Scream and bring down a roaring cascade of snow?  It seems plausible, especially since a single person skiing in the wrong place can trigger an avalanche above.  But researchers say that a human voice doesn’t have the power to move mass quantities of snow.

A powder snow avalanche

According to snow researchers, the idea that avalanches can be triggered by ordinary noise is a (popular) myth.  At an International Snow Science conference in Switzerland this year, researchers presented a paper comparing the human voice to aircraft noise, sonic booms, and deliberate explosions.

All sounds produce pressure waves in the air.  But even the loudest scream produces a pressure wave just one-tenth the amplitude, or magnitude, of a passing plane.  The pressure wave produced by a sonic boom — created by a plane flying faster than the speed of sound — has an amplitude 100 times as large as a scream.  A detonation of explosives produces pressure waves more than seven times as strong as the boom’s.

Scientists say that whether a snow mass shifts depends on the pressure wave amplitude.  They note that a short-lived pressure wave must be at least as strong as that produced by a sonic boom to trigger an avalanche.  So even a low-flying jet  — let along a human scream — won’t start an avalanche.

The avalanche myth may have its origins in the idea that a human voice, singing the right note, can cause a glass to shatter.  That idea, it turns out, is true.

Resonance is the phenomenon behind glass-breaking.  Have you ever swung on a swing, and noticed that if you pump your legs in the right rhythm, the swing will go higher and higher?  Your rhythm has exactly matched the natural rhythm, or frequency, of the swing, and the swing swings higher and faster.

Something similar happens when a musical note shatters an empty wine glass.  A thin, lead-crystal wineglass has its own natural frequency, which we can hear by lightly tapping the glass with a spoon.  A sound of the same frequency will make the glass vibrate.  And if the right sound is also loud and long, the glass may shatter.

But while an amplified voice singing the right note was known to break glass, no one had absolute proof that an un-amplified voice would also work.  Enter the show “Mythbusters,” which used a crate of wine glasses to demonstrate that the human voice can shatter glass.  Watch the “Mythbusters” wine glass episode here.  (But don’t try this at home!)

While a wine glass poses the risk of flying shards, resonating bridges can be even more dangerous.  In England in 1831, marching cavalry soldiers were crossing a suspension bridge in Manchester.  The bridge began to sway, and the troops automatically matched their marching to the motion.  Like a swing powered by pumping legs, the bridge’s swinging steadily increased.  As the bridge oscillated, a bolt broke, and the soldiers fell into the water below.  These days, soldiers are instructed to march out of time with each other when they cross a bridge — just in case.

Spaghetti cooking

Before you is a pile of dry spaghetti.  Your job, should you decide to accept it, is to break each piece in half, so that the pasta fits easily into a small saucepan.  Ready, set, snap…Oops.  What should be a snap is actually frustratingly difficult, as tiny, broken bits of pasta litter the table.

Scientists tried to solve the broken pasta problem for years.  Most famously, the late physicist (and Nobel Prize winner) Richard Feynman spent an evening with friend (and supercomputer expert) W. Daniel Hillis, snapping spaghetti.  At the end of the night, there was a pile of broken spaghetti, but no satisfying theory.

But in 2005, two physicists in Paris may have solved the spaghetti puzzle.  The scientists took high-speed images of breaking spaghetti, and applied a mathematical equation describing how waves travel through a stressed object.  What they found:  As a piece of spaghetti is bent until it can curve no longer, it breaks.  The sudden release causes a burst of “flexural waves” to travel through the remaining pieces, causing them to curve sharply, too — leading to more breaking.

So in a split second, your pasta breaks into three or four pieces, instead of neatly in two.  (Watch dry spaghetti bend and fragment at www.youtube.com/watch?v=8GutricnMNc.)

Once you’ve cooked your broken (or intact) spaghetti and added sauce, you may be in the mood for slurping.  But while it’s fun to hoover up strands of spaghetti,  you could find the tablecloth–and everyone around you–covered in a fine spray of crushed tomatoes.

How come?  According to physicist Jearl Walker, of Cleveland State University, the culprit is…wait for it…the Spaghetti Effect.  It turns out that the Spaghetti Effect doesn’t just apply to pasta drawn into your mouth, but also to paper, metal, and other materials pulled into machinery.

Walker says that when a spaghetti strand is lifted from your plate, it already has some sideways swinging motion.  As you suck up the spaghetti, you leave less and less of the strand hanging free.  So the energy of motion–the kinetic energy of the strand — is concentrated in a smaller and smaller piece of strand.  Just before the strand disappears into your mouth, its sideways motion becomes violent enough to fling sauce across the table.

You can also see the Spaghetti Effect in action between meals, whenever you use the vacuum cleaner.  After you’re finished sweeping the living room, unplug the vacuum and press the cord rewind button.  As the spaghetti-like cord is sucked quickly into the base, it may begin to whip around, turning the metal-tipped plug into a moving hazard.  The solution:  Retract the cord slowly, with several gentle pushes of the button.  (And if you must slurp pasta, try to do it in slow motion.)

Actually, there are bars at the center of most spiral-shaped galaxies.  But you won’t find any drunken Wookies or neon Budweiser signs, only vast sweeps of dust and stars.

A barred spiral galaxy

Galaxies are enormous, turning cities of stars. There may be a hundred billion galaxies in the universe, separated by vast stretches of mostly empty space. Galaxies come in several basic shapes; the most common are a simple elliptical or a spiral, like a pinwheel.

Our home galaxy, the Milky Way, is a collection of at least 100 billion stars (one of them the Sun), arrayed in a rotating spiral.  As Earth and its siblings planets orbit the Sun, the Sun traces an almost circular orbit around the galactic center.  Traveling along a spiral arm at about 490,000 mph, it takes the Sun some 220 million years to circle once around the Milky Way’s core.  (The last time the Sun was near its current position, dinosaurs roamed North America.)

Such distance are measured in light-years, the distance light can travel in a vacuum in one year (about 6 trillion miles).  Luckily, our solar system cruises through the galaxy’s outskirts, about 26,000 light-years from the core — where lurks a massive black hole.

At least two-thirds of all spiral galaxies have bar-shapes running through their centers, created by dust and millions of stars in very peculiar orbits.  Instead of traveling in near-circles, the stars are orbiting the galactic center in long, bar-shaped loops.

But it wasn’t always so.  Since light from distant galaxies can take billions of years to reach Earth, looking out into space is looking back into time.  And scientists say that the spiral galaxies of 7 billion years ago were much less likely to have bars.  Since the universe is about 13 billion years old, it seems like bars may be the signature of a mature spiral–a grown-up galaxy in the prime of its life.

How do bars form?  The enormous gravitational pull of the galaxy’s center keeps stars in orbit.  Computer models show that over time, as orbits are disturbed by stars’ gravitational attraction to other passing stars, circular orbits can become more elongated.  As orbits stretch out, stars travel toward and then away from the galactic center.  Gradually, over many millions of years, enough stars are locked into long, narrow orbits to form a visible bar across the galaxy.

But bars aren’t just a scenic galactic feature.  The orbiting stars’ gravity pulls more gas, the raw material for new stars, into the inner galaxy.  This may explain the ring of glowing gas around the center of many galaxies, studded with newborn suns.

On the less-cheery side, the oldest stars in a bar tend to follow the most elongated paths, carrying them closest to the galaxy’s center.  In our Milky Way, such bar-crawling old stars may fall into our galaxy’s black hole, disappearing with a burst of x-rays.

View a photo of a barred galaxy at http://apod.nasa.gov/apod/ap050112.html.  See an artist’s conception of the Milky Way at http://apod.nasa.gov/apod/ap050825.html.

If we could look closely at our ceilings, we’d see the crisscrossing paths of thousands of tiny footprints, left by flies, ladybugs, and other insects (as well as by spiders).  In fact, the problem for flies and other bugs may not be holding onto the ceiling, but breaking free from it.  Turns out, a fly strolling across a ceiling is a bit like a person walking across a field of wet mud.

How do flies walk upside down, apparently effortlessly? Being tiny certainly helps.  Very-low-mass animals like wall-walking insects and spiders feel less of a pull from gravity.  So it’s easier for a fly than a pig to stick to the ceiling (even Spiderpig needed Homer’s help).

On a rough surface, an insect can use its claws, rappelling up or across like a climber on a rock wall.  But many insects and spiders also rely on special leg or foot pads, often covered with bristly hairs, when they need to climb up surfaces.  Scientists once thought that the rough, bumpy hairs allowed flies to cling to tiny nooks and crannies on even smooth-looking surfaces, including ceilings.  A substance secreted by the hairs helped, adding a bit of adhesion.

But in 2006, scientists at the Max Planck Institute in Germany discovered that the substance secreted by the hairs on a fly’s feet is a sticky glue, tailor-made for striding confidently across the ceiling, upside-down.

The glue-y stuff oozing out of a fly’s footpad hairs is a mixture of oils and sugars.  Researchers say that all insects may secrete the glue, since all 300 wall-climbing insects studied at the Institute left a trail of tiny, sticky footprints on the wall.

The adhesive is strong enough to keep each foot planted on the ceiling, fly standing still.  Walking, however, isn’t trouble-free.  Although the journey across the top of a room may look effortless from our perspective, it’s a struggle for the fly.  The researchers found that flies use at least four different techniques to get a foot unstuck and moving again.

Watching slow-motion tapes of each foot detachment, scientists found that a fly sometimes pushed a foot away from himself, popping the footpad off the surface like a freed suction cup.   Flies also twisted their footpads until they loosened from the wall, or jerked them quickly like a yanked-off band-aid.  Flies also used the handy, built-in claws on their feet to pull a footpad off the ceiling, like a person tugging off a boot.

According to the scientists, the techniques that involved peeling the pad off the ceiling or wall work best, because they require less energy.

Using four of six legs as they crawled across the ceiling also helped the flies make their gravity-defying journeys.  (On the ground, scientists say, flies often use just three legs at a time to move around:  two legs on one side and the middle leg on the other, forming a stable triangle, alternating sides with each step.)

No one’s sure where the myth started, but it has legs (er, wings):    Bumblebee flight is impossible.  According to the principles of aerodynamics, the story went, a big, fuzzy bumblebee, powered only by tiny wings, shouldn’t leave the ground.  A French book from the 1930s, for example, cited calculations that “proved” insects in general shouldn’t be able to fly.  But using mechanically-driven fixed aircraft wings to model the flight of bumblebees and other insects just didn’t work.

The mysteries of insect flight are still being unraveled, but today’s scientists say insects fly “in a sea of vortices,” using the swirling eddies of air created by their beating wings to stay aloft.

Bumblebees beat their wings up to 200 times a second, faster than the nerve impulses to their muscles can fire.  This works because bumblebee wing muscles don’t contract and expand with each electrical signal.  Instead, they continuously vibrate, like a repeatedly plucked guitar string.

When a bumblebee rests, its body temperature drops (or rises) to that of its surroundings. But according to entomologists, the temperature of a bumblebee’s wing muscles must be a toasty 86 degrees F. to lift the bee into the air.  So to fly to the nearest flower cafeteria, a bumblebee must dramatically raise its temperature in all but the hottest weather.

How?  Basking in the sun isn’t usually enough, so the bee will shiver her way to a higher temperature.  By rhythmically contracting and releasing her abdominal muscles (faster and faster as her temperature rises), a bee generates enough warmth to take flight.  The warmer the air temperature, the quicker the lift-off.  On a chilly, 42-degree day, a bumblebee must pump her thorax muscles for a tiring 15 minutes to reach 86 F.

Once in flight, a bumblebee’s muscle temperature remains in a range of about 86 to 111 F.  All of this activity expends enormous amounts of energy, provided by the sugars in flower nectar.  Not surprisingly, scientists have found that bumblebees are especially attracted to warm flowers, floral rooms whose color and shape keeps them heated in the sun.

According to Oxford University research published this month, bumblebee flight really is different from that of dragonflies and other insects.  Using a smoke-filled wind tunnel and cameras snapping 2,000 images a second, researchers found that bumblebee flight is surprisingly inefficient.  For example, a bumblebee’s left and right wings flap independently of each other.  And instead of using the varying air pressure at its wingtips to provide some lift, bumblebees use “brute force” to fly and hover.  Bumblebees, say scientists, are the “tanker trucks” of the flying insect world, using incredible amounts of energy to lumber (charmingly) through the sky.

In fact, bumblebees manage to fly even in places where human beings find it difficult to breathe.  On Earth’s highest peak, Mount Everest, bumblebees have been sighted at more than 18,000 feet up.  Although there’s much less air pressure for tiny wings to beat against, bumblebees power on, hot to the touch even in the frigid cold.

It begins to pour.  You have no umbrella, or printed newspaper.  (The internet, alas, won’t keep your head dry.)  Never mind singing in the rain.  The question is, To run or not to run?

Assuming you’re healthy enough for a mad dash to that building across the street (or the shelter house in a public park), is it worth the energy?  Can you really slip between the drops?  Or will sprinting through a downpour actually make you wetter?

At first glance, the answer appears obvious:  Running means less time spent in the rain, and less-wet clothing.  But the walking advocates have arguments that seem to make sense, too.  If you run through falling raindrops, they point out, you’ll catch more raindrops on the front of your body — chest, stomach, fronts of legs.  If you walk, most of the drops will fall on your head.  Since the front of your body has more surface area than the top of your head and shoulders, you’ll get more water-logged if you run into the wall of rain.

Some have even done mathematical simulations that say you’ll be wetter if you run.  With rain falling straight down from the sky, and no wind, they argue, you’ll scoop up water through the rain field as you dash forward.  But actual experiments with real human beings have found otherwise.

According to physicist Jearl Walker, of Cleveland State University, running keeps you drier because you spend less time being pelted with water.  If there’s no wind, or the wind is blowing toward you, Walker says, you can minimize the number of drops your body encounters by leaning forward, while running as fast as you can.  With a wind at your back, he advises matching your speed to that of the horizontally blowing drops.  Moving with the rain, he says, you’ll avoid both front and back splatters; most drops will strike your head.

And in a 1997 report in the British journal Weather, two climate researchers in Asheville, NC also found that running trumps walking.  On a rainy day, Trevor Wallis and Thomas Peterson suited up in identical sweats, wearing trash bags underneath so that water wouldn’t soak through.  One ran and the other walked through the pouring rain over a 100-meter (328-ft.) course, weighing their track suits before and after their wet dash/stroll.  What they found:  The clothes of Wallis, who ran, were a full 40 percent drier.

If you’re already soaked, or the nearest shelter is very far away, it probably doesn’t matter whether you walk or jog.  To find out if it’s really worth breaking into a run in the rain, physicist Doug Craigen has devised a handy calculator.  You’ll need to enter your height, take some body measurements, and guess at the wind speed of your own rainy day.  Find out how wet you’ll get at   http://www.dctech.com/physics/features/0600.php.

Ever add sugar to a cup of microwaved tea, only to have the tea (startlingly) boil over?  Boiling depends on bubbles, and sugar can make hot water more bubbly.

Boiling is evaporation, but fast and furious.  We can actually see the water leaving, as a cloud of steam.  It can take days for a room-temperature glass of water to evaporate, but a small pan of water can boil away in a matter of minutes.  That’s because when water reaches its boiling temperature (212 F. at sea level), it evaporates not just from the surface, but from deep within.

Adding sugar (or other ingredients, like salt) can make extremely hot water boil, or cause already-boiling water to boil faster.  How come?  Boiling begins with bubbles.  The first bubbles to appear on the walls of a heating pan of water are actually air that was dissolved in the water, re-emerging as a gas.  But as the bottom of the pan gets hot, liquid water itself begins to turn to gas.

Water begins forming vapor bubbles at hot spots here and there on the pan bottom.  Steam bubbles form most easily on a rough, uneven surface.  Tiny crevices are ideal “nucleation sites,” places where bubbles can get a foothold and grow.

When steam bubbles inflate, break free, and begin to rise, their journey is short-lived.  As a bubble floats up into cooler water in the middle of the pan, it collapses like a deflated balloon.  Why?  At lower temperatures, a bubble’s pressure drops, allowing the kitchen air — the local part of the Earth’s atmosphere — to crush it.

But when the water’s temperature reaches the boiling point throughout, the pressure in the vapor bubbles increases to that of the air.  Bubbles from down under can then rise to the surface.  Where, with tiny pops, they release their vapor into the air.

When you drop sugar (or salt, or powdered sweetener) into boiling water, the crystals provide a raft of new nucleation spots.  Presto–a crowd of new vapor bubbles forms, creating a short-lived fizzy effect.  But add sugar to microwaved water, and the effect can be much more dramatic.

When you heat a cup of water or tea in the microwave, its temperature can rise several degrees above the boiling point — while the liquid remains still and bubble-free.  Why?  When water isn’t heated from the bottom up, there are fewer hot spots.  Meanwhile, in a smooth glass or ceramic cup, there are few nucleation spots.  The result:  Water can “superheat,” without boiling.

Remove your superheated cup of tea and add sugar — or drop a teabag into superheated water — and the results can be explosive.  Runaway nucleation can cause the tea or water to suddenly boil furiously.  Scalding liquid may pour over the sides of the cup, or even spray into the air.  The lesson:  You can’t tell how hot the water is just by looking.  When in doubt, let microwaved liquids sit a while before moving.

At breakfast on the International Space Station, a splotch of orange juice can land on your shirt–even if it was spilled by someone across the room.  That’s because in the microgravity of the space station, spilled liquids collect into round, floating drops.

Liquids, content to wait at the bottom of a glass on Earth, behave very differently in the near-weightless conditions found in the orbiting space station or shuttle.  According to NASA scientists, the pull of Earth’s gravity on the space station and its occupants is substantial:  about 90 percent of the force at the Earth’s surface.  But since the space station is continuously falling around our planet, the astronauts and objects on board are in a kind of free-fall, too, and feel nearly weightless.

So what makes liquid water ball up in microgravity?  Molecules in a parcel of liquid water are mutually attracted, but can slip and slide past each other.  That’s how liquid water, unlike solid ice, can take on the shape of the container it’s poured into, such as a drinking glass.
But water molecules at the surface aren’t much attracted to gas molecules whizzing in the air above them.  Their main attraction is downward and sideways to other water molecules in the glass.  The result is a tense, tight surface–almost like a thin, rubbery skin on the water.  (Some insects can walk across this “skin” on the surface of a pond.)

This surface tension is the key to the shape of liquid water spilled in microgravity.  Water is free to leave an open container in microgravity, since gravity isn’t keeping it pinned to the bottom.  As a parcel of water free-falls in the space station, surface tension pulls the water into a sphere.  How come?  Since the parcel is free-floating blob, it has one smooth surface exposed on all sides.  All molecules on the surface tend to be tugged down and sideways with equal tension by their fellow molecules.  And so the blob of water pulls into a compact sphere — the most efficient shape in nature, with the smallest possible surface area.

(Watch a water balloon burst in microgravity at www.space-video.info/misc/balloon.html.)

We can see the surface tension effect on Earth each time it rains.  Water free-falls from clouds as drops, each held in its own “bag” created by surface tension.  The tear-shaped raindrops would be round spheres if it weren’t for the drag of the air they fall through.

Scientist and astronaut Don Pettit worked on the space station for five months in 2003.  In his “Saturday Morning Science” experiments, he was often astonished by the behavior of liquid water in near-weightlessness.  Watch Pettit’s experiments with water spheres (including inserting a tablet of Alka-Seltzer) at www.freesciencelectures.com/video/waves-bubbles-and-reactions-in-a-free-sphere-of-water.  Bored with drinking tea the old-fashioned way?  Watch Pettit consume tea blobs with chopsticks at http://science.nasa.gov/ppod/y2003/07apr_hightea.htm.   Many more videos of Petit’s adventures with weightless water can be found on Youtube.

Listening for the echoes of their own rapid-fire, high-pitched calls, bats navigate the night, while snatching tiny insects from the air.  Dolphins (along with many whales and shrews) are also skilled “echolocaters.”  And it turns out that we humans, too, are capable of using a kind of sonar, and getting better with practice.  In fact, in the 1800s, one blind man used a kind of echolocation as he traveled the world, mostly on foot, writing about his adventures in a series of books.

Bats are the experts at traveling — and hunting — by listening.  Like submarines in the murky ocean depths, bats move through a sea of echoes, “picturing” objects in their way.

Bats emit high-pitched sounds through their mouths or noses, using their big, oddly-shaped ears to listen for sound reflections.  A bat may sweep your dark yard with sound at 10 blips a second.  When the sounds echo off an insect, the bat increases the rate, giving it a better sense of the bug’s size and location.  As the bat zeroes in, it chirps faster and faster, up to 200 times a second.

While human beings would lose a sonar throwdown with bats, some sight-impaired people do develop the ability to echolocate.  The simplest form of echolocation is tapping a cane or stick while listening for the echoes.  This gives the walker a sense of the changing terrain, as well as objects along the path.  But some people also use clicking or other sounds, much like bats, to determine the location, size, shape, and composition (hard or soft) of objects around them.

California teenager Ben Underwood, blind since he was a toddler, navigates using a series of fast tongue clicks.  Underwood says he began using clicking as a young child, and can even sink baskets by listening for echoes from the basketball pole and backboard.  One scientist estimated that Ben’s sonar clocks in at about 120 clicks a second.

Daniel Kish, a California psychologist who is also blind, practices and teaches echolocation.  His students have even learned to mountain-bike using the human form of sonar.

The first well-known human practitioner of echolocation was James Holman, born in 1786 with normal vision.  James was only 12 years old when he enlisted in the British navy, rising to lieutenant by his 20s.  Then, after an illness involving severe joint pain, Holman lost his vision at 25.

Holman decided to travel the world, using a walking stick and listening for resounding clicks as he trekked through Europe, Asia, Africa, and South America.  The books he wrote about his sometimes-perilous journeys were bestsellers in the 1800s.  After his death in 1857, the so-called “Blind Traveler” was gradually forgotten.  His story is recounted in the book “A Sense of the World:  How a Blind Man Became History’s Greatest Traveler,” by Jason Roberts.

For more on Holman, listen to an interview with Roberts at www.npr.org/templates/story/story.php?storyId=5675082.  For more on Ben Underwood and Daniel Kish, go to  http://abcnews.go.com/Primetime/story?id=2283048.

It’s the heartbreak of dropped toast.  You tip your plate or lose your grip or bump the table.  In the blink of an eye, your toast is, well, toast: the buttered side stuck to the floor, its surface studded with dust, grit, and cat hair.

But don’t blame the cow.  Toast also lands jam-side down, peanut butter-side down, and, in the U.K., Marmite-side down.

The falling toast effect is one of the most popular examples of Murphy’s Law:  that whatever can go wrong, will.  People have been dropping their buttered toast on the unforgiving floor (and complaining about it) for centuries.  In 1841, an Ohio newspaper called The Huron Reflector published a bread lament:

“I never had a slice of bread, Particularly large and wide, That did not fall upon the floor, And always on the buttered side.”

By the end of the 20th century, science had caught up with what the rest of us already suspected.  U.K. researcher Robert Matthews conducted a scientific investigation of the dynamics of buttered toast.  The result was a 1995 report in the European Journal of Physics, “Tumbling toast, Murphy’s Law, and the fundamental constants.”

In the paper, Matthews noted that the prevailing view among scientists at the time was that there was no toast problem.  Like flipping a coin, toast dropped enough times should land 50 percent of the time on the plain side, 50 percent on the spread side.

And a BBC science show experiment in the early 1990s seemed to support that conclusion.  Volunteers threw their toast into the air.  Of 300 tosses, 152 landed butter-side down, 148 butter-side up.  The conclusion:  the chances of buttering your floor are about 50-50.

But Matthews found this wasn’t the case.  In real life, toast isn’t tossed up into the air.  Instead, it slips off a table or a plate, and usually does land on the buttered side.

How come?  While it seems like the weight of the butter or other spread is to blame, Matthews says it’s the height the toast falls from that’s crucial.   When toast — resting buttered-side up — slips off a standard-height table, it tends to flip over.  Why?  When the center of the slice — which is the center of gravity, if the toast is buttered evenly — moves beyond the edge of the table, the toast begins to rotate over the edge.

If the distance to the floor isn’t far, the toast won’t have time to do a full 360 in the air.  So toast falling about 3 feet usually lands butter-side down.  If the toast has far to fall, it could go either way:  angular momentum will cause it to spin end-over-end, but air resistance will slow it down.  And if it happens to spin, say, 1.5 times, it’s buttered linoleum all over again.

The tumbling toast effect, Matthew says, “seems to be an ineluctable feature of our universe.”

For more toast experiments, visit www.thenakedscientists.com/HTML/content/kitchenscience/exp/butter-side-down.