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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 Wet, wet, dry Please help settle an argument. In winter we have to dry our washed clothes on our house radiators. However, there are too many items of laundry in one wash for them all to fit on the radiators, so some have to wait their turn on clothes horses at room temperature. My wife says we should put all the small, quickly drying items such as socks, underwear and synthetic sports gear on the radiators first because these will dry much faster than jeans, jumpers and heavy linen items. I argue that the order they are placed and removed from the radiator makes no difference to the total drying time of all the items. My wife says the total drying time is faster if you dry the small items first and then the heavy items. Who is right? Thanks to the many people who answered this question. Sadly the disagreement between our correspondent and his wife persists in those answers, as the following selection demonstrates. Where are the experimentalists when you need them? – Ed n Let’s say we have washed some nylon underwear and cotton T-shirts. We’ll assume the nylon dries in 1 hour on the radiator and the T-shirts take 5 hours. (The exact time will depend on the room’s temperature and humidity.) If you put the nylon items on the radiator first, you will be able to put them away in 1 hour, then put the T-shirts on the radiator and get rid of the clothes horse. If you start with the T-shirts on the radiator, the nylon items will have to sit on the clothes horse for 5 hours. So it is a good idea to start with the fast-drying items. It might not be faster but is certainly more convenient. To answer the question directly, the total drying time should be the same no matter which clothes you put on the radiator first. Tristana Simon Seaford, Victoria, Australia n We can assume that the heavy items such as jeans would take 36 hours to dry at room temperature, while socks take only 18 hours. Let’s also assume that items on the radiator dry in one-sixth of the time they need at room temperature, and that we are only washing jeans and socks. If jeans are placed first on the radiator they will dry in 6 hours. The socks will then be dry in another 12 hours at room temperature, or 2 hours on the radiator. The total drying time is thus 8 hours. If socks go on the radiator first then they will be dry in 3 hours, leaving 5.5 hours for the jeans. In this case the total drying time is 8.5 hours. If you add a third type of garment – say cardigans that take 24 hours to dry at room temperature – then the sequence of jeans, then cardigans, then socks on the radiator yields a total time of 10.5 hours. The reverse sequence would take 11.4 hours. So it would seem that both the questioner and his wife are incorrect. My solution? Buy a tumble dryer. Matthew Shepherd Banbury, Oxfordshire, UK n Drying time is the same, but the amount of time spent on the clothes horse is reduced if you do the quick-drying ones first. But why are you drying clothes on heated surfaces at all? It can damage the plastic bits such as fasteners in modern clothing, nylon fabrics, and more. Buy some fold-away drying racks and wash your clothes in cold water, and you’ll notice their colours will stay brighter for longer. But if you value your marriage, then the answer to the question is that your spouse is right. Give in on the inconsequential things and you’ll have a better shot at winning when it really matters. Liz Zitzow No address supplied Whistle-stop I recently bought a roof rack for my car and to my delight discovered it likes to whistle when my car approaches 100 kilometres per hour. But why does the whistling stop whenever I go under a bridge? n To produce a noise, the roof rack needs to be struck at a suitable angle by a sufficiently strong, stable wind. The same effect comes into play when you blow across the mouth of a bottle. Taut strings also do interesting things in winds at various angles. When your car travels at speed in an open space, a stable slipstream develops, which sustains your roof rack’s whistle. A bridge, especially one without much space beneath, disrupts this flow around your car and redirects the wind. If this changes the angle at which the slipstream meets the rack then the whistle stops, at least temporarily. To pin down this behaviour, you can easily experiment with roof racks of different sizes and shapes and drive your car in a range of environments. To fresh winds and bridges new. Jon Richfield Somerset West, South Africa This week’s question ON THE BOUNCE The schoolchildren I teach are investigating how different types of balls bounce. We noticed that tennis balls are filled with gas to keep them firm. What would happen if they were filled with helium? Would they bounce higher, or even float like party balloons? How would table-tennis balls or footballs behave if filled with helium? Dr Gitsham and class 7S3 Saffron Walden County High School Essex, UK “If you value your marriage, then the answer to the question is that your spouse is right” Last words past and present, plus questions, at last-word.com A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans Why are orangutans orange?
