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Iron plants
THE LAST WORD The big chill Since my retirement I often succumb to an afternoon nap on the nearest couch. I am perfectly comfortable when I drift off and the temperature in my house is thermostatically controlled, yet I frequently wake up with a bone-deep chill. In the interest of helping baby boomers enjoy their future retirement, what is going on?
Last words past and present, plus questions, at last-word.com
normal activities – apart from the cost to your purse and the environment. It’s probably best to cover yourself with a blanket. Hands and feet play a special role in normal moment-tomoment temperature regulation. When you are at thermal equilibrium with your surroundings, blood in the vessels of the hands will keep them warm. The warmest skin temperature in a warm person is in the fingers. This is due to small but effective heat-exchanging blood vessels in the extremities of warm-blooded animals, the arteriovenous anastomoses. These supply the
n When you lie down to nap, your heat production will drop to a resting value. When you fall asleep, your metabolism will drop further to around 80 per cent of that resting value. The body tries “The warmest skin to balance heat production with temperature in a person heat loss to maintain thermal who is already warm is equilibrium, so during your nap found in their fingers” body temperature will fall and you will feel cold. During the day, heat balance of superficial veins of the forearms the body will be upheld as a result and legs with warm arterial blood, of its normal thermoregulation. keeping the underlying muscles So when it gets cooler, your body warm and effective, so the animal will react by an involuntary or person is instantly ready for increase in muscular activity, and fight or flight. They also serve as you might even start shivering if regulators of heat dissipation the drop is too sudden. During from the body. sleep these normal In sleep, this mechanism is also thermoregulatory mechanisms active, making a good and react more sluggishly and that is refreshing sleep difficult to obtain the reason why you wake up cold. if your hands are cold. My mother This has nothing to do with age, taught me always to cover myself but is due to a combination of with a blanket if I was to take a how tired you are and the room nap, and to tug the hands of her temperature. You could raise the grandchildren down under the room temperature to a level cover if they were to fall asleep. where your body would be at Leif Vanggaard thermal equilibrium during sleep, Retired surgeon-captain but this would be uncomfortable Danish Arctic Institute when you later went about your Hellerup, Denmark
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.
Plane thinking What is the lowest speed at which a full-size fixed-wing aircraft can fly without stalling?
n Even when an aircraft is in straight level flight, it is not horizontal. There is an “angle of attack” between the longitudinal axis (the gangway) of the aircraft and the airflow, so the leading edge of each wing is higher than the trailing edge. This means that the air is deflected downwards – resulting in a reactive force with an upward component (lift) and a backward component (drag). Forward motion is needed to generate lift. The faster the aircraft is travelling, the smaller the angle of attack needed to generate the lift which is required to counter the aircraft’s weight. As the aircraft slows down, the required angle of attack must increase to maintain lift. But increasing the angle of attack also increases drag, which slows the aircraft further, reducing lift. The stall speed is the speed at which increasing the angle of attack can no longer be used to generate lift, so the aircraft descends. Stall speed is slowest when the aircraft is in straight level flight. When an aircraft turns it has to bank and so generates less lift, leading to an increase in stall speed. Increasing the payload or pulling up from a dive also increases stall speed, as does increasing the drag when the aircraft is in a landing configuration with its
undercarriage down. For example, the stall speed of a Boeing 737 in straight level flight is about 220 kilometres per hour, compared with about 295 kilometres per hour when coming in to land. Air France 447 tragically crashed into the Atlantic on 1 June 2009. Even though all components of the data flight recorder were recovered on 2 May this year, the crash remains unexplained. It is thought that icing of the pitot tubes, which calculate airspeed from the pressure of the outside air flow, generated erroneous airspeed data. According to a report published on 27 May by the French Bureau of Enquiry and Analysis for Civil Aviation Safety, this led the pilot to increase the angle of attack, stalling the aircraft. The mystery is that the aircraft stayed in a stall throughout the 3.5 minutes of descent from an altitude of 38,000 feet, with an angle of attack consistently around 35 degrees. Without the benefit of daylight the crew had to rely on instruments in which they appear to have lost faith. Mike Follows Willenhall, West Midlands, UK
This week’s question Iron plants
Iron deficiency is common among human vegetarians, so how do herbivores cope? Melanie Green Hemel Hempstead, Hertfordshire, UK
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans
Last words past and present, plus questions, at last-word.com
normal activities – apart from the cost to your purse and the environment. It’s probably best to cover yourself with a blanket. Hands and feet play a special role in normal moment-tomoment temperature regulation. When you are at thermal equilibrium with your surroundings, blood in the vessels of the hands will keep them warm. The warmest skin temperature in a warm person is in the fingers. This is due to small but effective heat-exchanging blood vessels in the extremities of warm-blooded animals, the arteriovenous anastomoses. These supply the
n When you lie down to nap, your heat production will drop to a resting value. When you fall asleep, your metabolism will drop further to around 80 per cent of that resting value. The body tries “The warmest skin to balance heat production with temperature in a person heat loss to maintain thermal who is already warm is equilibrium, so during your nap found in their fingers” body temperature will fall and you will feel cold. During the day, heat balance of superficial veins of the forearms the body will be upheld as a result and legs with warm arterial blood, of its normal thermoregulation. keeping the underlying muscles So when it gets cooler, your body warm and effective, so the animal will react by an involuntary or person is instantly ready for increase in muscular activity, and fight or flight. They also serve as you might even start shivering if regulators of heat dissipation the drop is too sudden. During from the body. sleep these normal In sleep, this mechanism is also thermoregulatory mechanisms active, making a good and react more sluggishly and that is refreshing sleep difficult to obtain the reason why you wake up cold. if your hands are cold. My mother This has nothing to do with age, taught me always to cover myself but is due to a combination of with a blanket if I was to take a how tired you are and the room nap, and to tug the hands of her temperature. You could raise the grandchildren down under the room temperature to a level cover if they were to fall asleep. where your body would be at Leif Vanggaard thermal equilibrium during sleep, Retired surgeon-captain but this would be uncomfortable Danish Arctic Institute when you later went about your Hellerup, Denmark
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.
Plane thinking What is the lowest speed at which a full-size fixed-wing aircraft can fly without stalling?
n Even when an aircraft is in straight level flight, it is not horizontal. There is an “angle of attack” between the longitudinal axis (the gangway) of the aircraft and the airflow, so the leading edge of each wing is higher than the trailing edge. This means that the air is deflected downwards – resulting in a reactive force with an upward component (lift) and a backward component (drag). Forward motion is needed to generate lift. The faster the aircraft is travelling, the smaller the angle of attack needed to generate the lift which is required to counter the aircraft’s weight. As the aircraft slows down, the required angle of attack must increase to maintain lift. But increasing the angle of attack also increases drag, which slows the aircraft further, reducing lift. The stall speed is the speed at which increasing the angle of attack can no longer be used to generate lift, so the aircraft descends. Stall speed is slowest when the aircraft is in straight level flight. When an aircraft turns it has to bank and so generates less lift, leading to an increase in stall speed. Increasing the payload or pulling up from a dive also increases stall speed, as does increasing the drag when the aircraft is in a landing configuration with its
undercarriage down. For example, the stall speed of a Boeing 737 in straight level flight is about 220 kilometres per hour, compared with about 295 kilometres per hour when coming in to land. Air France 447 tragically crashed into the Atlantic on 1 June 2009. Even though all components of the data flight recorder were recovered on 2 May this year, the crash remains unexplained. It is thought that icing of the pitot tubes, which calculate airspeed from the pressure of the outside air flow, generated erroneous airspeed data. According to a report published on 27 May by the French Bureau of Enquiry and Analysis for Civil Aviation Safety, this led the pilot to increase the angle of attack, stalling the aircraft. The mystery is that the aircraft stayed in a stall throughout the 3.5 minutes of descent from an altitude of 38,000 feet, with an angle of attack consistently around 35 degrees. Without the benefit of daylight the crew had to rely on instruments in which they appear to have lost faith. Mike Follows Willenhall, West Midlands, UK
This week’s question Iron plants
Iron deficiency is common among human vegetarians, so how do herbivores cope? Melanie Green Hemel Hempstead, Hertfordshire, UK
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans