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Q. Could pulling a perfectly taut rope with a bell at the end allow faster-than-light communication? —Leif K., 13, Vermont A. It sounds good. Yank the rope, the rope moves, the bell rings. Voilà! You've sent an instant message—and broken Albert Einstein's anoying law that nothing can travel faster than the speed of light. Right? Not quite. A rope, John Baez* told me, is actually a long chain of atoms. "Each atom in the rope must pull on the next one for the tug to move along, and this takes time," he said. Something similar, with pushing instead of pulling, happens when sound waves travel through a rope, so physicists weren't surprised to learn that a pull travels down a rope at the speed of sound. That's much slower than the speed of light, as you know if you've ever waited for thunder to arrive after a lightning flash. "So pushing or pulling something is a bad way to try to send signals faster than light," Dr. Baez said. —Robert *John Baez is a mathematical physicist at the University of California, Riverside. Andrew Hodges of the University of Oxford, United Kingdom, also answered the question. Q. Why is it that one tree will change into one kind of color scheme and pattern while another tree of the same species will change into a totally different pattern? —Kirsten Z., 14, Ohio A. Hey, I can answer this question because before I became a writer I was a plant scientist at the University of California, Berkeley. As you probably guessed, lots of things interact to give a tree's leaves their particular color patterns. The big ones are how much water the tree gets (is it in a swampy spot?), the temperature in its immediate locale (is it standing by the side of the road, exposed to cold winds?), and its health (a fungal infection, for instance, can make it break out in polka dots). Even trees of the same species standing right next to each oher can have totally different patterns. The leaves on one of two sweet gums down the street from me turn bright yellow, but the leaves on the other go straight to brown. —Rosanne Q. Why do people swing their arms back and forth when they run? —Anya, 7, Massachusetts A. It makes running a lot easier. Swinging your arms keeps your center of mass moving in a straight line when you run. The smoother the line, the less effort it takes to run. For kids, the center of mass is usually in the middle of your torso at just about the level of your bellybutton. (It's a little lower in most women and a little higher in most men.) It works this way: a step forward with your right leg pulls you a little to the right. But if you swing your left arm forward at the same time, it balances you. The same thing happens when you step forward with your left leg. Swing your right arm forward at the same time, and you stay on track. If you don't believe this, try running while one arm's still and the other's swinging normally. That's what professor Jessica Rose Agramonte* did after explaining to me why we swing. "It's an awkward way to run," she said. "The swinging arm seemed to rotate my body too far toward the other side. The still arm didn't counterbalance it." —Rosanne *Jessica Rose Agramonte, a professor at Stanford University Schol of Medicine, studies movement and walking. Q. Why do all the birds in a flock seem to move all at once? To me, they don't seem to be following a leader. They all just know when to turn. —Adie C., 12, Washington A. This question stumped scientists until the early 1980s, when a young biologist solved the mystery. By studying slow-motion movies of flocks of sandpipers, Wayne Potts (now head of a genetics lab at the University of Utah) discovered how turns happen. First, a bird near the edge of the flock starts to swerve—always toward the flock, because predators might be waiting outside. Nearby birds get out of the way. Then birds deeper in the flock get out of their way. Birds farther off see the disturbance coming and get ready to turn, too, much faster than if they waited to dodge their neighbors. Any bird can start a turn; the flock has no permanent leader. Potts called his explanation the "chorus-line hypothesis," because it reminded him of the way human dancers synchronize their leg kicks. Computer models show that things really are that simple: if every bird just follows the crowd while keeping a safe distance, together they can pull off amazing stunts. —Robert Q. Why are tigers striped? Q. Why do crabs walk sideways? Q. Do lobsters think? This Q&A column was a joke, though not everybody realized it. D. L. reprinted it from a parody of pre-Muse Q&A columns that she found in one of her quaint and curious volumes of forgotten lore. Because Robert and Rosanne didn't write it, we can't reproduce it here. Q. How much does a cloud weigh? —Eliza M., 7, Virginia A. When you look at a cloud, what you see are water droplets or ice crystals, but the cloud is mostly air. "A typical cloud contains about half a gram of liquid water (or ice, if the temperature of the cloud is cold enough) per cubic meter of air," said Peter Hobbs.* Translated into everyday terms, a half gram is about half a thimble of water. A cubic mter is about the size of three bathtubs. So a thimbleful of water would make about six bathtubs' worth of cloud. The rest of the answer is just arithmetic. A typical fair-weather cumulus cloud, Hobbs said, is about 3 kilometers across and 4 kilometers high (about 2 miles by 2-1/2 miles). It contains about 14 billion grams (or 14,000 tons) of water and 35,000 billion grams (or 35 million tons) of air. That's about as much water as it takes to fill four Olympic-sized swimming pools. A big cumulonimbus storm cloud weighs almost 20 times as much. What keeps all that water in the air? The air does, by blowing the drops upward like popcorn in a hot-air popper. When drops collide, they may combine until they grow too big for the wind to hold them up. Then they fall as rain. —Robert *Peter Hobbs is an atmospheric scientist at the University of Washington. Q. Can all the elements be destructive if their nuclei are split? If not, which ones are destructive? —Adie C., 12, Washington A. At the center of every atom lies a tiny ball of particles called protons and neutrons. Physicists can split this nucleus by firing neutrons at an atom. That splitting (called fission) releases lots of energy, though, only if each atom spits out at least two neutrons that can split other atoms and if splitting releases more energy than the first neutron contained. Physicists know of only a few atoms that meet these qualifications. All are very heavy radioactive elements. The most common ones are called uranium-235 and plutonium-239. Other atoms might work, too, but physicists haven't tested them yet, because it's hard to get enough of them together. By the way, energy from fission doesn't have to be destructive. Kept under control, it can be very useful—just ask the captain of a nuclear-powered submarine. —Robert Two nuclear physicists, Mark Stoyer of Lawrence Livermore National Laboratory in California and Konrad Gelbke of Michigan State University, helped answer this question. May/June 2005Q. What happens when someone tickles you? Why do you laugh? —Yaneke P.., 12, Florida A. Scientists have come up with some interesting theories about tickling. One is that ticklishness inspires us to play—which is good since playing is crucial for our mental health. And the great thing about this game is that it's so simple even babies can play. Laughter is one of the tickle game's signals. It shows that the tickled person is having fun. When the laughter stops, the tickler knows the fun is over and it's time to cut it out. "The truth is, though, we don't really know why people laugh when tickled," admits Christine Harris, a professor who studies tickling at the University of California in San Diego. We're not the only creatures that play tickle games. Chimpanzee mothers also tickle their babies, who laugh chimp-style with raspy panting sounds. Big brother and sister chimps tickle the little ones too. —Rosanne Q. If the Y chromosome is progressively shortening, doesn't that mean it will disappear and there will be no more human males? —Peter D. A. The human Y chromosome isn't going to rot away at all. Until recently, scientists did think the future looked grim for the Y chromosome, which carries the genes that make male humans male. They thought that over the next 5 million years the Y, nearly the smallest human chromosome, would dwindle away to nothingness. The Y seemed to be at risk because—unlike all the other chromosomes—it has no mate. And without a mate, there's no way for the chromosome to repair itself in the usual way, which is to patch the mutation with a good copy made from its partner. Since chromosomes discard defective genes over the generations, the Y chromosome seemed bound to disappear. That was until scientists realized the Y has a debugging system all its own. In the last few years scientists* have found that the Y carries its own backup copies of important genes and can use these to fix clunkers. So it was all a false alarm: the Y's important genes are here to stay after all. —Rosanne *David Page at the Whitehead Institute for Biomedical Research in Massachusetts and Richard K. Wilson at the Washington University School of Medicine in Missouri led the experiments that uncovered the Y chromosome's repair work. Q. Why do we get shadows under our eyes when we lose too much sleep? —Sarah P., 13, Wisconsin A. The skin under our eyes is very thin, so it's easy to see through to the veins underneath. Those veins make the skin look purplish. It gets even easier to see through the skin when we don't get enough sleep. That's because lack of sleep makes our skin paler and dries it out. I asked skin expert Brandith Irwin* about this, and she said: "The circles look worse after no sleep because the eye area doesn't rehydrate completely unless you lie down for seven to eight hours. Dehydration actually makes our skin look thinner, less elastic, and more transparent. "Sleeping is best for those seven to eight hours, but if you're patient enough to lie still for that long without sleeping, I imagine this would alleviate dark circles too!" *Brandith Irwin is a dermatologist at the Madison Skin and Laser Center in Seattle, Washington. —Rosanne Q. How does a water filter work? Wouldn't the water get dirty because of the charcoal? —Juliette R., 11, Illinois A. I sent your question to historyofwaterfilters.com, a Web site run by a commercial water-filter company. A water filter, their writer Vanessa Lausch explained, is made of tiny grains of charcoal or other materials. When water flows through it, those little chunks strain out solid stuff you'd rather not drink—much as big rocks in a river trap logs floating downsteam. Most modern filters also do a more sophisticated trick. Their grains attract molecules of unwanted chemicals in the water, using positive and negative electric charges to trap the chemicals in the filter. Filters like these are used to remove chlorine from drinking water, something ordinary carbon filters can't do. The grains don't get into the water because they're caught in a cage, like grapes in a sieve. Nothing is perfect, though, Lausch said. New filters sometimes contain grains small enough to slip through the mesh. When that happens, you have to rinse the filter until the water comes out clean. —Robert copyright © 2005 Robert Coontz and Rosanne Spector |