### An Inside Look at the Physics of NASCAR

Welcome to The Physics of Cars week here on PhysicsBuzz and what better way to kick off the week than with an interview with Diandra Leslie-Pelecky, author of the Physics of NASCAR!

What are some of the biggest ways that Physics and NASCAR intersect?

How don’t they? I think probably one of the most interesting things is that I asked someone one time if they had people in physics working there because most of the people at NASCAR are engineers. And the person thought for a moment and said ‘No I don’t think we do because you guys think everything interesting is obvious.’ And If you think about it what racing is mostly about is friction and air resistance which is the two things that we tend to like to just ignore. Everything about making a car go fast on the track has to do with the friction between the tires and the track, and so you have to get into some fascinating things like the friction of rubber, which is different than anything we teach our students about because it’s a different type of friction than the kind of friction that you have when you have a wood block moving over sandpaper.

Do you think that NASCAR looks at science from a different angle, in that it focuses more on the practical applications of it?

In real life you can’t make all the approximations we like to make to have a nice neat system in physics. We do the car going around the corner, and we’ll have a coefficient of friction, but we won’t talk about things like the coefficient of friction will be slightly different because the weight of the car shifts as it goes around corners, and so each tire actually has a different amount of grip. When we work physics problems, we try to make them as simple as we can and so we neglect things. As it turns out in everyday driving, that’s not such a big deal. But when you start pushing a car to its limit, you just can’t ignore all those things. They become very important.

How are physicists working on some of the NASCARs that we see?

I think that one of the most important things that physicists bring to motor sports in general is the ability to look for overall patterns and to try to model things. That is, ‘What can I actually ignore here?’ I think the engineers are trained more for ‘Here’s an equation, plug in numbers and go for it.’ The people who have a really strong physics backgrounds are the ones that come up with some of the most interesting innovations.

Like what kind of innovations?

For example, there’s a young man named Tommy Wheeler who has a physics degree from Davidson. and he is an engine person. When you talk to him you just hear him thinking about things very differently, its not tied to the ‘well this rule says this’ it’s ‘I understand the very basics of this so lets come up with something different, come up with a new kind of coating for the engine, come up with a way for reducing friction that way,’ for example.

What would you say is the most interesting thing you’ve learned while researching the physics of NASCAR?

I would have to say aerodynamics. That’s the other component right, air resistance. These cars get a huge amount of grip from the air rushing over them because the force going over the car is an aerodynamic force, so it goes like V squared, speed squared. So, what’s important to us at 60 miles an hour is nine times more important when you’re going 180 miles an hour. When you think about the amount of force that is pushing the tire into the track, it’s basically the weight of the car. Well now I’m going to go 180 miles an hour and I’m going to get a couple of additional thousand pounds of force pushing on those tires. So you’re getting force that’s essentially equivalent to what the car weighs in addition, but only when you’re going fast. It’s sort of a really interesting thought because when I slow down to go into a corner, I lose grip, just because I slowed down.

What’s new in NASCAR recently that you find exciting?

The thing about NASCAR is that they try to keep things very equal. They’ve taken a lot of the ability to explore out of the game. If you want to talk about somewhere where there are some really interesting things going on, there’s a racing series called the American LeMans Series. They are actually working with the Department Of Energy and the Environmental Protection Agency and they allow the teams to use alternative fuels. So there are some folks using diesel, there’s some folks using regular old gasoline, there’s E-85 and my favorite is they introduced a brand new isobutanol based fuel. The neat thing about isobutanol is that unlike ethanol, it doesn’t have the same negative effects on seals and things. So it’s got really good energy density, and we could probably use the same infrastructure now for gasoline, which we really can’t use for ethanol. They introduced that in, I think it was 2009 they were using it on the track, and you’re just now starting to read about it in the mainstream press. It’s actually a blend; it’s British petroleum, its called IBE-20, so it’s part isobutanol, part ethanol and part regular gasoline.

Last year NASCAR started using bio-fuels, what kind of effect has that had?

They’re using an E-15 fuel, so it’s really not all that different from what you or I would use in our cars. What it’s done mostly is that it’s really confused the crews about fuel mileage. There’s been a lot of people running out of fuel. There’s been a whole bunch of races where people were all set to win and they just ran out of fuel on the last lap because they’re cutting everything as close as they possibly can. So one of the things about ethanol is that its highly hydroscopic, it sucks up water like crazy. That’s a real problem with the fuel. The problem is that you’re going to put in a certain amount of fuel, and they weigh the fuel so they weigh the can, they put the fuel in and they weigh the can and figure out about how much fuel they got in there. If some of that mass is water and not fuel, water doesn’t combust very well.

That can’t be very good for the engines.

It’s not very good for the engines. The small amounts that they’re getting in there probably aren’t harming the engines, but they’re definitely changing the power. Another thing they’ve found is that the engines run slightly hotter, and the energy density of ethanol is less than that of gasoline, so the more ethanol you put in, the worse mileage you’re going to get. I think they thought ‘Well we should be able to figure out what the mileage is pretty easily,’ before they used to be able to calculate it, but there’s a bunch of people who have been fooled a couple of times now.

Do you think that they’ll be able to get their predictions right for the next couple of seasons?

It’s like everything else, the more experience they have with it, the more records they have. The problem is that when you change something, you basically wipe out all your previous data. So they’ve made a number of aerodynamic changes for example. When they make an aerodynamic change, you take everything that you know from a particular track and a particular car, and you throw it out the window and you start over.

What kind of aerodynamic changes?

They used to actually have an air dam on the front of the car, which was just a piece of plastic that went straight down. The idea was it would go down and seal off the front of the car to the track, so that air wouldn’t get underneath the car. Air underneath the car is never a good thing. They changed that to something called a splitter, and a splitter is sort of like an L-shaped shelf that comes out. When the air comes in, it comes on that shelf, it goes around the car and it pushes down, and so you get additional down force, additional aerodynamic down force pushing down on the car as a result of having that splitter there. That changed a lot in terms of the teams and how they can set up the car and how it responded to different things.

What’s some new and exciting technology in the automotive world in general?

There’s a lot of it if you look at everything being done with electric vehicles. They’re actually about to start, and I believe this is starting in England, there’s going to be a racing series that’s going to race electric vehicles that go 200 mile per hour.

Is it like Tesla Roadsters and things like that?

Yah. I mean they’re not Teslas, they’re all pretty much originally designed. There’s a gentleman in England named Lord Drayson, and he ran a robotics and pharmaceuticals company, he has a PhD, and he also like racing cars. So he was the minister for science and innovation in the British government until the last turnover in power. But he’s been a huge proponent of using motorsports as a way to sort of advance what we know and the cutting edge of cars. Not to mention getting people interested in these technologies, because if you show me a Prius, my response is sort of like ‘eh,” that’s nice, but Porsche just introduced a hybrid that goes 180 miles an hour, and it’s a really nice looking car. That’s going to get me a lot more excited than a Prius.

Do you see a lot of NASCAR technology crossing over into the consumer auto market?

There’s not so much from NASCAR. I’ll tell you where there is crossover is in safety. When auto companies are doing there testing for safety, they’re looking at speeds of 60, 70, 80 miles an hour. They don’t do extensive testing at very high speeds. The NASCAR cars are instrumented, they have a lot of accelerometers on them and so when there’s a crash, it’s very valuable data. They can use that to understand at the limits of speed, what’s actually happening to a car. My former institution the University of Nebraska, the Midwest roadside safety facility is responsible for the barriers that are around the track. They call them ‘soft walls,’ they’re not soft, but they’re softer; they have a bit of give to them. That group has worked with a number of other groups and NASCAR to really push what we know about how the human body and how cars respond to the extremes. I think the safety aspect is what has benefitted the public the most from NASCAR as opposed to the cars themselves.

How does knowing the science of NASCAR affect how you watch a race on TV?

One of my favorite things is to watch a car that starts off really bad and gets better. You track his lap times, and you can listen in on what the crew chief and the driver are saying to each other, and it very much reminds me of trying to debug an experiment. The graduate students in a lab say ‘well I did this, this, this and it’s doing this,’ and you say ‘well ok lets try changing X, Y and Z’ and you change those and they go and they try it and they come back and they say ‘well this is fixed but that’s not.’ It’s the exact same thing on a car. The driver will go in and say ‘when I go into the corner I’m fine, but when I’m coming out I can’t get on the gas because the rear end wants to slide out from under me.’ So the crew chief has to look at the entire car, and go ‘OK, what can we try and change to make that better?’ So when they come in for a pit stop they make a change and then they’ll go and pull out and the driver will say ‘hey that’s better’ or ‘no you didn’t fix it and you made this worse.’ And then it’s time dependent, so for example as the temperature of the track changes, the amount of friction changes. They get less friction as the track starts heating up; as the tires wear they get less friction, so the friction that you get on lap one with a set of tires is going to be different than you have on lap 30 with a set of tires. So it’s all these things constantly changing that crew chiefs are trying to keep up with and they don’t have direct data, all they have is what the driver is telling them. The driver is sort of the data acquisition system for this. So for me it’s a lot of fun watching that process, watching them trying to debug the car in real time. And then the other thing is I know people, and so I’ll be watching and I’ll be cheering for my friends.

Are you cheering for the driver or the crew?

I guess it’s a little of both. People don’t think of racing as a team sport, but it very much is. There’s the people that build the cars, the people that come to the track and get them ready, the mechanics, every team has an engineer or two they spend most of the weekend running simulations trying to figure out if you change this spring what happens to our ability to go fast.

What first got you interested in writing about the physics of NASCAR?

It was a total fluke because I was never interested in racing. I was watching television one day, I was just flipping through channels and I happened to see a race and normally I would have flipped right past it. But before I could do that this group of cars came around a corner and of then just sort of spontaneously went into the wall. I looked at that and was just kind of like ‘what?’ It made no sense, why would this one car out of the group all of the sudden go into the wall? They kept replaying the accident, because it took a while to clean up, and I’m watching and I’m going ‘nobody hit him, there’s no flat tires, his engine didn’t go bad, he wasn’t going any faster than anyone else, what happened?’ And that got me very interested, and the more I looked for answers the more I found other questions and I started realizing that this is all the same stuff we want our students to learn. It’s a lot more interesting when you’re looking at it on a racecar than a block sliding down an inclined plane. I think that’s one of the big challenges we have with physics; when we teach it I don’t think we show people where it enters their lives every day. When you go around the corner fast and you hear the tires squeal, that’s physics. Why do you have to slow down after exiting a highway off a cloverleaf, and why if you don’t slow down do you feel like you’re moving outward? Well, that’s the lack of centripetal force. This is all physics, and I think that people think of physics as people in lab coats do in big facilities in Switzerland. And yah, that’s true, but it’s also something that every one of us does every day.

Photo of Diandra Leslie-Pelecky by Sarah Pfeiffer

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