The Science Of Summer

SAND: Building a Castle in the Sky

The 80 master sand sculptors gathering at Harrison Hot Springs in British Columbia next month for the 2001 World Championship won't build their mermaids, cathedrals, swans and Bill Clinton caricatures with just any grains of sand. They chose Harrison, where they'll use about 700 tons of sand and 400 tons of water, because its sand "is very angular," says Bob Bell, general manager of the competition. "It isn't surf-rolled into ball bearings like you get at ocean beaches." Angular means sticky, because the more corners and protuberances in the grains, the more they act like rocks in an old stone wall. Florida and Hawaii also boast angular grains, mostly pulverized corals and shells or crystallized volcanic lava. But California beaches, as well as Atlantic beaches north of Florida, have quartz sediment from inland mountain ranges. The journey to the coast, usually via streams, wears down the rough edges, creating round grains.

Whether sand is castle material or not depends on how it interacts with water, that magical mortar of summertime. Water creates a capillary force between the grains, says physicist Peter Schiffer of Notre Dame University. If the grains are too round, so much water can get between them (put four cherries together to see how much space exists between round solids) that it pushes the grains apart, says geologist Kenneth Lacovara of Drexel University. But the rougher the grains, the stronger the friction between them, and the stronger the capillary forces. Sand sculptures endure even after they dry out: as salt water evaporates, it leaves behind tiny salt bridges that bind the grains.

TASTE: We All Scream For Ice Cream

Human beings can taste only five flavors: sweet, sour, salty, bitter and umami (a kind of meaty, Parmesan-cheesy flavor). Yet somehow we taste well enough to warrant a second late-night drive back to the supermarket, this time for the good kind of coffee ice cream. The tongue, the front line of taste, is covered with bumps called papillae, which house the taste buds, onion-shaped clusters of 50 to 100 cells. The more buds you have, the more sensitive you are. In nature, bitter things are poisonous or spoiled (or heavy investors in tech stocks). Sweet is the taste of carbohydrates, the body's fuel. So we're evolutionarily programmed to want boardwalk food: funnel cakes, cotton candy, frozen chocolate bananas. Umami, from the Japanese for "delicious," is the flavor of the amino acid glutamate, as in monosodium glutamate. It's also a neurotransmitter, a molecule cells use to talk to neurons. So researchers searched for a receptor, a length of protein dangling from a taste cell like a fishing line, that looked like known glutamate receptors. They found it, explaining why MSG makes food more savory. Bitter and sweet turned out to work the same way. Salty and sour, on the other hand, work through charged particles called ions. Sodium ions in salty food and hydrogen ions in acids (think lemons) squeeze through pores in taste cells' membranes.

Smell plays a crucial role in taste. Retronasal olfaction--chemicals in food evaporating up to the nose via the back of the throat--is literally the spice of life. It's the cilantro in salsa, the peat in Scotch. As people age, their sense of smell weakens, so they don't taste as well.

Any taste bud can perceive any flavor. So the map of the tongue in all the textbooks that shows sweet tasted in the tip and bitter tasted in back is wrong, a misinterpretation of the work of a 19th-century German researcher. In other words, just a slip of the tongue.

VIEWS: Why Scenery Makes Us Happy

If you can't quite figure out why the price of that summer rental was sky high, look out the window: as both real-estate agents and scientists know, views are valuable. The perfect landscape has grassy rolling hills, small clusters of trees and a manicured lawn, say psychologists, who find that humans across cultures prefer these pastoral settings. It's probably not a coincidence that humans evolved millions of years ago in just such an environment: the African savanna. Such views, says psychologist Roger Ulrich of Texas A&M University, fill us with a sense of "security, a feeling of easy access to food and low exposure to predators and disease"--which, after all, top most everyone's list of summer-rental musts.

Our ancestral legacy predisposes us to like savanna like views more than dense forest, desert, mountains or coasts, though many people appreciate the beauty of all four. In decades of studies, Rachel and Stephen Kaplan, who started researching landscape preferences in 1969, find that people are also captivated by "mystery"--landscapes that invite exploration through a bend in a path or a clump of bushes obscuring another feature. Something with life and on a human scale is also appealing. A windowful of the Grand Tetons is awesome, but stick Bambi in the foreground and you can probably double your weekly asking price.

ROLLER COASTERS: Thrills and Chills

No wonder roller coasters can be addictive: some of the physiological effects of a whirl on a heart-stopping monster like the Millennium Force ride in Sandusky, Ohio, are the same as those of a hit of cocaine. The first to break the 300-foot barrier (by 10 feet), the Millennium shoots riders earthward at some 92 miles per hour down an 80-degree slope. During the plunge, the neurochemical dopamine floods the brain, giving the riders a high akin to that from other sources of (legal or illegal) pleasure.

Coasters toy with the body as well as the brain. The adrenaline rush induced by the speed and hairpin turns increases heart rate and heightens arousal. Acceleration compresses the body against the seat, flattens the eyeballs and makes the waistline bulge out at the sides in a particularly fetching way. At the bottom of a dip or a loop, G-forces produced by speed and turn radius can reach five times the force of gravity. That makes a typical 12-pound head feel as if it weighs 60, and if five G's are sustained for more than about four seconds, you black out: the heart can't pump the now heavy blood to the brain. And if you don't compensate for a turn, your skull can smack against the restraints with quintuple the usual force, possibly causing bleeding in the brain.

Nothing ruins a good ride like lateral forces that make the train (and skull) knock back and forth. To minimize them, engineers bank curves, explains John Gordon of the Utah-based coaster-testing firm GMH Engineering. Poorly balanced wheels and track imperfections can also cause bad lateral vibes. Negative G's, though, are part of the thrill: generally experienced on the crest of a hill, they make you feel you're rising out of your seat. The weightless part feels great; the sensation of your lunch also rising to the occasion does not.

BASEBALL: The Crack (Or Thunk) of the Bat

To baseball fans, the sharp crack of a bat is one of the sweetest sounds of the game (at least if your team is up). But to an outfielder, that sound is a nightmare: it means head for the warning track. A think, though, tells an outfielder to race in to snare a fast-falling blooper. Since the ball's hang time is usually no more than five seconds, sound clues give the fielder a crucial jump on the ball long before he can see how far it's going: if a ball is hit at a center fielder playing 300 feet deep, one that will take five seconds to land 50 feet in front of him has an almost identical trajectory in its first two seconds as one that will take 4.3 seconds to land 50 feet behind him and one that will take 4.6 seconds to drop into his glove if he stays put. "If an outfielder waits until he can visually tell where the ball will land, that takes almost two seconds," says physicist Robert Adair of Yale University, who unveiled his study of bat sounds at a meeting this summer of the Acoustical Society of America. Two seconds can spell the difference between a put out and a hit.

What determines the sound? A wooden baseball bat is (trust us) not that different from a guitar string. When struck almost anywhere, it vibrates energetically, at a fundamental frequency of 170 cycles per second. "A lot of energy's lost in that vibration," says Adair, the National League's official physicist in the late 1980s. The energy-sapping vibration can hurt the hitter's hands. It also leaves less power for the bat to transfer to the ball, and it makes a sullen thunk--the sound of a ball that's staying in the park.

If the bat connects near its sweet spot, however, it vibrates very little, much as a tennis racket feels solid if you hit the ball on the racket's sweet spot. In the bat, that magic spot is called a node; hitting the ball there produces virtually no energy-sapping bat vibrations. The "crack" is the sound of air being expelled from between bat and ball. The ideal place to hit the ball, concludes Adair, is where three nodes cluster, in the fattest part of the bat. With a bat speed of 70mph, an 85mph pitch smacked near a node will sail 400 feet, good for a home run almost everywhere but straightaway center. A ball hit a mere five inches down the handle will be an easy 310-foot fly out.

TRAFFIC: Stuck in The Madding Crowd

The easy explanations for traffic jams--overcrowded on-ramps, lane-blocking accidents, idiots who won't get out of my freaking way--don't cut it. They don't cover why stop-and-go traffic on the way to the beach can stretch for miles and then suddenly dissipate to glorious free flow.

Traffic is what physicists call "nonlinear." That means that tiny perturbations in the drivescape get magnified into migraine-inducing congestion. It works like this: way up the road--"downstream" in traffic talk--a slow driver slips into the fast-moving left lane. The speedster behind him eases off the gas a little, and the guy behind him overreacts, taps his brake. Pretty soon there's a shock wave of slowing-down-ness propagating upstream. Space between cars in the left lane shrinks, and adjacent lanes start to fill up. The shock wave propagates wider and faster upstream until eventually it's a pointillist wall of red taillights.

It gets worse. The front unclogs more quickly than new cars join the queue in back, so the return to free flow ripples upstream. The leftover phantom jam might be miles away from its origin.

The flip from free flow to congestion is a lot like a phase transition from liquid to solid. If everyone drove a little more slowly, closer to the car in front--no crazy lane changing--we'd all get there faster, like a big block of ice sliding down the highway.

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