Karen Hill

Those ladders of fuzzy black dashes used as evidence in court are just a way of making DNA visible to jurors and other ardent scholars of biochemical science certain things that are too small to see, even with a microscope. They’re the end result of a number of laboratory manipulations that never get explained in … Read more

Everything is made of particles: atoms and molecules. But it’s not simply that some particles are lighter than others, although that’s a big part of it. It’s also that some particles are packed more tightly together than others. Lead is denser than, i.e., heavier than the same volume of, water, mostly because lead atoms are … Read more

Yes, there is a much simpler way, and it’s a shame they don’t teach it in school. Once those complicated formulas with all their parentheses and 32s got into a textbook somewhere, they seem to have taken on a life of their own. Here’s the simple method: To convert a Celsius temperature to Fahrenheit, just … Read more

Among all the nations of the world, only four great powers, Brunei, Myanmar (Burma), Yemen, and the United States of America, have not yet adopted the metric system of measurement. Is it possible that the rest of the world is onto something that has thus far eluded these four? Let’s see how our creaky and … Read more

Suppose that the Rockettes came on stage one at a time and did solos. You would agree that the intended effect would be lost, would you not? But that’s exactly how school science curricula are designed: the chemistry and physics teachers do solo acts on separate stages, and there’s no course in school called Putting … Read more

Pedestrians in the vicinity of Chicago’s 1454-foot Sears Tower need not fear. Hatted or not, they are in little danger from purely scientific experiments such as yours. (We won’t deign to discuss water balloons.) What you undoubtedly have in mind is the acceleration due to gravity, the fact that a falling object will fall faster … Read more

Magnets are attracted only to other magnets. A piece of iron contains billions of tiny magnets, but copper and aluminum don’t. The only thing that the pole of a magnet will attract is the opposite pole of another magnet. It’s exactly the same as with electric charges: The only thing that a positive electric charge … Read more

All atomic nuclei are made up of particles called nucleons. A big nucleus like uranium’s is a conglomeration of more than a couple of hundred of these particles, all crowded together into an incredibly tiny space. That’s such a large number of objects to hold together that the nucleus’s average grip on each one is … Read more

Uranium doesn’t burn like in a combustion, a chemical reaction with the oxygen in the air. But the uranium atoms do get used up. Coal, oil, and uranium contain energy. Actually, every substance contains a certain amount of energy. It is inherent in the unique arrangement of its atoms and how they are held together. … Read more

Frankly, E = mc2 doesn’t mean a hell of a lot. But that’s not to say that it isn’t one of the most momentous realizations ever to dawn upon the human mind. Although it has to do with things that are happening right under our noses every day, they are much too small to notice except … Read more

Twenty degrees, eh? Well, let’s just see about that. (We’ll assume that we’re dealing with Fahrenheit cucumbers, rather than Celsius.) If cucumbers are always twenty degrees cooler than their surroundings, let’s put a cucumber into a barrel with a whole bunch of other cucumbers and wait to see what happens. Will they fight it out, … Read more

Superman could probably see through lead with his X-ray vision if he really tried. It’s just that his inventors, Jerry Siegel and Joe Shuster, told him that he can see through anything but lead, and like any good cartoon character, he faithfully obeys his creators. Siegel and Shuster’s idea seems to have been that X-rays … Read more

Strictly speaking, infrared radiation is neither light nor heat. It’s not light because we can’t see it, and it’s not heat because it contains no substance that is capable of being hot. I like to call it “heat in transit.” We’ll see why. Infrared radiation is nothing more than a certain segment of the broad … Read more

If you listen with a linguist’s ear, you’ll find that the ice in your drink isn’t actually popping, which implies a certain hollowness. But it certainly does snap and, on occasion, crackle. First, the snap. When you plunge a cold ice cube into a warmer liquid, the water warms up parts of the ice cube, … Read more

As we were saying, water is a champion heat absorber, without getting very hot in the process. When you put a flame; to something that’s wet, the water soaks up the heat like a sponge, preventing the object itself from ever getting hot! enough to ignite. This one will astound you. Put a little water … Read more

Before we get any further, note well: Water must never be used on an electrical fire or on an oil or grease fire. Reasons: Water conducts electricity and can lead it elsewhere, perhaps to your very own feet. And because water won’t mix with oil or grease, it just scrambles it around and spreads the … Read more

Solid ice itself isn’t slippery. There’s a thin film of liquid water on its surface that the skaters are sliding on. Solids in general aren’t slippery because their surface molecules are tied tightly together and can’t roll around like ball bearings. The molecules of liquids, on the other hand, are free to move around, so … Read more

As we delve into how the boiling temperature of water depends on the weather, uncover the fascinating dynamics that influence how and when water boils, providing a nuanced understanding of this common yet intricate phenomenon. The weather has only a small effect on the boiling temperature of water. When people go around saying that water … Read more

When it’s boiling, water in New York is a little hotter than water in Mexico City. And hotter water will get an egg to a given state of doneness in a shorter time. A little thought will show that the biggest difference between New York and Mexico City, apart from the relative difficulty of finding … Read more

“Water seeks its own level” is a catch phrase that was probably uttered by a Greek philosopher two thousand years ago, and people have been parroting it ever since. In plain language, it means that water will lie flat whenever it can. If a body of water, anywhere from a bucket to a bathtub to … Read more

Generally, yes. But water is an exception. As trivial as this question may sound, the answer is of life-and-death importance. If ice didn’t float on water, we might not even be here to wonder why. Let’s see what would happen if ice sank in liquid water. In prehistoric times, whenever the weather got cold enough … Read more

This controversy has been raging ever since the early seventeenth century, when Sir Francis Bacon became a charter member of the Betcha-the-hot-water-freezes-first camp. The only appropriate answer to this puzzle is, “It depends.” It depends on precisely how the freezing is being carried out. Freezing water may sound like the simplest of happenings, but there … Read more

No, all liquids are not wet. Even water is not always wet. It depends on who or what is the “wet-ee.” Make this inquiry of a linguist, however, and you’ll be told that it is a foolish question. The word wet is so intimately related to the word water in the roots of our language … Read more

In the strength of its inward-directed surface-tension force, water is the champion of all liquids. Its surface tension is so strong that water resists being stretched outward at all, even into the three-dimensional shape of smallest surface area: a sphere. Water knows that it can have an even smaller amount of surface area by simply … Read more

Let’s put it this way: You’d be pretty surprised if they were square, wouldn’t you? That’s because all of our experience since we were babies tells us that Mother Nature prefers smoothness. There just aren’t many natural objects that have! sharp points or jangling angles. The major exception is certain mineral crystals, which occur in … Read more

Fortunately, it isn’t necessary to answer that question, because divers, and fish,  don’t get the bends (more accurately known as decompression sickness) from staying down too long. Divers get the bends by coming up too fast, but fish can indeed get the bends from other causes. When the water pressure on a diver’s body is … Read more

Of course, it can always swish its tail and swim to wherever it wants to go, but that’s just a temporary solution. What it would really like to do is adapt its body to the pressure of the new depth, so that it can maintain its neutral buoyancy and rest there without constantly having to … Read more

In order to be at home suspended in seawater, in precisely neutral buoyancy without sinking or rising, a fish, or any other object, must have exactly the same overall density as the water. That is, it must weigh exactly the same as an equal volume of seawater. If it weighs more, it will sink to … Read more

If you doubt that the water exerts an upward pressure, try to submerge a balloon in the bathtub. You’ll feel a substantial upward push that resists your downward push. When we lowered the Admiral Nimitz into our giant bathtub, the water level rose; it got deeper. As every diver knows, deeper water means higher pressure. … Read more

Very simply. They change their amount of internal air space, thereby changing their density. You want to dive? You let water into your ballast tanks. You want to surface? You blow the water out with compressed air. It gets a bit tricky in reality, though, because the density of seawater actually varies a bit, depending … Read more

The pat answer to the everyday puzzle of why things float invariably goes like this: “According to Archimedes’ principle, a body immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced. And that’s why things float.” Perfectly correct, of course, but just about as illuminating as a … Read more

The answer is, “It does and it doesn’t.” Maybe that’s why people go around simply parroting the prefabricated, though hardly enlightening, answer, that “evaporation is a cooling process.” We notice that our sweat glands are exuding a liquid water containing a little salt and urea, onto our skin only at certain times, such as (a) … Read more

The cooling effect on your skin has little to do with the evaporation of perspiration, in case that’s what you were thinking. That effect peters out as soon as there is enough wind so that all the perspiration has already evaporated. A strong wind cools us because the moving stream of air molecules carries off … Read more

No, that would knock the sponsor’s neon signs off the sides, and that would never do because today’s blimps are nothing but flying billboards. Instead, they use a clever system of swapping helium and air back and forth. The blimp is, as you’ve noted, essentially a big rubber bag full of helium. The contraption floats … Read more

Antigravity? We don’t use that word. Science fiction is two shelves over to the left. Surprisingly, there is no upward-pushing force. It’s just that there is less downward-pulling force on the helium than there is on the air that surrounds it because helium gas is lighter than an equal volume of air. Gravity pulls less … Read more

The colors are actually glowing atoms, stimulated by electricity. It’s pretty much the same as making the colors in fireworks: Stimulate atoms with energy, and they’ll quickly get rid of the excess energy by emitting light of their own characteristic colors. There are a couple of differences (fortunately) between fireworks and neon signs. In neon … Read more

They add chemicals to the explosive mixtures that emit specific colors of light when subjected to heat. You could throw some of these same chemicals into your fireplace if you thought that a green fire, for example, might be more romantic. When you throw an atom into a fire, it can pick up some of … Read more

It’s a nice idea, because snowflakes certainly do have beautifully complex shapes, with spikes, lacy edges, and all the rest. But interlocking hooks and loops are a bit too much to expect. Besides, they’re much too fragile and brittle; when you pack them together they suffer a crushing experience. The answer lies in the fact … Read more

Just pumping a spray of water into the air wouldn’t work very well, except perhaps in extremely cold weather. And by the way, the machines don’t produce actual snowflakes; they make tiny beads of ice, each one around ten thousandths of an inch in diameter. The simple spraying of water wouldn’t work because when water … Read more

It really does get warmer when the snow begins to fall. Think of it this way: In order to melt a lot of ice or snow, you have to add heat to it. So when a lot of water freezes into ice or snow, which is the reverse process, that same amount of heat has … Read more

Freeze dried coffee is made by the sublimation of ice. Freeze-dried coffee differs from ordinary instant coffee in an important way. To make either kind of fast-beverage powder, they first brew two-thousand-pound batches of incredibly strong coffee. If they are making instant coffee, they then quick-dry this thick brew by dropping it down through a … Read more

The snow in winter isn’t melting if it’s below freezing; it is actually going straight off into the air as water vapor, without having to melt into liquid water first. We might be tempted to say that the snow is evaporating, but scientists prefer to reserve the word “evaporation” for liquids only. So when a … Read more

The Greenhouse Effect is the effect of infrared radiation-trapping by the Earth’s atmosphere, which can raise the average temperature at the surface of the entire globe, just as the trapping of infrared radiation within a greenhouse raises the temperature inside. The overall temperature of the Earth’s surface, averaged over all seasons and climates, depends on … Read more

Greenhouses, sometimes called hothouses or glasshouses, are always naturally warmer, without any artificial heating. But believe it or not, the main reason is not what everybody refers to as “the greenhouse effect.” A greenhouse is just a closed, glass container for plants. The glass lets in sunlight, which the plants need for growth, while keeping … Read more

You can tell the temperature by counting the chirps crickets make. All cold-blooded animals perform their functions faster at higher temperatures. Just compare how fast the ants run around in cool and hot weather. Crickets are no exception. They chirp at a rate that is geared directly to the temperature. To understand their message, all … Read more

It’s all a matter of how big the water droplets are. That’s what clouds are: collections of tiny droplets of water. The droplets are so small that under the continual bombardment of air molecules they are kept suspended in the air and do not settle out by gravity, until it rains, of course. The droplets … Read more

First of all, please don’t call air pressure “barometric pressure.” The air around us has a temperature that is measured by a thermometer, a humidity that is measured by a hygrometer, and a pressure that is measured by a barometer. Television weather reporters wouldn’t dream of talking about the air’s “thermometric temperature” or its “hygroscopic … Read more

It’s very simple. The molecules in air are so far apart that we’re actually looking through empty space. To notice anything at all, we would have to be able to see the individual molecules, but air molecules are about a thousand times smaller than anything we can observe, even with a microscope. We’re talking about … Read more

Those copper roofs on old churches and city halls have been out in the weather longer than a borrowed lawn mower, all those years that have passed since people could afford to cover roofs with that durable and beautiful red metal. Today copper is too expensive to use to shelter even the heads of politicians … Read more

While the temperature “in the shade” is a fairly reproducible figure, the temperature “in the sun” depends too much on whose temperature you’re talking about. Different objects, including different people in differed clothing, will experience different temperatures in the sun because they will absorb different amounts of different portions of the sunlight’s spectrum. Light-colored clothing, … Read more

Right on. When it is winter on the part of the Earth where you live (northern or southern hemisphere), your hemisphere is leaning away from the sun a bit. That is, the axis of the Earth wobbles, so that during winter in the northern hemisphere the North Pole is farther from the sun than the … Read more

The ninety-three-million-mile separation between the sun and the Earth pays little attention to our lunchtime or recreational schedule. The sun is essentially the same distance from your rapidly reddening nose at all times of day. But the strength of the sunshine varies, for two reasons: one atmospheric and one geometric. Picture the Earth as a … Read more

Waves can tell when they’re approaching a shore and actually turn to line up with it. What makes waves, of course, is wind blowing across the water’s surface. But it can’t be that the wind is always blowing the waves straight in to shore. Out in the ocean, the wind may be blowing every which … Read more

“Sea Breeze” isn’t just the name of a thousand beach motels. The breeze coming in from the sea is a real phenomenon that makes the shore cooler than it is inland at least in the afternoon, which is when people most want to cool off anyway. In the daytime, cool breezes almost invariably blow in … Read more

The term proof was coined in the seventeenth century when people proved, or tested, the alcohol content of whiskey by moistening gunpowder with it and setting it afire. (Honest.) A slow, even burn indicated the desired 50-percent-or-so of alcohol. If the booze was watered down, the flame would sputter. Today in the United States, 50 … Read more

Silly-sounding question, maybe, but with several interesting answers. People tend to put up with fishy smelling fish in markets and restaurants because they’re thinking, Well, what else should it smell like? But fish needn’t smell like fish at all. Not if it’s perfectly fresh. When they’re only a couple of hours removed from the water, … Read more

Jell-O and similar desserts are about 87 percent sugar and 9 or 10 percent gelatin, plus flavoring and coloring. Kids love three things about the stuff: It is brightly colored, it is very sweet, and it jiggles. Mothers don’t mind, because gelatin is pure protein. The gelatin, which of course is the jiggler, really does … Read more

When the liquid carbon dioxide in the tank turns into gaseous carbon dioxide, it gets cold enough to freeze some of the carbon dioxide into “snow.” But why, indeed? All that’s happening is that the compressed carbon dioxide gas is expanding as we let it loose into the room. Do expanding gases automatically get cold? … Read more

The smoke from dry ice isn’t smoke; it’s fog. Although dry ice is pure carbon dioxide, the fog itself is not carbon dioxide, as some people think. Carbon dioxide gas is invisible. The cloud of fog surrounding the dry ice is pure water. It has been condensed out of the air’s natural humidity by the … Read more

Hydrogenation is, quite sensibly, the name of the process by which hydrogen is added to something. Hydrogen is the lightest of all known substances, but paradoxically, hydro-genating an oil makes it thicker and more solid. If we went all out with complete hydrogenation, the oil would become as solid as candle wax, which would make … Read more

The very best way to get ketchup out of the bottle, as was once memorably demonstrated by David Letterman, is to grasp the bottle firmly around the bottom and swing it round and round over your head, like a lariat. Of course, the ketchup will splatter all over the walls, but you asked only how … Read more

Just smile. Anyone who thinks steaks contain blood, well, they’re wrong. They’re not necessarily wrong in their preference for eating well-done steaks, although many would argue that such behavior should be declared a felony. Where they’re wrong is in calling your steak bloody. There’s practically no blood in it at all. Blood, you might politely … Read more

It does sound odd, but something is really going on here. What makes the MSG story hard to swallow is that the terminology is misleading: “Flavor enhancers” do not enhance the flavors of food in the sense of improving them; that is, they don’t make anything taste better. What they do is intensify, or magnify, … Read more

If Gertrude Stein had been a chemist, she might have said, “Calcium carbonate is calcium carbonate is calcium carbonate.” Sure, clams and oysters make their shells out of calcium carbonate. But chemically speaking, it doesn’t matter whether the calcium carbonate in the supplement bottle came from an oyster bed or a bed of limestone, which … Read more

Sure, freezer burn is an oxymoron, but not a bad one at that. Take a good look at that ancient pork chop you’ve been keeping in the freezer for an emergency. Doesn’t its parched and shriveled surface look as if it had been seared? Believe it or not, “seared” doesn’t only refer to heat; it … Read more

The cold pack contains ammonium nitrate crystals and a thin, breakable pouch of water. When the pack is squeezed, the water pouch breaks and, with a little shaking, the ammonium nitrate dissolves in the water. When any chemical dissolves in water, it may either absorb heat, get cold, or release heat, get hot. Ammonium nitrate … Read more

Tradition, namely the dietary laws for the Jewish holiday Passover, demands the absence of any leavening agents such as yeast, baking soda, or baking powder. So matzos are made of flour and water only. Between Passovers, the manufacturers can cheat a little and add other ingredients to vary the flavor. If you make dough by … Read more

You’ll be the first to admit, won’t you, that corn contains a lot of starch? Well, starch is the key to corn syrup. They convert cornstarch into sugar by the magic of chemistry. Take away the water from a kernel of corn and the remainder is about 82 percent carbohydrates, a classification of natural organic … Read more

Let’s not think of food energy as energy to be used only for exercising and running around. Our bodies utilize the energy we get from food not only to move, but to digest and metabolize the food itself, to repair the continuous day-today wear and tear on our cells, to build new growth, and to … Read more

The fog is exactly the same as any fog: a collection of tiny particles of liquid water that have been condensed out of the air by a cold temperature, but are too tiny to fall down like rain. They are kept suspended by being constantly bombarded by air molecules. They look white because they reflect … Read more

Those quick thaw defrosting trays are also good at taking money directly out of your wallet. What they are is a remarkable new high-tech, space-age miracle called a slab of metal. Of all types of materials, metals are the best conductors of heat. So if you put your frozen hamburger on a slab of metal, … Read more

At a truck stop, I watched a trailer-truck driver banging fiercely on the sides of his trailer with a baseball bat. When I asked him what he was doing, he explained, “My rig is a thousand pounds overweight. I’m hauling two thousand pounds of pigeons, and so I’ve got to keep half of them in … Read more

Carbon dioxide and carbon monoxide are both dangerous gases, but in very different ways. Small amounts of carbon dioxide are normally present in the atmosphere. It gets there from volcanoes, from the decomposition of plant and animal matter, from the burning of coal and petroleum, and from the opening of cans of beer, which, however, … Read more

And that is indeed what is happening back in the gas station’s compressed-air tank as you allow some of its stored-up compressed air to expand into the outer world. Why does expansion cool a gas? Well, if a collection of flying gas molecules is suddenly allowed to expand into a bigger space, the molecules have … Read more

It can’t be friction, because putting air into a car tire doesn’t heat it up. The answer is that when air (or any gas) is compressed,  when it is forced into a smaller space, it gets hot. When you use your hand pump, you’re compressing the air in the pump, but when you use the … Read more

It’s not just the pressure you’re fighting against; you also have to consider the volume. It takes many more strokes of the pump to add a “pound of air” to the car tire than to the bike tire. What people loosely call a “pound of air” is not an amount of air, like a pound … Read more

Oil is a good lubricant, obviously, because it’s so slippery. But what makes a substance slippery? All liquids are slippery to some degree. A wet floor or highway, wet with water, is a well-recognized hazard that keeps many lawyers in expensive clothing. But water isn’t much use as a lubricant in our engines and other … Read more

Ordinarily, water is the best mixer in the world, and I don’t mean just with Scotch. It mixes with, it associates intimately with, it even welcomes into its very bosom, that is, it dissolves, more substances than any other liquid. That’s why it is sometimes called the universal solvent. But there is one family of … Read more

Contrary to what everybody says, the ice on your driveway doesn’t melt, any more than sugar melts in coffee or tea. People often confuse melting with dissolving. (“I don’t need an umbrella; I won’t melt in the rain.”) But melting, as you have already noted, requires heat. You can certainly melt ice or sugar by … Read more

It was an extremely cold day, wasn’t it? Below zero Fahrenheit, perhaps? That was the problem. Sand won’t work when it is too cold. In order to improve traction, the sand grains must become partially embedded into the ice, making tiny bumps in what had been a smooth surface, in effect, making “sandpaper” out of … Read more

By interfering with water’s molecules, dissolved substances not only lower its freezing point, they also raise its boiling point by making it harder for the water molecules to fly off into the air. With ethylene glycol dissolved in it, your coolant water has to get to a higher temperature than usual before it will boil. … Read more

Strange as it may sound, it’s true. A fifty-fifty mixture of ethylene glycol and water won’t freeze until the temperature gets down to about 34 degrees below zero Fahrenheit (-37 degrees Celsius), while pure antifreeze will freeze at about 11 degrees above zero (-12 degrees Celsius). Let’s see what’s going on here. It happens that … Read more

Rusting takes place through a juxtaposition of iron and oxygen that actually constitutes a miniature electric battery, on the atomic scale. That is, the oxygen molecules are taking electrons away from the iron atoms, and that is exactly what goes on inside a battery: electrons being snatched from one substance by another. Anything that helps … Read more

Iron plus oxygen plus water equals rust. That’s it. When all three are present, rust will inevitably occur. But if any member of this unholy triumvirate is missing, there can be no rust. Fortunately for us living creatures, but unfortunately for our garden tools and automobiles, oxygen and water vapor are present everywhere in the … Read more

They play hard rock music while it’s being poured. Sorry. The strength of pre-stressed concrete doesn’t come from heat tempering, as in the case of windshield glass. Pre-stressed concrete is concrete containing steel cables that have been subjected to tension, that is, that have been stressed by pulling on them lengthwise, before the concrete hardens. … Read more

Preventing the scatter of fragments is relatively easy. The windshield is actually a sandwich, with glass “bread” and an elastic plastic “ham” that can be indented without cracking. When the bowling ball hits the windshield, most of the pieces of glass remain bonded to the plastic instead of flying around loose. But why it breaks … Read more

Don’t use flashlight batteries when they’re cold. They would be just as sluggish as a car battery in winter. Cold inhibits both kinds. They must be somewhere around room temperature if you are to get the intended amount of “juice” out of them. Batteries produce their electricity, streams of electrons, by a chemical reaction, and … Read more

Not unless the spinach was in a steel can, which is perversely known as a tin can, even when it’s an aluminum can. The much-touted iron in spinach just isn’t in a form that’s attractive to a magnet. Iron is magnetic, attracted to magnets, when it is in the metallic form, but not when it … Read more

There’s nothing unique about the use of sugar to preserve foods. In principle, you could make your strawberry jam with salt instead of sugar and it would keep just as long. Much longer, in fact, because nobody would go near it after the first taste. Salt has been used for thousands of years, however, to … Read more

Nonstick cooking sprays like Pam are nothing but cooking oil dissolved in alcohol, in a handy aerosol can. The idea is that instead of pouring a random amount of oil into your skillet, you give it a quick spritz from the can. The alcohol evaporates and the oil coats the pan. You’ll still be cooking … Read more