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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 Watermelon weirdness What caused the oddly attractive patterns on the skin of this watermelon (see photo)? It was grown and purchased on one of the Canary Islands. n The patterns are caused by papaya ringspot virus type-W, which despite its name only infects plants such as watermelon, cucumber and courgettes. While it can stunt growth and reduce yield, the patterns on the skin are, as you say, attractive, and in some parts of the world they sell for higher prices. The virus is classified as a potyvirus and like most plant viruses has a single- stranded RNA genome. Meriel Jones Port Sunlight, Merseyside, UK Pooling resources When I open a new jar of marmalade the contents are a nice, semi-solid, homogenous mass with a smooth surface, however old the jar is. Yet when I make a spoonful-sized hole in the flat surface to remove some marmalade, the next time I open the jar a couple of days later, the hole has started to fill with a syrupy liquid. What is it about breaking the surface of the marmalade that sets this process in motion? It continues until the jar is empty. n A proper marmalade contains plenty of pectin, which is fluid while the product is still hot from cooking, but forms a gel as it cools. The gel is a sponge of chain-like pectin molecules in a liquid syrup. The sponge neatly fills the jar as you open it and the syrup neatly fills the sponge, simply because the sponge formed from molecules dispersed evenly through the syrup. If you were to skim your marmalade from the top instead of digging great, vulgar holes in it, the marmalade would remain intact. But if you tear gaps into the delicate structure, quarrying it, then the fluid syrup from the higher levels of sponge will seep down into the hollows. You might feel guilty though when you remember how forgivingly, selflessly, marmalade turns the other cheek, melting obligingly on hot buttered toast. But don’t trust its treacherous meekness! Lumps bide their time to topple onto your best shirt, smearing elbow, table and floor. And in hotels it will humiliate you in the eyes of guests, hosts, clients or colleagues. Can’t find that report? What is that sticking to the seat of your trousers? Jon Richfield Somerset West, South Africa Revision tactics Is it better to stay up late on the night before an exam, learning those last-minute facts, or to get up early and revise in the morning before the exam? n For 40 years, I have told my students that, the day before their exam they should pack some sandwiches and a can of drink, and go for walk in a high and windy place, with a friend. Forget all the exam tension, ensure that they are fit, and give all the knowledge they have acquired time to sort itself out. Yet when I come in on an exam morning about 7am to check on everything, I invariably find all the students sprawled over the stairs, red-eyed and yawning, in a cloud of (illegal) cigarette smoke, poring over their notebooks. Some of them have been there almost all night. I can’t think of a better way to reduce your efficiency, and indeed some fall asleep during the exam. If you must revise at the last minute, the evening before would be better, so that you will be fresh in the morning. John Anderson Warsaw, Poland n Neither. It’s too late by then. If you don’t know it by the night before the exam, there’s nothing you can do apart from try to relax a bit and rely on all the hard work you’ve done before. (You have done all the work before, I hope) Gail Volans Brean, Somerset, UK This week’s question FOUR BOB GOOD Why are four-person bobsleighs faster than two-person bobsleighs? Is it because they have two extra people pushing at the start and therefore are faster throughout their run or is it to do with weight and momentum? Surely there comes a point when the extra weight slows the bob too much? A few friends and I spent an hour or so arguing over this the other week, divided into those who thought it was the extra weight and others who thought it was the extra runners. Alan Kane Glasgow, UK Last words past and present, plus questions, at www.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?
