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Thursday, May 16, 2013
Tuesday, May 14, 2013
The mechanism that puts the curl in the curling stone revealed
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Public release date: 13-May-2013[ | E-mail |
Share ] Contact: Staffan Jacobson
staffan.jacobson@angstrom.uu.se
46-184-713-088
Uppsala University
Researchers from Uppsala University in Sweden can now reveal the mechanism behind the curved path of a curling stone. The discovery by the researchers, who usually study friction and wear in industrial and technical applications, is now published in the scientific journal Wear.
In the curling sport, the players shoot their stones along the ice so that they slowly slide towards the target area, almost 30 m away. The game has its name from the slightly curved "curled" path taken by the stone, when released with a slow rotation. This curled path is important since it is used to reach open spots behind previously played stones, or take out opponent stones behind hindering "guarding" stones. As soon as the player releases the stone, it is only affected by the friction against the ice. The friction can be slightly reduced, and therefore the sliding distance somewhat increased by intensively sweeping the ice just in front of the sliding stone.
If the player gives the stone a clockwise rotation as it is released, it curls to the right, while an anti clockwise rotating stone will curl to the left. The stone is heavy, almost 20 kg, and the rotation is very slow, typically 2-3 rotations during the roughly 25 seconds it takes to slide to the target. This is much too slow to cause the curved path taken by the ball in sports such as table tennis, tennis or soccer.
Despite years of speculations among the curlers and several scientific articles, so far no one has been able to present a good explanation to why the curling stones actually curl; "What puts the curl in the curling stone?". Interestingly, other rotating objects sliding over a surface curl in the opposite direction (make a simple test by sliding for example a glass turned upside down over a slippery floor).
However, the mechanism has now been revealed by researchers at Uppsala University in Sweden. Harald Nyberg, Sara Alfredsson, Sture Hogmark and Staffan Jacobson, who usually study friction and wear in technical and industrial material systems, describe in their article that the curved path is due to the microscopic roughness of the stone producing microscopic scratches in the ice sheet. As the stone slides over the ice the roughness on its leading half will produce small scratches in the ice. The rotation of the stone will give the scratches a slight deviation from the sliding direction. When the rough protrusions on the trailing half shortly pass the same area, they will cross the scratches from the front in a small angle. When crossing these scratches they will have a tendency to follow them. It is this scratch-guiding or track steering mechanism that generate the sideway force necessary to cause the curl.
The importance of having a proper roughness of the sliding surface on the stone to give it he expected trajectory, is since long known among curlers. However, this has not previously been coupled to the steering mechanism. While working on their model the Uppsala researchers experimented with pre-scratching of the ice in various ways, and could then observe that also non-rotating stones could be guided. Stones with very smooth, polished sliding surface were however not affected by the scratches. They also investigated the microscopic scratches made by the stones by moulding replicas of the ice, that were subsequently studied in microscopes.
###
The new results have been published in "The asymmetrical friction mechanism that puts the curl in the curling stone", Nyberg, H., S. Alfredsson, S. Hogmark, and S. Jacobson, Wear (2013), http://dx.doi.org/10.1016/j.wear.2013.01.051
The researchers have also published a validation of older models, showing why they cannot satisfactorily explain the curling mechanisms: H. Nyberg, S. Hogmark, and S. Jacobson, "Calculated trajectories of curling stones sliding under asymmetrical friction - validation of published models". Tribology Letters, on line DOI 10.1007/s11249-013-0135-9, (April 2013)
Read more about the research group: http://www.angstrom.uu.se/tribomaterials
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Public release date: 13-May-2013[ | E-mail |
Share ] Contact: Staffan Jacobson
staffan.jacobson@angstrom.uu.se
46-184-713-088
Uppsala University
Researchers from Uppsala University in Sweden can now reveal the mechanism behind the curved path of a curling stone. The discovery by the researchers, who usually study friction and wear in industrial and technical applications, is now published in the scientific journal Wear.
In the curling sport, the players shoot their stones along the ice so that they slowly slide towards the target area, almost 30 m away. The game has its name from the slightly curved "curled" path taken by the stone, when released with a slow rotation. This curled path is important since it is used to reach open spots behind previously played stones, or take out opponent stones behind hindering "guarding" stones. As soon as the player releases the stone, it is only affected by the friction against the ice. The friction can be slightly reduced, and therefore the sliding distance somewhat increased by intensively sweeping the ice just in front of the sliding stone.
If the player gives the stone a clockwise rotation as it is released, it curls to the right, while an anti clockwise rotating stone will curl to the left. The stone is heavy, almost 20 kg, and the rotation is very slow, typically 2-3 rotations during the roughly 25 seconds it takes to slide to the target. This is much too slow to cause the curved path taken by the ball in sports such as table tennis, tennis or soccer.
Despite years of speculations among the curlers and several scientific articles, so far no one has been able to present a good explanation to why the curling stones actually curl; "What puts the curl in the curling stone?". Interestingly, other rotating objects sliding over a surface curl in the opposite direction (make a simple test by sliding for example a glass turned upside down over a slippery floor).
However, the mechanism has now been revealed by researchers at Uppsala University in Sweden. Harald Nyberg, Sara Alfredsson, Sture Hogmark and Staffan Jacobson, who usually study friction and wear in technical and industrial material systems, describe in their article that the curved path is due to the microscopic roughness of the stone producing microscopic scratches in the ice sheet. As the stone slides over the ice the roughness on its leading half will produce small scratches in the ice. The rotation of the stone will give the scratches a slight deviation from the sliding direction. When the rough protrusions on the trailing half shortly pass the same area, they will cross the scratches from the front in a small angle. When crossing these scratches they will have a tendency to follow them. It is this scratch-guiding or track steering mechanism that generate the sideway force necessary to cause the curl.
The importance of having a proper roughness of the sliding surface on the stone to give it he expected trajectory, is since long known among curlers. However, this has not previously been coupled to the steering mechanism. While working on their model the Uppsala researchers experimented with pre-scratching of the ice in various ways, and could then observe that also non-rotating stones could be guided. Stones with very smooth, polished sliding surface were however not affected by the scratches. They also investigated the microscopic scratches made by the stones by moulding replicas of the ice, that were subsequently studied in microscopes.
###
The new results have been published in "The asymmetrical friction mechanism that puts the curl in the curling stone", Nyberg, H., S. Alfredsson, S. Hogmark, and S. Jacobson, Wear (2013), http://dx.doi.org/10.1016/j.wear.2013.01.051
The researchers have also published a validation of older models, showing why they cannot satisfactorily explain the curling mechanisms: H. Nyberg, S. Hogmark, and S. Jacobson, "Calculated trajectories of curling stones sliding under asymmetrical friction - validation of published models". Tribology Letters, on line DOI 10.1007/s11249-013-0135-9, (April 2013)
Read more about the research group: http://www.angstrom.uu.se/tribomaterials
[ | E-mail | Share ] ?
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.
Source: http://www.eurekalert.org/pub_releases/2013-05/uu-tmt051313.php
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Sunday, May 12, 2013
NASA astronauts fix leak on International Space Station
Astronauts Thomas Marshburn and Christopher Cassidy conducted a spacewalk Saturday to fix an ammonia leak. They replaced a suspected faulty pump on the International Space Station.?
The gloved hands of one of two astronauts working to replace a possible faulty pump on the International Space Station that was leaking ammonia.
NASA screenshot
EnlargeUPDATED: 4:30 p.m., Saturday.
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As a nearly five-hour spacewalk Saturday morning drew to a close, the two astronauts replaced a suspected faulty pump in an effort to fix an ammonia coolant leak on the International Space Station.
Astronauts Thomas Marshburn and Christopher Cassidy began their spacewalk at 8:44 a.m. Saturday. The two successfully replaced a 60-pound pump box which NASA suspected was the source of the leaking ammonia coolant. They found no evidence of the frozen ammonia flakes that had originally led them to the pump box. The astronauts also found no evidence of damage to the pump box.
The walk was hastily planned after ISS crew members alerted Mission Control about the leak on Thursday when they spotted "snowflakes" of frozen ammonia floating near the pump box. NASA says that it has been aware of a slow ammonia leak, but the rate had jump to 5 pounds per day on Thursday.
The ammonia coursing through the plumbing is used to cool the space station's electronic equipment, according to the Associated Press. There are eight of these power channels, and all seven others were operating normally. As a result, life for the six space station residents was pretty much unaffected.
NASA's space station program manager Mike Suffredini said it's a mystery as to why the leak erupted on Thursday. One possibility is a micrometeorite strike.
By 1:20 p.m. Saturday, Cassidy and Marshburn were finished with the space walk, and were heading back to the airlock. They saw no sign of leaks coming from the new pump. NASA engineers continued to pressure check the system and be certain that the new pump is working properly.?
"We're happy, we're very happy [with the space walk]," said Joel Montalbano, Deputy ISS Program Manager, in a press conference in Houston after the space walk. "We didn't see any obvious signs of leaks," but added that testing would continue in the coming days and weeks.
?
If the old pump isn't the source of the leak, NASA's hunt for the source will continue. But that will be another crew's problem. Mashburn and Canadian commander, Chris Hadfield, are scheduled to head back to Earth on Monday.
The two men are experienced space walkers: this was their fourth working sojourn outside the space station. But as they worked, there were the occasional moments when they could pause to look at the view 255 miles above the Earth. "Did you see the moon? Oh my God! Burn that in your memory, said Cassidy.
After running through a system check, the following exchange was heard:
"Houston, if you're still there, I'm feelin great," said Cassidy.
"We're still there. Copy that on feelin great," responded Mike Fincke, an astronaut who was guiding the duo from NASA's Johnson Space Center in Houston.
NASA broadcast the spacewalk live on its website.
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Prince Harry in Colo for wounded vet Warrior Games
COLORADO SPRINGS, Colo. (AP) ? Britain's Prince Harry, a veteran combat helicopter pilot, met Saturday with wounded service members competing in the Paralympic-style Warrior Games in Colorado.
The prince, wearing brown camouflage and boots, met with athletes on the United Kingdom team. He also plans to attend a volleyball match and the opening ceremonies at the Olympic training center in Colorado Springs.
The visit got underway Friday night when Harry charmed dozens of dignitaries, British expatriates, students and military officers at a cocktail party welcoming him to Colorado. He also joined the crowd in singing "Happy Birthday" to U.S. Olympic swimmer Missy Franklin, who was celebrating turning 18 at a golf club south of Denver.
A captain in Britain's Army Air Corps, Harry has deployed to Afghanistan twice. He's attending the Colorado games because he believes the wounded deserve recognition, according to a statement from St. James' Palace in London, the official residence of the royal family.
"He has said before how humbled he feels by the extraordinary courage and fortitude shown by those servicemen and women who have made huge sacrifices for their country, and to whom we all owe a considerable debt of gratitude," the statement said.
Harry returned to Britain in January after a 20-week deployment to Afghanistan as a co-pilot and gunner on an Apache helicopter.
He acknowledged to reporters he had targeted Taliban fighters, and when asked if he had killed anyone, said, "Yeah, so, lots of people have."
His first deployment to Afghanistan, as a forward air controller in 2007-2008, was cut short after 10 weeks when details of his whereabouts were disclosed in the media.
He caused a scandal on his last trip to the U.S. when he was photographed frolicking nude with an unidentified woman in a Las Vegas hotel suite in August.
"It was probably a classic example of me probably being too much army, and not enough prince," he said afterward.
The Warrior Games run through Thursday. They also include basketball, shooting, archery, swimming and track and field. About 260 athletes are expected.
___
Follow Dan Elliott at http://twitter.com/DanElliottAP
Source: http://news.yahoo.com/prince-harry-colo-wounded-vet-warrior-games-160652067.html
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Barns Are Red Because of How Stars Explode
We all know that barns are usually red. But why? Well, the answer is a little more complicated than you might think, but basically it's because of nuclear fusion.
Googler Yonatan Zunger took the time to explain the whole thing in great detail on Google+, and the train of thought goes a little something like this:
- Barns are red because red paint is the cheapest and easiest to make.
- Red paint is the cheapest and easiest to make because the ground is loaded with an iron-oxide compound called red orche. (or basically, rust)
- The ground is loaded with red ochre because when stars die, physics dictates they generate a bunch of iron and explode.
It's that step where things get a little more complicated. Zunger explains it this way:
[When a star dies, it] starts to shrink. And as it shrinks, the pressure goes up, and the temperature goes up, until suddenly it hits a temperature where a new reaction can get started. These new reactions give it a big burst of energy, but start to form heavier elements still, and so the cycle gradually repeats, with the star reacting further and further up the periodic table, producing more and more heavy elements as it goes.
Until it hits 56. At that point, the reactions simply stop producing energy at all; the star shuts down and collapses without stopping. This collapse raises the pressure even more, and sets off various nuclear reactions which will produce even heavier elements, but they don?t produce any energy: just stuff.
This stuff-generation just continues for a while, churning out material with an atomic mass of around 56 (iron) until eventually, it meets its final demise and explodes (sometimes), seeding that material through out the cosmos.
It's that rusty startdust that litters the ground of this planet we live on and makes it cheap and easy to get a whole bunch of red paint for our barns. Crazy, right? You can dig waaaaaay deeper into the nitty gritty details by reading Zunger's wildly in-depth post. [Yonatan Zunger via Smithsonian Blog]
Image by MaxyM/Shutterstock
Source: http://gizmodo.com/barns-are-red-because-of-how-stars-explode-501906503
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