How Everything Works   Page 123 of 160 (1595 Questions and Answers) Printer Friendly Version

1221. Suppose that I fill a rigid container with water and that this container will not expand or contract as its temperature changes. Will the water turn to ice when I cool it below 0° C? — PL, Taikoo Shing, Hong Kong
Since water normally expands as it forms ice, the rigid container will prevent it from freezing at 0° C. If the container was completely filled with water at room temperature, then an "empty" region will appear inside the container when you first begin to cool it toward freezing. That's because water contracts as you cool it toward 4° C. The "empty" region isn't really empty, it contains gaseous water vapor. But once the water's temperature drops below 4° C, the water begins to expand as it cools. It will first expand into the "empty" region, but when that region becomes full the water will no longer be able to expand. Instead, its pressure will begin to rise dramatically. This elevated pressure is what will ultimately prevent the water from freezing at 0° C—high pressure depresses water's freezing temperature. Although the water will eventually freeze, you'll have to cool it far below 0° C for that to occur.

1222. When water boils the "air bubbles" rising from the bottom of the pan seem to be created spontaneously out of nothing. I told my son that they are not air bubbles but rather water vapor. Is that correct? — JG, Austin, TX
Yes, these bubbles contain water vapor, not air. The reason that you don't see them until the water reaches its boiling temperature is that a bubble containing only water vapor isn't stable at lower temperatures—the surrounding air pressure will crush it. But once the water temperature is high enough, the water vapor bubbles are stable and they grow while rising to the top of the water.

1223. What is the relative insulating value of various levels of vacuum? For example, how insulating is 1/2 atmosphere as compared to full atmosphere?
Amazingly enough, air's ability to carry heat doesn't change much as you reduce its pressure and density as long as you stay above about a thousandth of atmospheric pressure and density. That's because reducing the density of air molecules may leave fewer particles to carry heat, but it also allows them to travel farther before they collide with other molecules. The reduction in molecular density is almost perfectly cancelled by an increase in the mean free path those molecules travel between collisions—there are fewer heat carriers, but they can move more easily. It isn't until you reach very low pressures and densities—so that the mean free path begins to approach the size of the enclosed gas—that reducing the air pressure and density begins to decrease the air's ability to carry heat. That's why even a small leakage of gas into a vacuum flask spoils that flask's insulating characteristics. However, you can decrease the "air's" ability to carry heat by increasing the mass of its molecules—heavier particles such as carbon dioxide or krypton travel more slowly than normal air molecules and don't carry heat as well.

1224. How much current can a power generator produce and how does that current vary as you introduce more load onto the generator?
There is no fundamental limit to how much current a generator can handle, however, the characteristics of the generator's wiring, its magnetic fields, and the machinery turning it all tend to limit its current capacity. A generator's wires aren't perfect and, as the current passing through the generator increases, its wires waste more and more power. Like any wiring, a generator's wires convert electric power into thermal power in proportion to the square of the current. Thus if you double the current in the generator, you quadruple the power loss. While this power loss and the resulting heat are trivial at low currents, they become serious problems at high currents.

Increasing the current in the generator also affects its magnetic fields because currents are magnetic. At a low current, the current's magnetism can be ignored. But when a generator is handling a very large current, the magnetic fields associated with that current are no longer small perturbations on the generator's normal magnetic fields and the generator may not perform properly any more.

Finally, a generator's job is to transfer energy from a mechanical system to the electric current passing through it. As the amount of current in the generator increases, the amount of work that the mechanical system provides must also increase—the generator becomes harder to turn. There will always be a limit to how much torque an engine or crank can exert on the generator to keep it spinning and thus there will be a limit to how much current the generator can handle.

As for how the current varies with load: the more current the load permits to pass through it, the more current will pass through the generator. Assuming that the generator is well built and has very little electric resistance, the load will serve to limit the current. The generator will then deliver just as much current as the load will permit. If the load permits more current, the generator will deliver more. As a result, the wires in the generator will waste more power as heat, the magnetic fields in the generator will become more complicated, and the device powering the generator will have to work harder to keep the generator turning.

1225. Given a certain chemical structure, can it be determined which spectrum of light that molecule will absorb? Are there any known compounds that charge their color or intensity when exposed to electric fields? - GS
While it is possible in principle to calculate the exact spectrum of light that a molecule will absorb, in practice it is normally extremely difficult. It's a matter of complexity—the quantum mechanical equations describing a molecule's electromagnetic structure are easy to write down but extraordinarily difficult to solve, even in approximation. One of the great challenges of atomic and molecular physics and physical chemistry is determining the full quantum mechanical structure of atoms and molecules through calculation alone. Except with small atoms and molecules, it's awfully hard but not impossible. As computers get faster and approximation schemes get better, the calculated spectra of molecules get closer to their experimental values.

As for compounds that change their optical properties while in electric fields, the answer is yes—all compounds exhibit such changes, although they may be undetectably small. However, I can't think of any isolated molecules that change dramatically in normal fields. Still, electric fields can alter the "selection rules"—the symmetry-based laws that often control which optical transitions can or cannot occur. It's possible that a modest electric field will turn on or off import optical transitions in some molecules so that they exhibit large color changes in small fields. Still, I can't think of any useful examples.

1226. Why are metal-halide lamps so efficient?
Metal-halide lamps are actually high-pressure mercury lamps with small amounts of metal-halides added to improve the color balance. Light in such a lamp is created by an electric arc—electricity is passing through a gas in the lamp and causing violent collisions within the gas. These collisions transfer energy to the mercury and other gaseous atoms in the lamp and these atoms usually emit that energy as light. Overall, an electric current passes through the lamp and gives up most of its energy as light and heat in the gas. As you've noted, the lamp is relatively efficient, meaning that it produces more light and less heat than ordinary incandescent or halogen lamps. However, metal-halide lamps aren't quite as energy efficient as fluorescent lamps.

What makes a metal-halide lamp so efficient is that there are relatively few ways for the lamp to waste energy as heat. While collisionally excited mercury atoms normally emit most of their stored energy as ultraviolet light—the basis for fluorescent lamps—they can't do this in a high-pressure environment. A phenomenon called "radiation trapping" makes it almost impossible for this ultraviolet light to escape from a dense vapor of mercury, so a high-pressure mercury lamp emits mostly visible light. Even without the metal-halides, a high-pressure mercury lamp emits a brilliant blue-white glow. The metal-halides boost the reds and other colors in the lamp to make its light "warmer" and more like sunlight.

Next time you watch one of these lamps warm up, observe how its colors change. When it first starts up, its pressure is low and it emits mostly invisible ultraviolet light (which is absorbed by the lamp's glass envelope). But as the lamp heats up and its pressure increases, the rich, white light gradually develops. Incidentally, if the power to a hot lamp is interrupted, the lamp has to cool down before it can restart because it only starts well at low pressures.

1227. How does a projector work?
A projector is essentially a camera that's operating backward. When you take a picture of a tree, all of the light striking the camera lens from a particular leaf is bent together to one small spot on the film. Overall, light from each leaf is bent together to a corresponding spot on the film and a pattern of light that looks just like the tree—a real image of the tree—forms on the surface of the film. The film records this pattern of light through photochemical processes, and subsequent development causes the film to display this captured light pattern forever. Because of the nature of the bending process, the real image that forms on the film is upside-down and backward. Because it forms so near the camera lens, it's also much smaller than the tree itself.

A projector just reverses this process. Now light starts out from an illuminated piece of developed film—such as a slide containing an image of a tree. Now the projector lens bends all of the light striking it from a particular leaf spot on the slide together to one small spot on a distant projection screen. Again, light from each leaf on the slide is bent together to a corresponding spot on the screen and a pattern of light that looks just like the slide—a real image of the slide—forms on the surface of the projection screen. As before, this image is upside-down and backwards, which is why you must be careful how you orient a slide in a projector, lest you produce an inverted image on the screen.

1228. What do some permanent-magnet generators have stainless-steel axles? — RC, Port-au-Prince, Haiti
Many forms of stainless steel, including those designated as "18-8 stainless," are completely non-magnetic. In contrast to normal steel, which has a microscopic magnetic structure and is easily magnetized by a strong magnetic field, these non-magnetic stainless steels are entirely free of magnetic structure. They cannot be magnetized, even temporarily. In machinery that contains strong permanent magnets, using non-magnetic stainless steel for the mechanical parts avoids undesirable attractions between parts and distortions of the required magnetic fields. While copper, aluminum, or brass could also be used—they are non-magnetic as well—stainless steels are generally much tougher metals.

You have every reason to be skeptical about this sort of activity. Despite its length, I have included your entire question here because it gives me an opportunity to point out some of the differences between science and pseudo-science. You have written a wonderful survey of some of the quackery that exists in our society and have illustrated beautifully the widespread view that science is fundamentally nothing more than gibberish. I cringe as I read your review of "healing science" because in that description I see science, a field that has been developed with care by people I respect and admire, tossed cavalierly into the gutter by self-important know-nothings who aren't worth a moments notice. That these miserable individuals draw such attention, often at the expense of far more deserving real scientists—or worse, by "standing on the shoulders" of those real scientists—is a tragedy of modern society. It's just dreadful.

Let me begin to pick up the pieces by pointing out that terms like "human energy field", "vibrational medicine", and "energy imbalance" are simply meaningless and that the use of "Einstein's Theory" to justify healing-at-a-distance is typical of people who don't have a clue about what science actually is. The meaningless misuse of scientific terms and the uninformed and careless misapplication of scientific techniques is an activity called pseudo-science. Pseudo-science may sound and look like science, but the two have almost nothing else in common. Among the benefits of a good college education is learning how vast is the world of human knowledge, recognizing how little you know of that world, discovering how much others have already thought about everything you can imagine, and finding out how dangerous it is to venture unprepared into any area you do not know well. Most of these pseudo-scientific quacks are either oblivious of their own ignorance or so arrogant that they dismiss the work of others as not worthy of their attention. Either way, they make terrible students and, consequently, useless teachers. You'll do best to leave their books on the shelves.

Because real science is not buzzwords, simply stringing together the words of science does not make one a scientist. Science is an intense, self-reflective, skeptical, objective investigative process in which we try to form conceptual models for the universe and its contents, and try to test those models against the universe itself. We do this modeling and testing over and over again, improving and perfecting the models and discarding or modifying models that do not appear consistent with actual observations. Accurate models are valuable because they have predictive power—you can tell in advance how something will behave if you have modeled it correctly.

In the course of these scientific investigations, concepts arise which deserve names and so we assign names to them. In that manner, words such as "energy" and "vibration" have entered our language. Each such word has a very specific meaning and applies only in a specific context. Thus the word "force" was assigned to the concept we commonly refer to as a "push" or a "pull" and applies in the context of interactions between objects. The expression "the force be with you" has nothing to do with physics—the word "force" in that phrase doesn't mean a push or a pull and has nothing to do with the interactions between objects. As you can see, taken out of its applicable context and used carelessly in another usually renders a scientific word completely meaningless.

Alas, the average person doesn't understand science, doesn't speak its language, and cannot distinguish the correct use of the language of science from the meaningless gibberish of pseudo-science. As anyone who has spent time exploring the web ought to have discovered, highly polished prose and graphics is no guarantee of intelligent content. That's certainly true of what appears to be scientific material. I am further saddened to see that even the titles of academia are deemed fair game by the quacks. While the physics term "energy" and the biological word "medicine" can appear together in a sentence about cancer treatment or medical imaging, that's not what the person claiming to have a Ph.D. in "Energy Medicine" has in mind. That degree was probably granted by a group that understands neither physics nor medicine. There may be a place for non-traditional medicine because medicine is not an exact science—there is often more than one correct answer in medicine and there are poorly understood issues in medicine even at fairly basic levels.

However, physics is an exact science, with mechanical predictability (within the limitations of quantum mechanics) and only one truly correct answer to each question. Its self-consistent and quantitative nature leaves physics with no room for conflicting explanations. Like most academic physicists, I occasionally receive self-published books and manuscripts from people claiming to have discovered an entirely new physics that is far superior to the current one. And like most academic physicists, I flip briefly through these unreviewed documents and then, with a moment's sadness that the authors have wasted so much time, effort, and money, I toss them into the recycling bin. It's not that we scientists are close minded medieval keepers of the dogma, it's that these "new physics" offerings are the works of ignorant people who don't know what they don't know. Unlike real scientific revolutionaries like Galileo and Einstein, these people don't understand the strengths and weaknesses of the current scientific models. Their new offerings are usually inconsistent, fail to correctly model the real universe, add unnecessary complexity to simple phenomena, or all three. It's extraordinarily unlikely that anyone will ever successfully overthrow the basic laws of physics, not because no one will accept a new physics if it's actually correct but because the current physics already explains things with such incredible accuracy and predictive power. Developments in physics come almost exclusively at its frontier, where the current understanding of physics is known to be imperfect or incomplete, and that is probably where those developments will probably always occur.

So to return to your question, I would tell my students that I think that the "healing sciences" as you have identified them are neither.

1230. Why don't batteries work as well in cold environments? — KS
A battery uses electrochemical processes to provide power to a current passing it. This statement means that if you send an electric charge through the battery in the normal direction, that charge will emerge from the battery with more energy than it had when it entered the battery. But while it might seem that the number of electric charges passing through the battery each second doesn't matter—that each charge will pick up the usual amount of extra energy during its passage—that's not always the case. To understand this fact, let's look at how charges "pass through" the battery and how they pick up energy.

What's really happening is that electrochemical processes are spontaneously separating charges from one another inside the battery and placing those separated charges on the battery's terminals—the battery's negative terminal becomes negatively charged and its positive terminal becomes positively charged. This charge separating process proceeds in a random, statistical manner until enough charges accumulate on the terminals to prevent any further charge separation. Because like charges repel one another, sufficiently large accumulations of positive charges on the positive terminal and negative charges on the negative terminal stop further arrivals of those charges.

But when you send a positive charge through a wire and onto the battery's negative terminal, you reduce the amount of negative charge there and weaken the repulsive forces. As a result, the chemicals in the battery separate another pair of charges. The battery's negative terminal returns to normal, but now there is an extra positive charge on the battery's positive terminal. This extra charge flows away through a wire. Overall, it appears that your positive charge "passed through" the battery—entering the battery's negative terminal and emerging from the positive terminal with more energy than it had when it arrived at the negative terminal. But what really happened was that the battery's chemicals separated another pair of charges.

In a warm environment, the battery's chemicals can separate charges rapidly and can keep up with reasonably large currents of arriving charges. But in a cold battery, the electrochemical processes slow down and it becomes hard for the battery to keep up. If you try to send too much current through the battery while it's cold, it is unable to replace the charges on its terminals quickly enough and it voltage sags—it doesn't have enough separated charges on its terminals to give the charges "passing through" it their full increase in energy. If you use a battery while it's very cold, you should be careful not to send too much current through it because it will become inefficient and will provide less than its usual voltage.

www.HowEverythingWorks.org
The Complete Collection of Questions (160 pages, from oldest to newest):
 Previous 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 Next