Good Reading : February 2011
50 goodreading ı FEBRUARY 2011 by Dr Christopher Smith Can toads predict earthquakes? Why does thinking about food make you eat less? And why does a lap dancer earn bigger tips when she’s at her most fertile? In Stripping Down Science: The naked scientist bares the facts, Dr Chris Smith – founder of the BBC’s multi-award-winning science radio show The Naked Scientists – deploys science in a fascinating and enlightening way to sort fact from fiction and answer questions about all kinds of curly conundrums from everyday life. Here he tells us why you can’t drown in quicksand. There was a time when almost every action movie seemed to involve the hero or villain becoming swamped in quicksand, sinking away until only their hat remained on the surface. Even Flash Gordon and vine-swinging apeman Tarzan were victims during their careers. But contrary to what Hollywood would have you believe, it's actually impossible to drown in quicksand, but almost as impossible to escape, as a Dutch scientist found when he produced his own homemade variety in the laboratory. Daniel Bonn was on holiday in the Iranian province of Qom when he saw a sign saying 'Danger: Quicksand'. Local shepherds had told him that camels and people (usually those who had dared to disagree with the local regime) had periodically disappeared in the area. Realising that science didn't actually have an answer to the quicksand conundrum, he took some samples home with him. Analysis of the composition of the 'quicksand' showed that there are four key ingredients: sand (obviously), water, clay and salt. Together, these materials form a structure resembling a house of cards, with large water- filled gaps between the sand particles, which are loosely glued in place by the clay. As long as it's left alone, the structure remains stable. But as soon as it's disturbed by something stepping on it, the clay changes from a jelly-like consistency to a runny liquid. The effect is the same as stir ring a pot of yoghurt. Liquefying the clay makes the quicksand about one million times runnier, and the whole house of cards comes tumbling down with you inside it. Very quickly, the sand sinks to the bottom and the water floats to the top. This is where the salt comes in.When there's enough salt present, as soon as the clay particles liquefy, electrical charges make them begin to stick together to form bigger particles which also settle in with the sand.The result is a very stodgy layer of sand and clay, twice as dense as the original quicksand and packed tightly around the trapped body parts. So how do you escape? Well certainly not the way Hollywood would have you do it -- by being pulled out by a horse -- because Daniel Bonn's measurements show that the force needed to extract a trapped foot (10,000 newtons) is equivalent to that needed to lift the average family car. You'd probably escape, but minus your legs. The best way out is to try to rebuild the house of cards around the trapped body parts. Making small circles with each part of your body re-introduces water between the sand and clay particles, reducing the density and making it easier for someone to heave you out. Everyone apart from a Hollywood director can take solace from the most important finding of the research: it's impossible to drown in quicksand -- you should only sink halfway. The density of quicksand, at two grams per cubic centimetre, is twice the density of a human (one gram per cubic centimetre). Yet to sink, an object needs to be more dense than the stuff engulfing it, meaning humans, being less dense than quicksand, won't submerge completely and instead become mired at roughly waist height. So stuck you might be, but drowned you wouldn't! Stripping Down Science: The Naked Scientist bares the facts by Dr Christopher Smith is published by Heinemann, r rp $24.95. Stripping Down Science: The Naked Scientist bares the facts BOOKBITE 3 But contrary to what Hollywood would have you believe, it’s actually impossible to drown in quicksand, but almost as impossible to escape ...
December January 2011