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Professor Diandra Leslie-Pelecky
is a physicist in love with the beauty and power of motorsports and is uniquely qualified to explain how physics translates into winning races.
Dr. Leslie-Pelecky earned her PhD from Michigan State University and joined the University of Nebraska in 1994. Now a professor of physics at the University of Texas at Dallas, her day normally is spent researching magnetic nano materials with potential applications in improving MRI technology and cancer diagnosis. It is a strange and unexpected leap from laboratory to racetracks but her interest in the science of NASCAR was piqued when, while watching a race on television, she witnessed 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”. Replays of the crash showed no obvious causes – no collision, sideswipes, flat tires or engine failures.
As a scientist she knew there had to be an answer. That curiosity, and her need to logically understand what had happened, set Dr. Leslie-Pelecky off on a search of the science behind the sport. Her research took her trackside to pit row, NASCAR R&D crash tests, wind tunnel experiments, “Dyno” engine treadmill tests and more. Along the way she befriended numerous engineers, crew chiefs, mechanics and drivers. She even drove a 600 horsepower car at Texas Motor Speedway to learn more. “Watching a race on TV, you have no idea how different the cars are – they are designed to go left, so if you want to go straight, you have to steer right”.
Based on her extensive access to race shops, pit crews, crew chiefs and mechanics,
Dr. Leslie-Pelecky’s new book “The Physics of Nascar” explains
‘How to Make Steel + Gas + Rubber = Speed”.
Track Chic meets with Dr. Diandra Leslie-Pelecky to learn more about the science and her experience researching the book:
· Did you find your answer – what really did cause that one car to slide and hit the wall?
It was all the result of aerodynamics. The car that slid into the wall had the air taken off its spoiler. (This was in 2006, when NASCAR cars still had spoilers). A car’s grip depends on how well the tires grab the track, and on how hard the tires are being pushed into the track. The air passing over the car helps to push the tires into the track (that’s downforce – the force of the air pushing downward on the car). Whenever two cars get really close to each other, the way air flows around the cars changes. If you don’t get enough air pushing down on the back wheels, you get loose and you end up in the wall.
· You had enviable access to top race teams, mechanics and drivers while gathering
research for your book. What surprised you the most during this experience?
The biggest surprise was how open everyone was. They answered everything I asked, although they would sometimes ask me not to mention, for example, a specific spring rate. The only time I had to get up and leave was when guys were changing clothes in the hauler! A lot of the technical people understand that NASCAR is a great way to get people interested in science because you absolutely cannot win races without having a good understanding of math, science and engineering. They know that it is really important for this country to have a technologically literate workforce and that kids often get turned off science early. Studying motion is much more interesting when it’s your favorite driver going 180 mph.
Tell us more about your experience driving the racecar at Texas Motor Speedway ... your lack of peripheral vision, the g-forces you experienced going through the turns, your intense focus during the drive, and the adrenaline rush of driving 148-150 mph. It sounded like you really enjoyed the experience – even the aftereffects of wobbly legs and a racing heart!
At that point, I’d never even been close to a race car, so I didn’t appreciate how it would feel from the driver’s seat. You have a helmet on, and the helmet pretty much blocks your side vision, plus it makes your head feel heavy. The seat really wraps around you and you’re much lower to the ground than in a normal car (and I drive a pick-up truck, so it felt really, really low). The seat belts keep your torso pretty much immobilized. If you’re claustrophobic, I don’t recommend trying this. There are mirrors in the cars, but I was so focused on holding the line they wanted us to drive that I didn’t look at the mirrors – or the tach – once.
I always say that race car drivers have an intuitive understanding of physics that you don’t get from working problems. I’ve worked the standard problem about cars on banked tracks a zillion times. You know, the one that goes “A car drives 150 mph around a track with a radius of so many feet. How many gs does the driver feel?” You plug in the numbers and you get an answer, like 2 gs. But what does that mean? How many of us get to experience 2gs? After my experience at TMS, I not only have an intellectual appreciation of what 2gs means, I have a gut-level appreciation of it! The next time I do an example for my class, I’ll be able to tell them what 2gs really feels like. The drivers also have a good understanding of impulse, which is how much force you feel when you stop suddenly, but I’m content to leave that one to the professionals.
I was amazed how calm I was during the ride and getting out of the car. I didn’t think we had gone that fast, so I was actually surprised when the instructor told me that I went about 150 mph. It wasn’t until I got out of the car and was standing around, talking to some of the other people, that I realized that my knees felt a little wobbly. I looked down at my hands and they were shaking. Josh Browne, who was Elliott Sadler’s crew chief while I was following the No. 19 car around, told me later that this is adrenaline, and that even professional drivers shake after qualifying. Even if your mind doesn’t know you’re going fast, the rest of your body figures it out pretty quickly.
I got my husband a driving lesson at TMS for a Christmas present, but my next goal is to find a way to get into a car with a pro and experience what drafting feels like.
The funny thing about that is that I am pretty much a scaredy cat. I don’t like heights. I don’t bungee jump or hang glide…I’m not even big on carnival rides, but I loved driving a stock car at TMS. It was so different than I expected – louder, bouncier and it didn’t really seem like we were going that fast. I’m sure that some of it was just because I was so focused. I wanted to capture everything as it was happening, so I wasn’t thinking about how fast we were going.
What question are you asked most frequently?
Everyone wants to know whether people in NASCAR treated me differently because I was female. I think most of the people who ask that haven’t really been around NASCAR because there are a lot of well respected female journalists working in the field, plus an increasing number of women mechanics and engineers, so the drivers and crew members are used to getting good questions from women. It probably doesn’t hurt that physics is a male-dominated field, because – believe it or not – physics culture shares a lot with NASCAR culture. People are focused on their jobs and they pursue the questions they are studying with a hard-driven passion. For me, it’s understanding how to use materials to make chemotherapy less taxing on patients while still treating the cancer. For the folks I followed around the garage, it’s how to get their car going faster. But it’s the same passion. It’s that burning desire to understand something, whether it be people, science or cars. It is great when you get to make your passion your career.
We invited Track Chic members to ask the questions that, like you trying to understand exactly why that car hit the wall, they wanted to fully understand.
1. How does drafting really work, how is it possible that two cars traveling together can drive faster than one car traveling alone? Michelle, NASCAR Super Crew
It’s all about the air. When a car is driving by itself, it has to move the air molecules aside. The air molecules travel up, over the hood and around the sides, then trail off down the rear of the car. If a second car is following some distance back, the second car has to do the same thing (except the air is a lot more turbulent coming off the first car.) However, if the trailing car can get really close to the first car, the air molecules see one really long car instead of two cars. The first car is breaking a trail and the second car takes advantage of that. Also, when the air comes down around the rear of a car, it creates a partial vacuum and that sucks the car backward. If there is a second car trailing very closely, the first car doesn’t experience as much of a backward pull.
This phenomenon is really important at Daytona and Talladega because the cars have limited engine power. The only way to get an advantage is to cut down drag (which is just the force of the air pushing in the opposite direction the cars are trying to move). Drafting decreases drag, which is why two cars can go faster working together than separately.
2. When a driver from behind bumps the driver in front, how is it that both cars aren’t taken out? Sometimes only one car goes into a spin and sometimes neither car loses control. If the same thing happened on the expressway it would result in a major pile-up. Is it skill or science? Linda, Cantrell Pit Crew
Sometimes both cars are taken out. As with much of racing, it is a combination of skill and science. Let’s say you are trailing another car and you bump into it. Your bump, if it is straight on, will make the car in front of you go straight and faster. However, if you bump at just an angle, you’re going to cause the rear of the first car to rotate. If you bump really hard, not even the best driver is going to be able to save the car; however, if you bump a little more gently, a really skillful driver might be able to save the car.
Kyle Busch is phenomenal – I’ve seen him save a car when the car was almost horizontal. Other drivers aren’t as skillful. Ray Evernham said it best in the foreward to the book: Everything in racing is a little bit of science and a little bit of magic.
3. Are there every day applications to drafting techniques I could exercise during my daily commutes to improve fuel efficiency or is speed a necessary component to benefit from drafting? Ashley, Drag Queens
Yes, you can probably save some very tiny amount of gas by getting up close to a semi truck and running in their wake; however, you can do the calculations and show that there is no way you’ll have time to react if the driver in front of you has to slam on the brakes. Saving energy that way isn’t worth the risk of an accident. Some people complain that NASCAR is wasteful because it uses so much gas. The amount of gasoline used in a Cup race weekend is less than the amount of gas used in 2 seconds in the U.S. There are a lot of ways to improve your gas mileage that are more significant–and safer. For example, check your tire pressures every week and make sure your tires are inflated to the manufacturer’s recommendations. It costs energy to deform underinflated tires, and that energy comes from the gasoline. Also, make sure that you keep your car tuned up so that it is burning gasoline as efficiently as possible. Either of these ideas will save you a lot more money than trying to draft a semi on the expressway and they are also a lot safer.
The Physics of NASCAR, How to make Steel+Gas+Rubber = Speed is an excellent guide to help you understand why your driver’s crew chief is increasing tire pressure, adding wedge, lowering the track bar or taking two tires instead of four. But more than that, the book illustrates the immense technical skill, brain power and patience required of race teams today and gives new respect to the science which explains why the sport is so much more than “Go fast, turn left, and don’t crash”.
Thanks to a Woman behind the Wheels, Dr. Leslie-Pelecky has also enlivened interest in science curriculum in elementary and secondary schools. Her involvement in the National Science Foundation-funded program “Project Fulcrum” – which puts graduate students in K-12 classrooms to help teach science – made her realize the more fun and accessible the subject, the more enthusiastic the students will be and the more they will understand. Her new project, ”Building SPEED” (Science Partnerships in Engagement, Education and Diversity), brings the excitement of motorsports into the classroom to motivate kids' interest in math, science and engineering. Today, students are becoming more interested in “the difference between the coefficients of static friction and kinetic friction” based on examples they witness when tires skid in Turn 2 at Daytona. Suddenly it’s more than a lab experiment, it’s a scientific method in action ... full throttle!
To learn more about the Science of NASCAR including everything from
the“Science of Fuel Intake Problems" to
the “Science of Tony Stewart vs. Goodyear”,
visit Diandra Leslie-Pelecky’s website:
www.stockcarscience.com
where you will find Q& A, blogs, calendars of Diandra's radio,
TV, Personal Appearances and more.
Photos: Sarah Pfeiffer Photography, Inc. and Chris Livingston, New York Times
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