- Email: [email protected]
Bubble shapes
The last word– BUBBLE SHAPES I was washing the dishes when I noticed that the bubbles in a splodge of soapy water on the counter had a very regular structure. The bubbles, all small and identical in size, had arranged themselves in patches of hexagonal lattices, very like a single sheet of graphite. Even when individual bubbles burst, the lattices held their shape. The bubbles did not touch as there was water between them, so how did this structure come about? (Continued)
As an addendum to your earlier answer on bubble shapes, readers may like to know that floating rafts of soap bubbles on a dish of water were used by Nobel prize-winning physicist Lawrence Bragg and colleague John Nye in 1947 to simulate the packing of atoms in metallic crystals. Defects caused by missing atoms were simulated by simply popping one of the bubbles. Len Fisher Bradford-on-Avon, Wiltshire, UK
SHIFTING SANDS How deep is the sand of the Sahara desert and what is directly beneath it? The Sahara is subject to considerable wind erosion and its sand is found thousands of miles away. Is it replenished by some means?
any reason, more is likely to collect in the same place. Sand accordingly forms wind-driven dunes, whose behaviour is astonishingly complex. Surface sand seldom piles higher than a couple of hundred metres above underlying earth or bedrock, except by filling ancient valleys or lakes. Such deep sands and spongy sandstone form important groundwater reservoirs. And yes, sand does form and re-form constantly as water erosion, frost and wind-driven particles flake grains off rocks. Conversely, deep moist layers of sand become cemented into sandstone, which in turn may go through the same cycle after millions of years. Far deeper sand occurs in submarine detritus fans which build up at the mouths of rivers. Even more intriguingly, the Mediterranean has dried up repeatedly in the last tens of millions of years. Each time that happened, rivers flowing into the basin eroded their fans into massive canyons, which silted up again whenever the sea returned. The bed of the lower reaches of the Nile consists of silt, more or less compacted, kilometres deep, turning it into an underworld canyon that has dwarfed the Grand Canyon in the past. Jon Richfield Somerset West, South Africa
Not all the Sahara is sandy, but wherever wind-blown sand settles for
At more than 9 million square kilometres, the Sahara is the world’s largest desert but it has no uniform topography. About 15 per cent of the area is covered by sand dunes, 70 per cent is made up of stone deserts of denuded rock and coarse gravel, while the rest is oases and mountain ranges. Beneath the sand dunes lies rock of
Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and a fax if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all answers that are published will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted
by readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280) or by email to [email protected] (all correspondents should include their postal address in order to receive payment for answers). If you would like a complete list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? As part of our 50th anniversary we have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
Last Words past and present, plus a full list of unanswered questions, are available on New Scientist’s website at www.newscientist.com
varying types. In Algeria and Libya, deposits of oil and gas have also been discovered, although inaccessibility has hampered their exploitation. The same forces that remove sand from the Sahara are also largely responsible for it being replenished. The wind not only sweeps sand from one area, but causes erosion of rocks in others which leads to it being replaced. Ian Smith London, UK
THIS WEEK’S QUESTIONS Beach life On holiday on the Dingle peninsula, south-west Ireland, this summer I spotted a sea creature I had never seen before. There were large numbers of them on the beach. I showed my photograph (above) to a boatman and he thought maybe they were related to the goose barnacle. Can any reader offer a positive identification and a
description of the creature’s life cycle? Girish Patel Wirral, Merseyside, UK Wakey wakey Why is it when we are tired the blood vessels in our eyes are more visible? Lucy Bennett By email, no address supplied Bovine challenge How long would it take an average cow to fill the Grand Canyon with milk? Nicola Stanley Cambridge, UK Loud shirt I recently appeared on my local TV station. When I arrived at the studio I was asked to change my shirt because its pattern would look distorted on screen. What causes this effect and why, in this day and age, is it impossible for television to simply record what is in front of the cameras? Alan Francis Cardiff, UK
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions
Available in bookstores and online
As an addendum to your earlier answer on bubble shapes, readers may like to know that floating rafts of soap bubbles on a dish of water were used by Nobel prize-winning physicist Lawrence Bragg and colleague John Nye in 1947 to simulate the packing of atoms in metallic crystals. Defects caused by missing atoms were simulated by simply popping one of the bubbles. Len Fisher Bradford-on-Avon, Wiltshire, UK
SHIFTING SANDS How deep is the sand of the Sahara desert and what is directly beneath it? The Sahara is subject to considerable wind erosion and its sand is found thousands of miles away. Is it replenished by some means?
any reason, more is likely to collect in the same place. Sand accordingly forms wind-driven dunes, whose behaviour is astonishingly complex. Surface sand seldom piles higher than a couple of hundred metres above underlying earth or bedrock, except by filling ancient valleys or lakes. Such deep sands and spongy sandstone form important groundwater reservoirs. And yes, sand does form and re-form constantly as water erosion, frost and wind-driven particles flake grains off rocks. Conversely, deep moist layers of sand become cemented into sandstone, which in turn may go through the same cycle after millions of years. Far deeper sand occurs in submarine detritus fans which build up at the mouths of rivers. Even more intriguingly, the Mediterranean has dried up repeatedly in the last tens of millions of years. Each time that happened, rivers flowing into the basin eroded their fans into massive canyons, which silted up again whenever the sea returned. The bed of the lower reaches of the Nile consists of silt, more or less compacted, kilometres deep, turning it into an underworld canyon that has dwarfed the Grand Canyon in the past. Jon Richfield Somerset West, South Africa
Not all the Sahara is sandy, but wherever wind-blown sand settles for
At more than 9 million square kilometres, the Sahara is the world’s largest desert but it has no uniform topography. About 15 per cent of the area is covered by sand dunes, 70 per cent is made up of stone deserts of denuded rock and coarse gravel, while the rest is oases and mountain ranges. Beneath the sand dunes lies rock of
Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and a fax if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all answers that are published will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted
by readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280) or by email to [email protected] (all correspondents should include their postal address in order to receive payment for answers). If you would like a complete list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? As part of our 50th anniversary we have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
Last Words past and present, plus a full list of unanswered questions, are available on New Scientist’s website at www.newscientist.com
varying types. In Algeria and Libya, deposits of oil and gas have also been discovered, although inaccessibility has hampered their exploitation. The same forces that remove sand from the Sahara are also largely responsible for it being replenished. The wind not only sweeps sand from one area, but causes erosion of rocks in others which leads to it being replaced. Ian Smith London, UK
THIS WEEK’S QUESTIONS Beach life On holiday on the Dingle peninsula, south-west Ireland, this summer I spotted a sea creature I had never seen before. There were large numbers of them on the beach. I showed my photograph (above) to a boatman and he thought maybe they were related to the goose barnacle. Can any reader offer a positive identification and a
description of the creature’s life cycle? Girish Patel Wirral, Merseyside, UK Wakey wakey Why is it when we are tired the blood vessels in our eyes are more visible? Lucy Bennett By email, no address supplied Bovine challenge How long would it take an average cow to fill the Grand Canyon with milk? Nicola Stanley Cambridge, UK Loud shirt I recently appeared on my local TV station. When I arrived at the studio I was asked to change my shirt because its pattern would look distorted on screen. What causes this effect and why, in this day and age, is it impossible for television to simply record what is in front of the cameras? Alan Francis Cardiff, UK
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions
Available in bookstores and online