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An article by John Tierney in the NY Times “Science Times” reports that many a physics fact can be better remembered if the example given relates to tire drag on the second turn at Daytona.
When Junior Johnson, in 1960, discovered he could keep up with another car by staying close to its rear bumper, he was ready for a new career as an “intuitive physicist.” He suspected, as he put it, that “the air was creating a situation, a slipstream type of thing.”
The term “intuitive physicist is borrowed from Diandra Leslie-Pelecky, who teaches nonintuitive physics at the University of Nebraska. She has written a book, “The Physics of Nascar.”
Dr. Leslie-Pelecky’s interest in Nascar was triggered one evening a couple of years ago. She was taking a break from her research on magnetic nanomaterials, and, channel surfing, she saw a chain reaction of stock cars gone wild.
“It started when six cars were going around the turn, and one of them suddenly started wiggling and went into the wall for no apparent reason,” she recalled. “It was like spontaneous combustion. As a scientist, you look at that and say, ‘There has to be a reason.’ It drove me nuts because I couldn’t explain it. I felt as if I was in a different universe.”
Her curiosity resonated with another project of hers, ways to enliven the science curriculum in elementary and secondary schools. It occurred to her that students would be more interested in, say, the difference between the coefficients of static friction and kinetic friction if the kinetic example involved tires skidding on a turn at Daytona. (You can find her stock-car science quiz at nytimes.com/tierneylab/)
“So many kids lose interest in science because we’ve been teaching them that it’s all about memorizing facts,” she said. “What you do in school that’s called a lab experiment is not really an experiment, because you already know the answer. When you listen to a driver and his crew chief trying to figure out how to give the car more grip in Turn 2, that’s the scientific method in action. They’re asking questions about load transfer and downforce, and they don’t know the answers until they’ve done the experiment.”
Dr. Leslie-Pelecky’ book explains everything from the mechanics of racing engines to the molecular properties of the drivers’ fire-retardant suits. It pays special attention to the endless battle against that great evil force, drag.
Drafting, Junior Johnson — and others – discovered, could help not just the trailing car, but also the leading car; the amount of turbulence at its rear was being reduced.
Two cars drafting together can go 3 to 5 miles an hour faster than a single car. Extra trailing cars add a little more speed, and this is why the drivers spend so much time in single-file bumper-to-bumper traffic.
If the trailing car nudged the leading car, the drivers and their engineers learned, they could add speed. (Crowds loved it.) And that enabled the trailing car, which could go faster than the leading car because it faced less air resistance, to transfer its extra momentum to the leader — a technique called “bump drafting.”
Bump drafting evolved into “slam drafting” as the drivers became bolder and their crews added steel plates to the bumpers.
The math grew more elaborate as engineers combined a classical technique for describing the movement of fluids (Navier-Stokes differential equations) with computers that could calculate the air flow as the car moved under different conditions. Now, racing teams could determine precise ways of reshaping a car to suit each track.
Any car built to minimize drag on Daytona’s long straightaways and sharply banked curves had to be reconfigured for a smaller track, because enough downforce was needed to keep it from spinning out of control on a tight corner.
All this reshaping became so expensive and grueling that Nascar this season ordered everyone, beginning with Daytona, to use the same chassis and body (that Car of Tomorrow) at every track.
Engineers can tinker with just two major aerodynamic features now: a new wing atop the rear of the car, and an adjustable shelf protruding from the front end (called a splitter because it diverts air under or over the car).
But these new limitations haven’t stopped the aerodynamics arms race. Now it is just more refined, as Dr. Leslie-Pelecky kept hearing this past week in the garage at Daytona.
Eric Warren, a fellow PhD who is an aeronautical engineer, is the technical director of Michael Waltrip Racing. To prepare his drivers for the new car, Dr. Warren relied on C.F.D. simulations to calculate the airflow at 100 million points on the vehicle.
“The smaller the gains are to find, the more scientific the approach has to be,” he said. “To pass a car, you need to know precisely where the minimum drag is for you and the maximum drag is for him. With the picture of airflow we get from the C.F.D., we can tell the driver that the ideal passing maneuver is a certain sequence of positions.”
Without revealing that sequence before Sunday’s race, Dr. Warren did elaborate slightly about the how to find “good air” when you are behind or alongside another car.
“Less than a one-foot difference between cars is where a lot of the interactions are,” he said.
Twelve inches or less? Well, that’s the kind of experiment that Nascar fans will be watching for.
Dr. Leslie-Pelecky hopes it will also inspire some future scientists. The old textbook problems involving locomotives lumbering at different velocities out of cities A and B were boring to students– but they might pay attention to two cars traveling 200 miles an hour separated by inches.
sole source: NY Time “Science Times article by John Tierney on 2/12/08. www.nytimes.com “The Physics of Nascar,” by Diandra Leslie-Pelecky, is published by Dutton, at $25.99.
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