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Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address. THE LAST WORD build similar structures around tasty morsels of food. There being no leaves handy in my home, the ants would do me the great favour of collecting up cat hair, lint, pieces of thread and suchlike to construct their little fortresses. They would weave the hairs together very nicely too. They do this in defence of the tasty sweet, and only if the food particle justifies the effort – if it is something they enjoy a good deal, and is too large to be hauled off in just a couple of trips. I watched carefully to see if they seemed to be using the barrier as scaffolding, to make it easier to reach the food and demolish it, but they did not appear to be doing so. This suggests the purpose of the debris is to keep some competitor away from the ants’ prize. I am not sure what competitor this behaviour evolved to thwart, but I can assure you the cat-hair fortresses would have no deterrent effect on my cat, should he decide he wanted their treat. Alyson Irvin Nashville, Tennessee, US No skidding I was watching motorcycle racing at the weekend and noticed that the bikes were taking corners while tilting at well over 45 degrees from the vertical, in fact probably by as much as 60 degrees. Most of the time the bikes managed this without sliding and crashing. How do the bikes lean so steeply and corner on what looks like the side of their tyres without sliding? n Turning a corner, a motorcycle is forced outwards by centrifugal force as well as downwards by the force of gravity. If the turn is taken with bike and rider too upright, centrifugal force flips the bike outwards and throws the rider off. If the bike leans too much, gravity makes it lie down and the tyres lose grip. It then slides out, with the rider usually sliding along behind. With the bike leaning over at the best cornering angle, the combined forces push the mass of the bike out and down through the contact patches where the tyres touch the track. Car tyres only need to work while upright. They have a square cross-section and there is tread only on the crown, not the sides. However, a motorcycle tyre has a rounded cross-section and the tread extends onto the sides of the tyre. This allows the tyres to continue to grip the track, even when the bike leans over in a corner. Richard Whybray Omagh, Tyrone, UK “Leaning pushes the mass of the bike out and down through the patches where the tyres touch the track” Last words past and present, plus questions, at last-word.com The latest collection: witty, brilliant, intelligent and packed with insight Available from booksellers and at www.newscientist.com/elephants Why can’t elephants jump? Ant architects The photo (above) shows a green sweet that has been discovered by ants on a paved path in my garden. The sweet had been dropped several hours before, and had attracted the interest of an ant colony which was carrying it away. But the pattern of the surrounding plant debris is a mystery. What accounts for its arrangement around the candy? n The smaller pieces of debris have been dropped by foraging ants which have discovered the much more valuable sugary sweet on the ground. The larger pieces, leaves and sticks, have been trapped in the moraine of small fragments. John Davies Lancaster, UK n The ants account for the arrangement of leaves around the candy. I know this because I used to watch the ants in my last house “Ants build structures like fortresses around tasty morsels of food in order to defend them” This week’s questions SULTRY NIGHTS A daytime temperature of 20 °C is nice and comfortable, so why is it that if the temperature at night time is 20 °C and you are trying to get to sleep it feels uncomfortably hot, and you spend the night bathed in sweat, pushing the sheets on and off? Craig Mackie London, UK UNMUSICAL SCALE My kettle becomes very noisy when it boils. I live in a hard-water area, so I regularly treat it to remove the build-up of limescale. For a few days it then seems much smoother and quieter. What’s going on? Robert Bull By email, no address supplied PLANE THINKING What is the lowest speed at which a full-size fixed-wing aircraft can fly without stalling? Chris Szymonski Neenah, Wisconsin, US WHICH WAY TO GO? When an arrow is fired from a bow I would expect from Newton’s third law of motion that there should be recoil pushing the bow backwards towards the archer. Yet references appear to contradict this, suggesting the bow wants to follow the arrow. Why? Colin Watters Molesworth, Cambridgeshire
