.
But if a flame is simply two invisible gases reacting with each other, how come we can see it? In the case of a candle, the flame is visible because oxygen can't flow in fast enough to react completely with all of the rapidly vaporizing wax. So some wax remains unburned as tiny particles of carbon, glowing yellow from the heat and swept upward by the current of hot air.
As the crowd of glowing carbon particles rises higher, the oxygen nibbles away at its outer edges, burning particles up completely into invisible carbon dioxide gas. The crowd of glowing particles is thus depleted more and more as it rises. That's why a candle flame tapers off toward its upper end.
Could we counteract global warming if everybody in the world turned on their air conditioners and refrigerators full blast and left the doors open?
Unfortunately, no, for several reasons.
First of all, the world's supply of air conditioners and refrigerators isn't anywhere near what you might think by looking around your neighborhood. But even if every citizen of the less-developed nations were privileged to enjoy cool bedrooms and frozen pizzas, the amount of available coolth wouldn't amount to an ice cube on a glacier. (Yes, I know there is no such word as coolth. Until now.)
Of course, you expected that answer, but maybe not this one: What you are proposing would actually heat up the world.
As you know too well from your electric bills, air-conditioning and refrigeration don't come free, in either money or energy. Someone has to produce the electricity that they use, and the production process itself gives off a lot of heat; it's part of the overall energy equation, and therefore part of the environmental problem.
In most cases, the first step in electricity production is to make heat through the burning of coal or by nuclear fission. Then the heat is used to boil water to make high-pressure steam, the steam is used to turn the blades of a turbine and the rotating turbine shaft drives an electricity generator.
That is a remarkably inefficient chain of events, and there's the rub. Or one of the rubs. Only about one-third of the fuel's inherent energy ever winds up as usable electricity. The other two-thirds goes up the smokestack as hot gases or down the river as hot cooling water, or else is lost while the electricity is being transmitted through the wires to your house, because power lines are slightly warmed by their resistance to the electricity flow. That's why birds perch there in cold weather.
More than anything else, then, what power plants really do is heat up the countryside. The more electricity you demand for cooling your food and brood, the more heat the power companies must fling into the environment. Instead of thinking about opening the door of your refrigerator, you'd be doing the world a favor by turning the appliance off!
Okay, you say, but all of that wasted heat is already part of the global warming picture. Turning our refrigerators and air conditioners loose upon the outdoors would have an effect over and above that, wouldn't it?
Again, unfortunately, no.
Consider how a refrigerator or air conditioner does its job. It takes in warm air, removes heat from it and discharges that heat somewhere else. The refrigerator removes heat from the air inside the box and throws it out into the kitchen via coils located behind or beneath the box, while the air conditioner takes in air from the room, extracts heat from it and throws it out the window. But—and here's the main reason your scheme won't work—these machines throw off even more heat than what they remove from the air. You might say that refrigerators and air conditioners make more heat than coolth. Here's why.
We know that the natural direction for heat to flow is “downhill” from a higher temperature to a lower one. In order to reverse that natural tendency and force heat to go “uphill” from a cool interior to a warmer exterior, the fridge or AC has to use electrical energy. (That's why you have to plug it in.) And that electrical energy, after it's done its job, turns into heat. You can feel it by touching the outside of the refrigerator or air conditioner; it's warm.
When you add it all up, then, there is more heat—usually about one-third more—coming out of the “cooling” machine than the amount it removed from the box or the room. The bottom line on the energy balance sheet tells us that these machines are actually heating devices.
The final nail in your cool-the-world coffin is this: Even if fridges and ACs could operate without using any electric power, the best you could hope for would be to break even: one calorie of heat discharged somewhere for every calorie removed from somewhere else. And that wouldn't change the world's overall quota of heat. All you'd be doing is moving it around.
Converting coal or nuclear energy into electricity is, as we've seen, a very inefficient process that puts a lot of waste heat into the environment. But what if your refrigerator and air conditioner ran on electricity from clean, non-fuel-burning sources such as hydroelectric (water), wind or solar power? While they certainly aren't as wasteful as the processes of burning coal and nuclear fuels, these energy sources still can't be converted to electricity with anywhere near 100 percent efficiency. And the waste energy inevitably shows up as environmental heat.
A refrigerator is really a heating machine.
How high does “high voltage” have to be before it's a serious hazard?
Voltage in itself isn't dangerous. A 10,000–volt shock can be no more disturbing than a pinprick, but you can get a serious jolt from a 12–volt automobile battery. What's dangerous is the amount of electric current that flows through your body as a result of the voltage.
A current of electricity, as you undoubtedly know, is a flow of electrons. The voltage is the amount of push that urges them to flow from one place to another. If they are given no place to flow to, no amount of urging by a voltage will make them flow. Voltage is like height: No matter how high you may be on a cliff, the height is harmless as long as you don't take a direct route to the ground below. Electrical safety is simply a matter of making sure that the electrons can get to the ground by a route other than through your body; they can't hurt you if they're not flowing through you. That's why the birds are safe perching on high-voltage transmission lines.
But it's high time we focused on those electrons that I talk about in several places throughout this book.
Electrons are the negatively charged particles that make up the entire bulk of all atoms. Every atom of every substance is essentially a blob of electrons with an incredibly tiny, incredibly heavy, positively charged nucleus buried somewhere in the middle.
The electrons in atoms have certain energies that are characteristic of the type of atom they're in. What makes a flow of electricity possible is that many of these electrons are easily detachable from the rest of their atoms and will travel elsewhere under the influence of a voltage shove. In most cases it takes only a few volts to evict at least some of them from their home atoms.
Some electrons are so loose that you can just rub them off. Scuff your shoes across a carpet on a dry day and some electrons will be rubbed off your shoes' atoms onto the carpet. Because your feet are presumably firmly connected to your shoes, your entire body now has a deficit of electrons, while the carpet has a surplus. Normally, all atoms are electrically neutral, because they have just as much positive charge in their nuclei as they have negative charge in their electrons. But now, your body has fewer electrons than your atoms require.
If you now touch an electron conductor such as a metal radiator or water pipe, electrons from the huge supply in the rest of the world—the ground—will eagerly leap to your finger even before it touches the metal, lighting up the intervening air with a crackling blue spark and inspiring you to utter an expletive. Instead of a water pipe you may even touch another person, who is unlikely to be as electron-deficient as you are, and some of his electrons will jump to your finger, eliciting an expletive from him.
But here's the thing: The voltage that urged the electrons to flow into your finger from the water pipe or your shocked friend may have been several thousand volts, but you're not dead because the number of flowing electrons—the amount of current—was much too small to do any harm to your body. After all, your shoe soles aren't exactly electric generators, like the ones down at the power plant that push gazillions of electrons through transmission lines to your house.
At home, where the voltage has been reduced to 120 or 240 volts, if you touch a “live” wire while some other part of you is connected to the ground, the power company will blindly supply as many electrons as can possibly flow through your body—that is, as large a current as can flow through you, given your body's resistance to the flow. And you're a dead duck.
In short, the danger of electricity lies not in how many volts you are subjected to, but in how much electric current flows through your body. The trouble is that we never know what the current can or will be in any given situation, so we must stay away from any voltage above battery levels at all times.
You Didn't Ask, but …
If it's the current, not the voltage, that can electrocute a person, how much current is necessary to “do the job”?
Electric current is measured in amperes. An ampere is a huge unit of electric current, equivalent to 6 billion billion (6 followed by 18 zeros) electrons passing by every second. So you often hear talk of milliamperes or milliamps— thousandths of amperes. One milliamp passing through your body will cause a mild tingling sensation. Ten to twenty milliamps can cause muscle spasms that may prevent you from letting go of the “hot” object. Two hundred milliamps, or two-tenths of an ampere, make the heart fibrillate (beat uncontrollably) and can be fatal. Larger currents can stop the heart entirely, but they may not always be lethal because the heart can sometimes be restarted to beat normally again.
A typical automobile battery is capable of delivering a hundred amperes or more; it takes that much current to do the job of turning over an engine. The only reason that auto mechanics aren't dropping like flies is their electrical resistance; every substance resists the flow of electricity to a certain degree, and the resistance of human bodies is quite high. That's why it takes a substantial voltage to force enough electrons through a person to electrocute him or her. A 12–volt auto battery doesn't have that much force.
We may encounter dangerous electricity in many different circumstances. I'll assume that you are not terribly concerned about being formally electrocuted while seated in a special chair. But what about lightning? The surge of electrons between a cloud and the ground, or between two clouds, is powered by tens of millions of volts, and that can force tens of thousands of milliamps through the air, which ordinarily won't conduct electricity at all. Get in the way, and a lot of those milliamps can go through you.
How do you “get in the way”? By being close to an object that is offering the lightning's current an easy path to the ground. If ever there were a situation in which the expression “path of least resistance” applies, this is it. The lightning's electrons will flow through the best conductors—materials having the least electrical resistance—that they can find. If you offer them an attractive detour through your body, they'll take it.
Of all materials, metals are the best conductors of electricity; they have the lowest electrical resistance. That's because the electrons in metal atoms are very loose and can flow right along as part of the current. So when sudden thunderstorms have come up on the greens, a bag of metal golf clubs has been many a duffer's ticket to that great fairway in the sky.
Because air is such a poor conductor of electricity, the lightning will take almost any other available path rather than plowing through the air for those last several yards to the ground. Trees, with their nice, juicy sap inside, offer lightning a preferred alternative, so taking shelter from a thunderstorm under a tree may also earn you a trip to the ultimate nineteenth hole. But even if you're out on the seventh green with no trees nearby when a storm comes up, little old you, sticking up only six feet off the ground, can be the lightning's preferred route. Your best lie, so to speak, is flat on the ground, away from your clubs and cart.
Why Doesn't It Rain Roasted Sparrows?
Why don't birds get electrocuted when perching on high-voltage power lines?
This question is as old as electric power itself. It has been asked almost as often as “Do you love me?” and with equally unconvincing replies.
The common answer—“The birds aren't electrocuted because they're not grounded”—doesn't get to the root of the question. Does everyone who walks away after that explanation really know what “grounded” means? What's so special about touching the ground?
As you know, an electric current is a flow of electrons. The key word here is “flow.” Unless the electrons can flow from one place to another, they can't do anything useful, or harmful, any more than a stream can turn a waterwheel by standing still. To get electric light, for example, we make electrons flow through a thin tungsten filament, in one end and out the other. In forcing their way through the very thin tungsten wire under the influence of a 115–volt push, they heat it so much that it glows white hot.
Notice that the voltage is the push; that's what voltage is: a force that pushes electrons from one place to another so they can do work for us. But no matter how high the voltage, the electrons can't do anything unless they are given a path to traverse. The power transmission wires are that path. Under the influence of a high-voltage push, they conduct electrons all the way from the power plant to our houses, where they may be tapped off to flow through a lightbulb, a toaster or a television set.
Where do the electrons go after they pass through our electric appliances? They return to Mother Earth, which is where the electric company got them from in the first place. Where else, for heaven's sake, could they have gotten them? The moon? So Mother Earth, whom we familiarly refer to as “the ground,” is the original source of electrons at the power company and their final destination when we're done making them work for us. Earth is made of gazillions of atoms containing multigazillions of electrons. By rough estimate, the number of electrons on Earth is 1, followed by 51 zeros. That's what I'd call an inexhaustible supply.
Now, back to the birds. Their little feet are certainly in contact with lots of electrons that are waiting to be drained off and returned to the ground via your electric toaster. But fortunately for the birds, their bodies offer no way of leading the electrons to the ground. The birds just aren't connected to anything; they're a blind alley, an electron dead end. The electrons thus have no way of using the birds as a conduit to the ground, and no electricity flows through them. That's why we don't experience a rain of electrocuted sparrows.
And by the way, what are those birds doing on the power lines in the first place, besides befouling your automobile? In the winter, at least, they are there because the electric current going through the wires generates a small amount of heat that keeps their tootsies warm. And while we're at it, how can they sleep there without falling off? When their foot muscles are relaxed, they tighten up, rather than loosen like ours do. So never fall asleep while hanging from a tree branch.
You may have seen an electric company lineman, raised from a truck in a “bucket,” working on electric wires with his bare hands. He's as safe as the birds, because the bucket is completely isolated—insulated—from the ground. Electrons can't find a path through the lineman's body to the ground, so they can't make him glow like a white-hot tungsten filament.