Posts Tagged ‘physics’
After Thousands of Years of Research, We’re Still Trying to Figure Out Static Electricity
Static electricity has been under investigation for a few millennia now, with research dating back to the ancient Greeks. But the Northwestern team wasn’t convinced that everything was as it seemed. So they applied to the problem, which allowed them to see the varying levels of charge distributed unevenly across the surface of objects.
What they found is that these charges are far less uniform than previously thought, and that clumps of positive and negative charge are strewn unevenly across surfaces. It’s these clumps that are transferred between objects when they come in contact, not just the charges.
In normal human language, that means that when you rub a balloon on your hair to make it stand up, there is a small exchange of matter--tiny bits of balloon actually adhere to the hair, disrupting the electrical patchwork on the balloon and causing that strange attraction between it and other objects that we all know as static electricity.
That matter exchange is proven pretty definitively by this research, but like most discoveries, this one begets more questions. Why do these negative and positive clumps exist, and does knowing that they do exist fully explain the static phenomenon? Scientists still aren’t sure. And that, boys and girls, is why we never stop learning.
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Video: Weighted Ping-Pong Balls Fall Indefinitely Through a Granular Medium
Defying intuition, dense enough materials can reach terminal velocity within granular solid media.
Specifically, the team used a set of 18 weighted ping-pong balls ranging from 15 to 182 grams (that's not even a half-pound at the high end), and launched them into a large tube filled with polystyrene beads. One would imagine, normally correctly, that a ball would enter the polystyrene medium and begin to lose velocity via friction and the beads' resistance to the force of the ball, eventually coming to a stop depending on how heavy it is and its velocity upon impact.
But it turns out that this is not a universal rule. We know that objects falling through a fluid can reach a terminal velocity because molecules in fluid move aside easily under an applied force. Granular materials don’t share this property; their grains don’t move as easily under an applied stress. This is why bocce balls don’t sink straight into a sandy beach and why meteors that impact planets or moons covered in a granular crust rapidly still stop at a relatively shallow depth.
But in their study, the ping-pong balls that surpassed a certain critical mass--in the case of their granular polystyrene medium, this mass was about 82 grams--traveled all the way to the bottom of the tube. Moreover, their velocities leveled off, reaching a constant velocity just as they would if falling through a fluid.
Through simulations, the researchers showed that the heavier balls would fall indefinitely through the granular medium if they were allowed to. From a physics standpoint this actually makes some kind of sense, though it seems to run counter to intuition. We think of things losing energy in granular media because they usually do. In order to hit that terminal velocity, the upward drag force and the pull of gravity (dependent on the objects mass) have to balance. This is why mass is critical, and why we don’t tend to see this in the natural world.
For instance, in order for a weighted ping-pong ball to fall indefinitely through the sand of an average beach, it would need to weigh about 31 pounds. That requires a really dense material, denser than we find on this planet. More details for the curious via PhysOrg below.
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Possible Sighting of Dark Matter Lights Up Physics Community
Seasonal variation in data indicates that mysterious dark matter may have been under our noses all along
If they’re accurate, the new findings would back up previous research from an underground lab beneath a central Italian mountain, which has proved controversial for nearly a decade.
The new result comes from the Coherent Germanium Neutrino Technology (CoGeNT) experiment at Minnesota’s Soudan mine, where detectors are looking for the faintest interaction between WIMPs and atoms inside a germanium crystal. Researchers led by Juan Collar at the University of Chicago’s Kavli Institute for Cosmological Physics studied about 15 months of data — not very much, but they were interrupted by a fire in March.
They saw signs of a seasonal variation in the interactions between WIMPs and germanium crystals, according to the Kavli Institute. It’s not a WIMP signal per se, but it’s what you would expect to see from a WIMP signal, Collar said. WIMPs are thought to be particles of dark matter, which makes up about 23 percent of the universe.
It's hard to see these ineffable particles because they do not interact with the electromagnetic or strong nuclear forces. This is one reason why detectors are buried underground, into old abandoned mines — thick rock layers shield the instruments from background radiation and cosmic rays that could block out a super-faint signal from a passing WIMP.
The detectors picked up an average of one WIMP interaction per day for 15 months, with a seasonal variation of 16 percent. (For a more thorough explanation of the results, read an extensive interview with Collar .)
Along with echoing the previous Italian experiment, this fits with accepted theories of how Earth encounters dark matter clouds in our galaxy.
As Earth enters the summer portion of its orbit around the sun, its movement is aligned with the direction of the sun’s own movement in the plane of the Milky Way. This increases our planet’s net velocity through a cloud of dark matter particles that permeate the galaxy. Scientists can infer the existence of the dark matter cloud, and they know the Earth is hurtling through it, so it would make sense that we would see an increase in dark matter signals during the spring and summer. That’s what this result claims to see.
A few years ago, the DArk MAtter/Large sodium Iodide Bulk for RAre processes (DAMA/LIBRA) experiment at Gran Sasso, Italy, claimed to see the same thing. But many physicists have dismissed those findings. Then in 2009, another experiment at the Soudan mine, the , found the heat signatures of possible WIMPs.
In a , physicists Dan Hooper of Fermilab and Chris Kelso from the University of Chicago reviewed the data from CoGenT and DAMA/LIBRA, and said the numbers are compatible. "If the true phase peaks in early May, this would represent a modulation consistent with that reported by the DAMA/LIBRA collaboration," they say.
Collar said the team is still working out whether their results just barely exclude DAMA’s results or just barely agree with them. Meanwhile, Hooper and Kelso said another dark matter experiment, the CRESST collaboration, is reporting findings that are also roughly consistent with the purported particle spotted by CoGeNT.
But here's the rub: other experiments, including one in the same mine, have found no dark matter indications. So which one is to be believed?
“It’s not an exact science yet, unfortunately,” Collar said. “But with the information we have, the usual set of assumptions that we make about the halo and these particles, their behavior in this halo, things seem to be what you would expect.”
What does this mean for all of us? Physicists are getting ever closer to nailing down the nature of dark matter, one of the greatest mysteries in science. Understanding dark matter will help us understand the origin and evolution of the universe. With new, ramping up their experiments, and a new dark matter , the future of dark matter studies looks pretty bright.
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Researchers Entangle and Observe Eight Photons Simultaneously, Smashing the Previous Record
As cleverly points out, “getting eight photons exactly where you want them at the same time is the quantum mechanical equivalent of herding cats (clearly of the Schrodinger variety).” Manipulating individual particles at this level is difficult enough, and that’s before you create that quantum link. Once you’ve entangled two or more particles, manipulating the entangled system without breaking the link is even more daunting.
How do you entangle this many photons? You start with one photon from a high energy beam, and you split it with a nonlinear crystal. You now have two weaker photons that are entangled--any exertion on one will affect the other. You put one photon aside in an apparatus and you then split the other, put one of those aside and split the other, etc.
But each split weakens the beam, and previously it was difficult--and time consuming--to produce to a manipulable eight-photon entangled system, so difficult that it hadn’t been achieved. The Chinese team, from the University of Science and Technology of China in Hefei, used a much brighter UV laser capable of churning out more entangled pairs much faster than smaller lasers. Then they figured out how to manipulate them.
That’s significant on a variety of fronts, not least of which is quantum computing. An eight-photon system would allow researchers to probe the quantum world at higher resolutions than was previously possible, demonstrating key pieces of the technology puzzle that should someday enable quantum computers to work as we’ve envisioned them.
For more, .
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Slow-Motion X-Ray Video Reveals the Slurpy Mechanics of Dogs’ Drinking
It’s amazing with a high-frame-rate X-ray camera, a cup of beef broth, and a Portuguese water dog. For instance, we knew that dogs are obnoxious drinkers, but we didn’t realize that rather than scooping liquids into their mouths with the undersides of their tongues, they actually tap a trick of fluid mechanics--just as cats do--to pull columns of water from the water bowl into their mouths.
Thanks to evolutionary biologist Alfred Crompton and some Harvard colleagues, now we know. Crompton’s study of the mechanics of canine drinking published today in the Journal of the Royal Society Biology Letters, and included are the videos seen above and, in X-ray, below. The videos and complementing study show that, contrary to conventional thought on the matter, dogs drink exactly like cats.
from on .
While dogs do pick up a certain amount of water by curling the undersides of their tongues, most of that ends up back in the bowl (or elsewhere). Rather, the flattened tongue barely nicks the surface of the water before snapping back, and when it does so it manages to pull a column of liquid into the air behind it--a column that the canine can then bite down on almost as it would a solid.
It actually takes three or four laps for the dog to work the water along its tongue and the roof of its mouth and into the throat. Which might explain why it seems like that last lap always ends up all over the floor.
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Bodies In Motion: Exploring the Human Limits of Future Travel
The limits of travel are defined not by what vehicles can do, but by what vehicles can do to us. So how much can we take?
As the crew headed north, they received instructions from a Jacksonville controller, first to climb to 26,000 feet, then 39,000. “Three nine zero bravo alpha,” the first officer acknowledged. It was her last transmission. A few minutes later, the Learjet leveled out and the controller issued another routine instruction. No one radioed back. The controller tried to reach the crew five more times in the next four and a half minutes.
When a flight crew is unresponsive, the FAA asks that the nearest military jet make a visual assessment—in this case, it was an F-16 pilot on a test run out of nearby Eglin Air Force Base. Coming even with the Learjet, the test pilot reported that both of the plane’s engines were running. By all indications, the Learjet was in perfect working order. But the test pilot also reported a disturbing detail: The Learjet’s windows were opaque, as if covered from the inside with condensation or ice.
"You can create a system to do whatever you need it to do. But can you keep a person conscious and alive inside it?"It was becoming clear that in the minutes after Bellegarrigue’s last transmission, the cabin had lost pressure and all its oxygen began to escape. Within as little as eight seconds, the crew and their passengers most likely began to experience hypoxia—lack of oxygen in the bloodstream—that impaired their most basic motor and cognitive functions. They may not have even been aware that there was a problem, but within a few minutes of the breach, they were probably dead.
Yet the plane continued on, because a plane does not need its occupants to be comfortable in order to operate. It does not even need them to be breathing.
Corporeal Limits
Humans are flimsy. Our bones snap after a fall of only a few feet. Our flesh ignites at the operating temperature of the average wood-burning stove. The highest human settlements are no more than 19,520 feet up, and none of us can stay alive long past 26,000.
Machines, meanwhile, can take a lot. The wings of a Boeing 777, for instance, can bend as much as 24 feet from their resting position, and any turbulence powerful enough to bend them that far will damage the passengers long before it damages the airplane. In 1997, United Airlines Flight 826, en route from Tokyo to Honolulu, encountered a sudden gust of “clear air turbulence” that crushed passengers into their seats and flung them at the ceiling. The turbulence killed one passenger and injured 70 others. But the pilot was able to return the plane itself safely to Tokyo.
This is the fundamental limit of all forms of travel. “You can create a system to do whatever you need it to do,” says Michael Planey, a former U.S. Air Force engineer and now a consultant for commercial airlines. “But can you keep a person conscious and alive inside it? That’s the challenge.”
How we'll move from place to place in the future will be determined by what passengers can withstand. How fast can the body accelerate? How long can it sit in one place? How many can we pack into a vehicle? Right now we have only a rough sense of these corporeal limits.
Scarce Data
Much of what we know is drawn anecdotally from the violent, often accidental experiences of airmen and astronauts. In 1966 a test pilot named Bill Weaver managed to eject when his SR-71 Blackbird broke apart at Mach 3.18. His systems officer was killed, but at 78,000 feet Weaver survived more than 2,000 mph of air resistance, revealing that a human can in fact withstand incredible shock at a very high altitude, at least when protected by a pressurized suit.
"Comfort is difficult to quantify. We look primarily at safety."In 1960, Air Force captain Joseph Kittinger established as-yet-unbroken records for the highest parachute jump (102,800 feet) and the fastest human free-fall through the atmosphere (614 mph). And between 1947 and 1954, Air Force colonel John Stapp, part of the Aero Medical Laboratory of the Wright Air Development Center, subjected himself to repeated tests on a rocket sled that zipped across what is now Edwards Air Force Base. During one run on his “human decelerator,” Stapp went from 630 mph to a complete halt in just a few hundred feet, experiencing 46 Gs of deceleration.
But standardized data about human tolerances is hard to come by. J.D. Polk, NASA’s chief of space medicine, knows a great deal about the strain of space travel—his astronauts have endured hours of waiting at the launch pad and lived for months in a weightless environment—but even he can’t quite name the breaking point of a human being. That’s because engineers can’t test humans the way they can other components of a spaceship. In designing a space shuttle, “you can stress a part until it breaks,” Polk says. “The human body is the only system in engineering that you can’t take to failure.”
Military and NASA researchers don’t really investigate human comfort, at least not in the way that a commercial traveler might hope. They aren’t attempting to engineer conditions that will convince the traveler to fly a particular airline or buy a particular car. That distinction was highlighted during the Iraq war, when Baghdad International Airport became one of the few places in the world where civilians regularly encountered the discomfort of military efficiency. Rather than the usual long, low approach to the runway, commercial pilots instead had to drop from as high as 35,000 feet in a hard spiral “corkscrew descent,” the better to avoid rockets and small-arms fire. It’s a standard military approach path. But for a civilian, it’s terrifying. “It’s pretty amazing what airplanes can do,” says Tom A. Peter, a freelance reporter who has flown into Baghdad several times. “I’ve never been in a plane crash, but I have to imagine that a corkscrew landing is about as close as you can come without actually wrecking a plane.”
NASA engineer Dustin Gohmert, who designed seat systems for the crew module of the Orion spacecraft, explains the military-civilian distinction in straightforward terms. “Comfort itself is difficult to quantify,” he says. “We look primarily at the safety of the crew.”
Designing for Safety"The human body is the only system in engineering that you can't take to failure."The standards are very high for NASA vehicles. Because a spacecraft can crash hours or days from help, “we have to make it such that the crew can self-rescue,” Gohmert says. And sometimes that means doing away with conventional amenities. In the Orion capsule plan, for instance, Gohmert’s team dispensed with seat cushions altogether. Cushions may separate the body from the hard seat underneath by just a few millimeters, but in a sudden deceleration, the body can close even that small distance with enough force to cause injury. The Orion seats fit each astronaut fairly closely, and the weight distribution makes for a more or less tolerable experience. But comfort isn’t the goal. The seats keeps the astronauts alive.
Of course, NASA also gets to be picky about who comes on board, a degree of selectivity that further limits what the agency can teach us about our own comfort. The Federal Aviation Administration requires commercial airlines to safely accommodate nearly the entire spectrum of humanity, from a 5th-percentile woman (about 5 feet tall) to a 95th-percentile man (over 6'3"). Not so at NASA. To make sure each astronaut fits the operating environment of the spacecraft, the agency assesses not just height and weight, but every measurement of every extremity. If you don’t fit, you can’t fly. “We do three-dimensional body scans of the astronauts as part of the screening,” Gohmert says. “If your femur is too long, it might disqualify you.” Air Force pilots must also properly fit their plane—legs longer than the engineered standard could break when the pilot ejects in an emergency.
Civilian passengers, no matter how tall or wide, expect gentle treatment. As a result, engineers must set extremely conservative tolerances. Rail system designers, for instance, consider the acceptable limit of linear and lateral acceleration (the force exerted on passengers by starting, stopping, and rocking from side to side) to be no more than 0.15 G—roughly what you’d feel on the moon. That limit allows passengers to dispense with seatbelts and walk around freely inside.
But design constraints also act as speed constraints. In 1990, engineers for a federal program called the National Maglev Initiative began to investigate the domestic potential for high-speed magnetic-levitation (maglev) trains—the fastest, a Shanghai airport shuttle, reaches 268 miles an hour. Daniel Patrick Moynihan, then the chair of the Senate subcommittee responsible for the U.S. highway system, had suggested that maglev trains be placed along the median of U.S. highways, so in July 1992, to better understand what it would be like to travel an interstate at maglev speeds, four engineers set out from National Airport in a private jet. “We did 180 mph and began banking as if we were obeying the turns you’d have to make on the New York State Thruway,” recalls Laurence Blow, now a maglev consultant. As the pilot cranked the plane back and forth, simulating the thruway, the engineers began to heave and retch. “It wasn’t the speed or acceleration that made us all sick,” Blow says. “It was the banking.”
Avoiding Nausea
Motion sickness is one of the few areas where civilian desires overlap with military requirements; no commander wants his soldiers or astronauts puking when they need to fight or fly. A lot of data has been generated. In 1995, for example, British naval doctors subjected participants to repeated vertical and horizontal motions while the participants were either seated upright or lying on their backs, and determined that the subjects found horizontal movement while prone to be the most tolerable, and seated horizontal movement to be least tolerable. And a 2006 study established that low-frequency movement (a camel’s gait) is more nauseating than high-frequency movement (a horse’s gait).
The accepted notion, proposed by the English physician J.A. Irwin in 1881 and largely confirmed by NASA in 1970, is that we get sick when our visual input contradicts our vestibular, inner-ear input—when what we see (an unmoving bulkhead) is in conflict with what we feel (sudden acceleration). This is why passengers get sick before drivers or pilots do. “It’s the lack of sightlines that are the problem in the backseat,” says Gary Strumolo, the manager of vehicle design and infotronics at Ford Motor Company. This helps to explain, he says, why even those people who are highly susceptible to motion sickness can often avoid it by driving.
The same goes for air travel. “Pilots on the controls have a foreknowledge of the aircraft motion,” says Catherine Webb, a psychologist who studies motion sickness at the U.S. Army Aeromedical Research Laboratory at Fort Rucker, Alabama. For passengers, she explains, “expectations of aircraft motion often conflict with actual motion, and sickness often results.”
The drug dimenhydrinate, sold under the brand name Dramamine, can help, but it also causes drowsiness and can sometimes even act as a hallucinogen. NASA, eager for a substitute, is studying the use of LCD shutter glasses, like those worn at 3-D movies. The vestibular system, when disturbed, may prevent the retina from holding images steady, thereby inducing nausea. Shutter glasses create a strobe effect that breaks the view into discrete images, fixing each one in one place, which helps the brain coordinate the vestibular with the visual.
For now, a good view is the best way to ease motion sickness. But showing passengers the true movement of the plane can also create problems. In turbulence, a passenger seated at the rear of the plane is moving around in very different ways from the people seated up front. “If you have a clear view,” Planey says, “you can see the fuselage twisting, which is what it’s supposed to do.” But the sight tends to alarm passengers, so designers have learned to interrupt the view through the interiors of most modern jets with restrooms and curtains.
How Much Speed?
What are the real limits for commercial transit on Earth? Assume for a moment that vehicles can travel any route at any speed without tearing apart or running out of gas. Onboard, what can our bodies take?
The longest commercial nonstop flight in the world is Newark to Singapore—a 9,535-mile haul that takes just under 19 hours. Imagine the trip on a maglev train. On a smooth, straight, point-to-point track between the two cities, a commercial maglev operator wanting to avoid passenger complaints would still have to obey conservative, 0.15G limits on acceleration and deceleration. Within those confines, the train would accelerate continuously until, at a halfway point somewhere in the Arctic Circle, it very briefly reached a peak speed of 11,000 mph. Then it would immediately begin a comfortable 0.15G deceleration, for a total trip of just under two hours. If we allowed our theoretical supertrain to follow the more permissive standards of commercial flight, however—1.5 Gs of acceleration, 1 G of deceleration—the journey would be much faster. The train would use the first third of the trip to accelerate to 30,000 mph. Then it would use the remaining two thirds of the trip to (somewhat) gently decelerate. Total time: 46 minutes. All other considerations aside—such as the sonic booms that would deafen the towns along the way—these are the fastest trips any paying, conscious passenger will ever take on this planet.
How close are we to such a trip? In March 2001, Boeing announced its concept for a so-called Sonic Cruiser, capable of flights at just short of the speed of sound—as much as 20 percent faster than the Boeing 747-400, one of the fastest commercial jets in service. The new wide-body plane would, Boeing promised, shave nearly an hour off every 3,000 miles traveled.
Comfort Comes First
But airlines for the most part are finding that it’s easier and cheaper to distract passengers from the experience of travel than it is to make the trip faster and shorter. Passengers are happy to spend a bit of time on the plane, it turns out, if they have a sense of control over their surroundings. “Watching the moving-map display, inflight Internet, television—all of that helps,” Planey says.
Boeing, for its part, is betting that passengers will choose comfort over speed. The company shelved the Sonic Cruiser program in 2002 to focus on the 787 Dreamliner, due to make its first commercial flights next year. The new plane borrows much of the Sonic Cruiser’s structural design; composite materials make up 50 percent of the plane, as compared with 20 percent on the 777.
The flights will be no shorter. But a lighter plane requires less fuel, and, more important, Boeing claims that the composites will make for a more comfortable environment. In a conventional aluminum-fuselage plane, the metal can be corroded by humidity in the cabin, so engineers need to keep the environment extremely dry.
On a pressurized 747, passengers are sitting at the equivalent of 8,000 feet of altitude. In the 787, that perceived altitude can instead be 6,000 feet, and the air will be moister and more pleasant, because the composite materials don’t corrode as quickly. In a Boeing-sponsored Oklahoma State University study, 500 people took a simulated 20-hour flight in the cabin. Passengers reported feeling less achy and more relaxed in the new perceived altitude. Combined with in-flight entertainment and the right lighting, comfort seems to do away with the need for extra speed. If time seems to pass faster, why bother designing a faster plane?
That pilotless Learjet crossed most of the country on its own, and except for the one system needed to keep everyone breathing, the rest of the plane appeared to be functioning flawlessly. The flight couldn’t have been more comfortable, perhaps even for the passengers and crew. The progression of hypoxia—disorientation, sedation, unconsciousness—is often imperceptible to the victim. With a drink or a half-finished latte in their hands, the passengers probably remained in their seats throughout the flight.
The experience of travel gives us the illusion that motion comes at no cost. But vehicles are essentially cocoons, and the systems that cradle us inside them have one fundamental purpose: to keep us from feeling how fast and how far we’ve come.
Directional Materials Could Spawn True One-Way Mirrors and Soundproofing
Nonlinear materials don’t treat all waves equally, but rather respond based on the attributes of the wave passing through it, be it light or sound. By stacking these nonlinear materials asymmetrically in carefully tuned arrangements with other linear materials, it should be possible to create materials that allow a wave traveling in one direction to pass straight through, while virtually repelling an identical wave coming the other way.
That’s the theory anyhow. So far these are only numerical models, and no genuine one-way material has yet been produced. Moreover, the researchers note that no one-way material would be universal--each material would have a range of frequencies and amplitudes for which it would work. For others, it would be less effective.
While that might not have huge implications for cop dramas, it could have a big impact on acoustics. Materials that could be finely tuned to let certain waves pass in only one direction could be used to optimize sound (and light) in novel new ways.
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