Posted on 12/17/2004, 3:50:52 AM by neverdem
Courtesy of Dr. Detlef Lohse/Nature
Snapshots show a weighted Ping-Pong ball sinking into dry quicksand. The 4.7-ounce ball disappears in about one-tenth of a second and then expels a narrow jet of sand.
Beware of playing in any sandboxes you might find in the laboratory of Dr. Detlef Lohse.
Traditional deathtrap quicksand is a slurry of sand, water and clay. The water keeps the sand from sticking together to support weight, and a person who steps in slowly sinks.
Now Dr. Lohse, a professor of applied physics, and his colleagues at the University of Twente in the Netherlands show that it is possible to vanish into a pile of completely dry sand as well. Worse, their sand looks the same as the normal, weight-supporting variety.
In the current issue of the journal Nature, the researchers describe their experiment. They puffed air through fine-grained sand, shuffling the grains of sand into a more precarious arrangement - something like a house of cards. Even after the air was turned off and the sand settled, the packing density of the grains was an airy 41 percent, down from 60 percent initially.
The researchers suspended a Ping-Pong ball, weighed down with bits of bronze, so that it just touched the surface of the sand. They then burned the string holding the doomed ball. The fluffy sand was incapable of supporting the ball, which immediately and quickly sank without a splash.
A tenth of a second later, the backwash of sand closing up behind the sinking ball caused a thin narrow jet of sand to shoot several inches into the air, like a desperate distress call. Heavier balls sank deeper into the sand, and the jets occurred only for those weighing more than an ounce.
Dr. Lohse said the findings could explain reports of travelers' being swallowed up in the desert.
"The U.S. Army is very interested in this," he said, "because these days, the U.S. Army tends to go to desert states."
That's it. I'm staying at the pool.
I'm with you!
While I love the beach...only in winter, when I can bring the dogs down, and feel the salt of the sea-spray on my face.
For relaxation? Give me a sun-lounger and a pool!
I hate it when fine sand gets into the crevices that your crevices didn't even know existed!
But can it be created in the natural world? I always wondered about those scenes in Lawrence of Arabia and Mad Max: Beyond Thunderdrome where a boy sinks into desert quicksand - over his head - not floating like you might in wet quicksand.
The same thing happens with water. If the earth is venting a large volume of gas down on the seabed, the water above is full of bubbles and thus much less dense than normal water. It is theorized that this phenomenon has been responsible for a number of ship disappearances.
As for this experiment I could of told them what would happen. I used to play with microballoons all the time in the layup room. You could get an almost liquid like behavior by blowing bursts of air into a package of the stuff.
Nice to know that I'm not the only MythBuster fan here at FR!
One of the few shows on TV I actually watch.
Is that a polite was of saying that when the Earth farts, it will blow a ship to hell?
Boy, these people must be really bored.
IIRC, there are reports of eruptions of different gases all over the natural world. How about some natural gas in the mideast under the sands of the desert? Wasn't there a report of hydrogen sulfide gas emission/eruption below a lake in Africa that killed scores of people living around the lake?
FReepmail me if you want on or off my health and science ping list.
More like an Earth fart really sucks -- sucks ya down to Davy Jones locker.
Sound waves, or more accurately the vibrations they create, can also affect the density of solids like sand, rock, snowpack. It's probably the reason why landslides and avalanches travel much further than they theoretically should.
Camaroon, I think.
Thomas Jefferson writing in in the late 1700s/early 1800s in Notes on the State of Virginia described two natural gas vents covered with sand in Virginia which he called "burning springs."
In the low grounds of the Great Kanhaway, 7 miles above the mouth of Elk river, and 67 above that of the Kanhaway itself, is a hole in the earth of the capacity of 30 or 40 gallons, from which issues constantly a bituminous vapour in so strong a current, as to give to the sand about its orifice the motion which it has in a boiling spring. On presenting a lighted candle or torch within 18 inches of the hole, it flames up in a column of 18 inches diameter, and four or five feet height, which sometimes burns out within 20 minutes, and at other times has been known to continue three days, and then has been left still burning. The flame is unsteady, of the density of that of burning spirits, and smells like burning pit coal. Water sometimes collects in the bason, which is remarkably cold, and is kept in ebullition by the vapour issuing through it. If the vapour be fired in that state, the water soon becomes so warm that the hand cannot bear it, and evaporates wholly in a short time. This, with the circumjacent lands, is the property of his Excellency General Washington and of General Lewis.There is a similar one on Sandy river, the flame of which is a column of about 12 inches diameter, and 3 feet high. General Clarke, who informs me of it, kindled the vapour, stayed about an hour, and left it burning.
Happens regularly with canoers and kayakers. Water can be so white that it will not float a boat.
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