Meredith, Calum James, David Boulderstone, and Simon Clapton (2011). ‘Association Football on Mars.’ Journal of Physics Special Topics 9 (1).
–– (2010). ‘None Like It Hot.’ Journal of Physics Special Topics 9 (1).
–– (2010). ‘None Like It Hot II.’ Journal of Physics Special Topics 9 (1).
Basic Black Dress: Hot or Not?
Why do Bedouins wear black robes in hot deserts? The question so intrigued four scientists – all non-Bedouins – that they ran an experiment. Their study, called ‘Why Do Bedouins Wear Black Robes in Hot Deserts?’, was published in the journal Nature in 1980.
‘It seems likely’, the scientists wrote, ‘that the present inhabitants of the Sinai, the Bedouins, would have optimised their solutions for desert survival during their long tenure in this desert. Yet, one may have doubts on first encountering Bedouins wearing black robes and herding black goats. We have therefore investigated whether black robes help the Bedouins to minimise solar heat loads in a hot desert.’
The research team – C. Richard Taylor and Virginia Finch of Harvard University, and Amiram Shkolnik and Arieh Borut of Tel Aviv University – quickly discovered that, as you might suspect, a black robe does convey more heat inward than a white robe does. But they doubted that this was the whole story.
They found inspiration and guidance in a 1969 report about cattle. John Hutchinson and Graham Brown of the Ian Clunies Ross Animal Research Laboratory, in Prospect, New South Wales, Australia, worked with Friesian dairy cows. The Australian team discovered that light and heat penetrate deeper into white cattle hair than into black. The saving grace for cattle is that even a tiny amount of wind whisks away that extra heat.
However, cattle are not people. So, what of man (and woman)?
Taylor, Finch, Shkolnik, and Borut measured the overall heat gain and loss suffered by a brave volunteer. They described the volunteer as ‘a man standing facing the Sun in the desert at mid-day while he wore: (1) a black Bedouin robe; (2) a similar robe that was white; (3) a tan army uniform; and (4) shorts (that is, he was semi-nude)’.
Each of the test sessions (black-robed, white-robed, uniformed, and half-naked) lasted thirty minutes. It was hot there in the Negev Desert at the bottom of the rift valley between the Dead Sea and the Gulf of Elat. The volunteer stood in temperatures that ranged from a just-semi-sultry 35 degrees Celsius (95 degrees Fahrenheit) to a character-building 46 degrees Celsius (115 degrees Fahrenheit). Though he is now nameless, this was his day in the sun.
The results were clear. As the report puts it: ‘The amount of heat gained by a Bedouin exposed to the hot desert is the same whether he wears a black or a white robe. The additional heat absorbed by the black robe was lost before it reached the skin.’
Bedouins’ robes, the scientists noted, are worn loose. Inside, the cooling happens by convection – either through a bellows action, as the robes flow in the wind, or by a chimney sort of effect, as air rises between robe and skin.
Thus it was conclusively demonstrated that, at least for Bedouin robes, black is as cool as any other colour.
Shkolnik, Amiram, C. Richard Taylor, Virginia Finch, and Arieh Borut (1980). ‘Why Do Bedouins Wear Black Robes in Hot Deserts?’ Nature 283: 373–75.
Hutchinson, John C. D., and Graham D. Brown (1969). ‘Penetrance of Cattle Coats by Radiation.’ Journal of Applied Physiology 26 (4): 454–64.
Capacity of the Nose
‘What is the Air-Conditioning Capacity of the Human Nose?’ Spring this question the next time you find yourself at a party where everybody else is an HVAC engineer. HVAC engineers specialize in heating, ventilating, and air conditioning. But, as a group, HVAC engineers are surprisingly ignorant about the air-conditioning capacity of their own noses.
Your question might throw the engineers into a two-part frenzy: first measuring each other’s nasal cavity dimensions, temperatures, and vapour concentrations; and then competitively calculating, calculating, calculating until the party ends.
You could save them the trouble. Tell them about a report called ‘The Air-Conditioning Capacity of the Human Nose’, which was published in the Annals of Biomedical Engineering. There, Sara Naftali and her colleagues at Tel Aviv University tell how they attacked the question by using three artificial noses.
None of these artificial noses are ones that a mother would love if she saw one installed on her child. The first, which the scientists call ‘nose-like’, would seem anything but if it were mounted on someone’s face. This rough-hewn product of a machine shop has internal ductwork that corresponds to ‘averaged data of human nasal cavities’. A later version is called, unappealingly, ‘nose-like with valve’.
The third artificial nose is a mechanically detailed reproduction of one individual’s nose, with lots of twisty, bumpy idiosyncrasies. Because this nose – like most noses – is far from average, the scientists used it mostly in a sort of ‘reality check’ to compare against the performance of the nose-like nose and the nose-like with valve.
The ensuing artificial huffing and puffing taught them two things. First, that the nose-like noses behave realistically enough for scientists not to have to do too many uncomfortable experiments using actual people’s actual noses. And second, that the basic ductwork appears to handle ninety percent or so of a person’s air-conditioning needs – it delivers air of usable temperature and humidity to the lungs no matter how cold, hot, humid, or dry the atmosphere happens to be.
Now, should you happen to be introduced to one of the very few party-going HVAC engineers who does know the air-conditioning capacity of the human nose, do not despair. You can still stimulate a good conversation. Simply ask: what is the cooling power of the pigeon head?
For years, birders disagreed as to how their favourite animals manage to keep from overheating. More than a decade ago, Robert St. Laurent and Jacques Larochelle of the Université Laval in Quebec, Canada, wrote ‘The Cooling Power of the Pigeon Head’. It describes how they inserted electronic temperature probes, via the rear exhaust openings, up into the intestines of several birds; then body-wrapped the birds; then put them into a wind tunnel.
They discovered that simply opening one’s beak, without making a sound, is sufficient to keep things from getting overheated. It remains for others to see if this applies to partygoers in conversation, as well as to birds in flight.
Naftali, Sara, Moshe Rosenfeld, Michael Wolf, and David Elad (2005). ‘The Air-Conditioning Capacity of the Human Nose.’ Annals of Biomedical Engineering 33 (4): 545–53.
St. Laurent, Robert, and Jacques Larochelle (1994). ‘The Cooling Power of the Pigeon Head.’ Journal of Experimental Biology 194: 329–39.
Moving Violations
Historically, Europe’s washing machines tended to walk across a room, while America’s did not. Daniel Conrad and Werner Soedel explained why, in a study called ‘On the Problem of Oscillatory Walk of Automatic Washing Machines’. Conrad and Soedel, based at the School of Mechanical Engineering at Purdue University in West Lafayette, Indiana, published their work in 1995 in the Journal of Sound and Vibration. Their explanation has been recognized by authority figures for its power to inspire youths.
The fear of ambling machinery resonated with modern times. One could feel it in the 1995 Japanese science-fiction film Mechanical Violator Hakaider. Critic Jason Buchanan later described what happens once the title character, a cyborg, is loosed upon the land: ‘Once Hakaider sets on the path of destruction there is little that can be done to stop him from destroying all of Jesus Town.’
Washing machines of that era sometimes contained frightful things. A 1993 detective thriller called Vortice Mortale (English title: The Washing Machine) cinematically depicted a dismembered man inside an Italian unit.
Conrad and Soedel eschewed the sensational, restricting themselves to the engineering basics. ‘The problem of walk in automatic washing machines is becoming more and more of interest to appliance manufacturers’, they wrote. ‘The current tr
end is towards lightweight plastic and composite components. The reduction of mass associated with these changes in materials increases the possibility that a washing machine will walk.’
In washing machines, the propensity to waddle is the consequence of a particular design choice. While steadfast American machines rotated their dirty clothes about a vertical axis, European designs typically made the internal machinery twirl around horizontally.
Conrad and Soedel saw this as a mechanical and business blunder. They wrote: ‘The horizontal axis washer has innate unbalance problems associated with the design. This unbalance can typically create a force in excess of 19 kilonewtons during the spin cycle.’
Four years after the publication of ‘On the Problem of Oscillatory Walk of Automatic Washing Machines’, two officers at the US Military Academy in West Point, New York, used it as a major source for their paper ‘Basic Vibration Design to Which Young Engineers Can Relate: The Washing Machine’.
Lt. Col. Wayne Whiteman and Col. Kip Nygren pointed out that ‘virtually every campus has laundry facilities for students. Most students are therefore familiar with the unwanted vibrations that occur when an unbalance of clothes accumulates during the spin cycle.’
Young engineers thrill at bad vibrations. Keying on that, Whiteman and Nygren sketched out, in terms designed to resonate with their audience, the story of how to prevent oscillatory walk. These terms are lyrical, if you are a certain type of engineer, and perhaps someone will use them in a hip-hop hit: Mass of the Entire Machine; Mass of Inner Housing and Rotating Drum; Mass of Unbalanced Clothes; Coefficient of Static Friction with Floor; Radial Distance to Unbalanced Clothes; Spin Speed; Suspension Spring Constant; Suspension Damping Ratio.
Conrad, Daniel C., and Werner O. Soedel (1995). ‘On the Problem of Oscillatory Walk of Automatic Washing Machines.’ Journal of Sound and Vibration 188 (3): 301–14.
Whiteman, Wayne E. and Kip P. Nygren (1999). ‘Basic Vibration Design to Which Young Engineers Can Relate: The Washing Machine.’ Paper presented at the annual meeting of the American Society for Engineering Education, Charlotte, N.C., 20–23 June, session 3268.
The Threat of the Robo-Toaster
Which kind of robot will be the first to arise and smite us? A study called ‘Experimental Security Analysis of a Modern Automobile’ suggests we keep an eye on the family car.
Written by Karl Koscher and a team of ten other researchers at the University of Washington and at the University of California, San Diego, the paper was presented at the 2010 IEEE (Institute of Electrical and Electronics Engineering) Symposium on Security and Privacy, in Berkeley, California.
Unlike the mindless jalopies of the past, the paper points out, ‘Today’s automobile is no mere mechanical device, but contains a myriad of computers.’
This myriad has powers to do good things for us humans, as well as bad things to us. Already, in some cases, the microchip hordes quietly, beneficently take control from the driver. The Lexus LS460 luxury sedan can automatically parallel-park itself. Many General Motors cars will soon have what the study calls ‘integration with Twitter’. Other abilities are just around the corner.
The team’s goal was to look past the goodness, and see how hard it would be to cause trouble.
Limiting themselves to the here and now (‘we concern ourselves solely with the vulnerabilities in today’s commercially available automobiles’), they tell, in professionally dull, let’s-remember-we’re-engineers fashion, how they conducted an experimental reign of terror: ‘We have demonstrated the ability to systematically control a wide array of components including engine, brakes, heating and cooling, lights, instrument panel, radio, locks, and so on. Combining these we have been able to mount attacks that represent potentially significant threats to personal safety. For example, we are able to forcibly and completely disengage the brakes while driving, making it difficult for the driver to stop. Conversely, we are able to forcibly activate the brakes, lurching the driver forward and causing the car to stop suddenly.’
They played other sorts of dangerous tricks, too, with the greatest of ease. At their behest, speeding cars shot windscreen-washing fluid continuously, popped the trunk, blared the horn, and, in a grim sense, had a high old time.
The study focuses on cars. But indirectly, it foresees the day when our very toasters and teapots might turn or be turned against us. On that question there is mystery, if not much dread, in part because there’s little publicly available research about the threat of hijackable household appliances. In 1996, security experts based partly at the RAND Corporation wrote a report called ‘Information Terrorism: Can You Trust Your Toaster?’ Mainly they (1) recommend hiring lots of ‘information warriors’, but warn that (2) law enforcement agencies sometimes squabble, and so (3) ‘information terrorists’ could inflict damage ‘in the time it takes to argue about whose job it is to respond’. More mundanely, Austin Houldsworth of the Royal College of Art in London created what may be the world’s most dangerous teapot, and the quickest. Houldsworth tells how it works: ‘The heating elements within the kettle contain thermite, which ... burns at 2500 degrees.’ (See it in action at http://vimeo.com/5043742.)
Koscher, Karl, Alexei Czeskis, Franziska Roesner, Shwetak Patel, Tadayoshi Kohno, Stephen Checkoway, Damon McCoy, Brian Kantor, Danny Anderson, Hovav Shacham, and Stefan Savage (2010). ‘Experimental Security Analysis of a Modern Automobile.’ Paper presented at the 2010 IEEE Symposium on Security and Privacy, Berkeley, Calif., 16–19 May, http://www.autosec.org/pubs/cars-oakland2010.pdf.
Dress Stress Engineering
Charles Seim is project engineer of the Gibraltar Bridge, the somewhat whimsically proposed megagigantic structure that would join Spain and Morocco, spanning a distance of five miles across the Strait of Gibraltar. He prepared for this perilous task, early in his career, by writing a report entitled ‘Stress Analysis of a Strapless Evening Gown’.
‘Effective as the strapless evening gown is in attracting attention’, Seim wrote in 1956, ‘it presents tremendous engineering problems to the structural engineer. He is faced with the problem of designing a dress which appears as if it will fall at any moment and yet actually stays up with some small factor of safety.’
The study includes two technical drawings. The first is a front view of the torso of a woman wearing a strapless gown. It will be familiar in kind, if not in all its details, to anyone who has studied physics on any level.
Seim’s prose fleshes out the fine points. Here is a typical passage: ‘If a small elemental strip of cloth from a strapless evening gown is isolated as a free body in the area of plane A in Figure 1, it can be seen that the tangential force F1 is balanced by the equal and opposite tangential force F2. The downward vertical force W (weight of the dress) is balanced by the force V acting vertically upward due to the stress in the cloth above plane A. Since the algebraic summation of vertical and horizontal forces is zero and no moments are acting, the elemental strip is at equilibrium.’
Figure 2 offers a detailed side view of the bust. Seim uses it to illustrate the kind of daunting technical challenge that good engineers relish. His prose brings vivacity to the spare draftsmanship and simple mathematical notation. This is how he introduces the chief difficulty posed by the upper surface of the breast: ‘Exposure and correspondingly more attention can be had by moving the dress line from a toward b. Unfortunately, there is a limit stress defined by S = F/2A (A being the area over which the stress acts). Since F/2 is constant, if the area A is decreased, the bearing stress must increase. The limit of exposure is reached when the area between b and c is reduced to a value of “danger point”.’
Over the past fifty years, Charles Seim’s concept of an engineering danger point has inspired many people to see the drama inherent in the analysis of tension, compression, stress, and strain. In 1992, it inspired an homage from jazz harpist and singer Deborah Henson-Conant, a five-movement orchestral composition called Stress Analysis of a Strapless Evening Gown. Henson-
Conant performs this technical gem regularly with symphony orchestras. Each time, she wears a well-engineered strapless evening dress, which she loves. Her hope is to keep it up.
Seim, Charles E. (1956). ‘Stress Analysis of a Strapless Evening Gown.’ The Indicator November.
Pecker Bang Analysis
While others tried to build a better computer or teapot or mousetrap, Julian F. V. Vincent, Mehmet Necip Sahinkaya, and W. O’Shea of the department of mechanical engineering at the University of Bath tried to build a better hammer. Unlike most previous hammer smiths, they studied woodpeckers. Why? Because to mechanical engineers, when they are in a certain frame of mind, a woodpecker is nature’s finest version of a hammer.
The trio published ‘A Woodpecker Hammer’ in a scholarly journal with the unwieldy name Proceedings of the Institution of Mechanical Engineers, Part C, Journal of Mechanical Engineering Science.
There they begin with a nod to the Ig Nobel Prize-winning research of Dr Ivan Schwab of the University of California-Davis School of Medicine, who in 2002 wrote a monograph that explains why woodpeckers don’t get headaches. Schwab was fascinated by the mechanical properties of the woodpecker’s head – especially why its brain doesn’t homogenize during all that pummelling, and why its eyes don’t pop out of their sockets. The Bath scientists take a more holistic approach. They explore how the bird’s entire body, from head to toes, feathers included, effectively function as a simple mechanical tool for pounding wood.
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