Hang tight: Tiny Velcro patch does the trick
DRAWING BY DEBORAH DERR McCLINTOCK
Q. A Velcro manufacturer, as a promotional stunt, offers $1 million to anyone willing to hang from a skyscraper ledge held up only by a patch of Velcro. How large a sticking surface had the hanger better demand? –Christo
A. Amazingly, a five-inch diameter patch of standard Velcro would suffice, even though such a patch could be peeled loose with one hand, says Duke University biologist Steven Vogel in Cat's Paws and Catapults.
BTW, the Velcro hook-and-loop concept comes courtesy of Mother Nature, copied by Swiss engineer and avid walker Georges de Mestral circa 1948 when he studied the design of cockleburs or burdocks that clung to his socks, noting how the tiny burtips snagged the fuzz.
Nylon, then less than 10 years old, proved ideal for manufacturing Velcro's miniature loops, and cut loops became the hooks. Like adhesive tape, the new fastener held strong against a pressure applied over a broad area but peeled easily in response to a linear tearing force.
"Improvements and derivative products have come along, such as stainless steel Velcro (stronger) and silent Velcro (for military use), but the basic material has changed little," Vogel says.
Q. New neighbor out on her driveway tells you she's washing and waxing her Porsche 924 Turbo to get better gas mileage. Isn't this the dumbest thing you ever heard? –B. Boop
A. Better check out her Harvard bumper sticker before saying anything. Maybe she's an engineering student who does a lot of high-speed driving, and just maybe she's laying a little tongue-trap for you.
For there may well be a slight fuel-savings factor at high rates of speed, says Steen Sjolander, mechanical and aerospace engineer at Ottawa's Carleton University. Air drag is at least partly related to surface frictions against the car body. Streamlining helps, as when dust and squashed bugs are scrubbed away and small pits and scratches are wax-filled to reduce air turbulence and enhance efficient flow.
Speeds are critical here: At city speeds of 50 km/hour, the Porsche would lose only 1.3 horsepower to airdrag, but at 200 km/hour 85 horsepower are lost. Actually, surface finish accounts for only a little of this loss, with most stemming from the large turbulent wake behind the car, plus smaller wakes behind protrusions such as side mirrors.
"So the car washer who drives at German autobahn speeds might notice a small fuel consumption effect, but probably less than comes from keeping tires properly inflated," according to Sjolander.
Q. Who has been billed as "The Man With the World's Strongest Teeth"? –L. B. Dickens
A. On April 4, 1974, John Massis of Belgium clamped his teeth down on a special bit attached to a long thick rope tied to two New York Long Island railroad passenger cars totaling 80 tons. Then he leaned his body back for the tug of his life.
Without using his hands, but pushing off with his feet against railroad ties, the muscular 180-pounder applied a rope force at a 30-degrees-incline that actually moved the cars several feet, recount David Halliday et al. in Fundamentals of Physics.
Astonished photographers recorded the event, and from the look of the setup, Massis probably had to muster several hundred pounds of neck-and-jaw exertion for the railroad roll. Not recommended by your local dental association.
Q. Do skyscrapers come equipped with "shock absorbers" to cope with wind shimmy near the top? –D. Trump
A. Most don't. But a 95-mph hurricane howler can
exert forces of 30 pounds/square foot, says Penn State architectural engineer M. Kevin Parfitt. Multiplied out over a mere 100-ft.-by-100-ft. section yields 150 tons! This can set a tall building rocking back and forth as much as a couple of feet at the peak.
Some skyscraper wind shimmy is inevitable, but it can cause scary creaks and groans, water sloshing in sinks and toilets, and "sea sickness" for occupants, reports "NYC24."
One counterstrategy, says Parfitt, is the "tuned-mass damper."
At New York's 915-ft. Citicorp building, in a room at the top, a 400-ton block of concrete slides on oil, between springs and a hydraulic piston. When the building sways one way, the concrete goes the other, stabilizing.
Even so, Citicorp does one complete sway every seven seconds. Just hope that on a very windy day, the tall- building bunch holds onto lunch.
Send Strange questions to brothers Bill and Rich at
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