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The Isaac Newton School of Driving Physics and Your Car
By Barry Parker The Johns Hopkins University Press Copyright © 2003 The Johns Hopkins University Press
All right reserved.
ISBN: 978-0-8018-7417-8
Chapter One Introduction
New cars, with their sleek, shiny, curved lines, are objects of intrigue, elegance, grace, and beauty. They are exciting, and they can be a lot of fun. The thrill of the first drive in your new car is something you remember for a long time. The science of physics also has a certain beauty and elegance. With a few simple principles and the enormous power of mathematics, you can make amazingly accurate predictions about everything from atomic interactions to the expansion of the universe. And you can also make important predictions about cars.
In this book I bring cars and physics together. At first you might not think they have a lot in common, but they do. It's easy to show that every branch of physics is represented somewhere within an automobile. Mechanics, the branch of physics that deals with motion, is particularly applicable. After all, cars move, and if they are moving they have a certain velocity, and to set them in motion you have to accelerate them. Furthermore, to accelerate them you have to apply a force, and this force comes from a source of energy. Physics is at the basis of all of this. Indeed, two of the main terms that are used in relation to cars arehorsepower and torque, both of which are important terms in mechanics.
Another important branch of physics deals with elasticity and vibrational motion, and these concepts are significant in relation to a car's suspension system. Heat and thermodynamics are critical in engine performance, while electricity and magnetism are what allow you to start the engine and keep it running. With modern additions such as telematics (see chapter 11), wireless communication-which takes place by means of electromagnetic waves-is becoming increasingly significant in cars. It's easy to see that physics is critical to the understanding of cars; it also has helped improve them and has made them much safer.
I taught physics at the university level for 30 years and I grew up around cars, so it's perhaps natural that the two eventually came together for me. My father was a mechanic and a garage owner. As a teenager, I worked in everything from the parts department to the collision repair and lubrication departments. I don't think anyone would have trusted me to do a full-scale repair on an engine at that time, but that didn't stop me from taking apart the motor in my own car. For a while I thought of becoming a mechanical engineer and designing cars. It was something that particularly appealed to me, but after looking into it I realized there were not a lot of jobs in the area so I ended up going into physics. After I graduated and began teaching I soon realized that my students had a lot of interest in cars. Whenever I used examples from the "automotive world" to illustrate a principle of physics, their interest seemed to pique. So I continued the practice as much as possible.
One of the things I enjoyed when I worked at the garage was driving the new cars. A car that stands out in my memory is a yellow convertible. We didn't see many convertibles at that time, so this one was a novelty. After referring to it as "yellow" several times, I was politely informed that it wasn't yellow-it was "sportsman's green." It didn't look green to me, however, and I continued to think of it as yellow. In any case, much to my delight, I managed to drive it around town a few times. What made me think about the car now was a recent issue of Automobile magazine, which featured the Lamborghini Murciélago on its cover. Now, that's what I call "sportman's green." You've heard of shocking pink; well, this one is "shocking green." The article about the car is appropriately titled "Bat Out of Hell." Upon reading it I learned that the Lamborghini gets its name from a Spanish fighting bull. Apparently the first Murciélago's life was spared in the bullring by a famous matador in 1879, who admired its fighting spirit and courage. Instead of killing it, he named a car for it (though that happened much later).
The Lamborghini is a beautiful car (fig. 1). In fact, everything is beautiful about it except the price, which at $273,000 is out of my range. Since I'm writing a book on cars you might wonder what I drive. As an avid fisherman, hiker, and skier, I've owned mostly SUVs over the past few years. They seem to fit in best with my lifestyle.
Unlike most science books, this book does not get more complex as you get into it; in fact, chapter 2 might be the most complicated part of it, since it contains more mathematics than most of the later chapters. I've tried to limit the math, but a certain amount is needed for a good understanding of the physics. In some cases I've omitted the derivation of a formula, but this shouldn't affect the understanding.
Chapter 2 deals with the basic physics of driving. It's concerned with speed, velocity, acceleration, and the forces you experience when you're in a car. The level of the physics is approximately that of a high school physics class, and concepts such as momentum, energy, inertia, centripetal force, and torque are explained. All of these aspects are important in relation to the motion of a car.
Chapter 3 is a key chapter. It's about engines and how they work, and that, of course, is what cars are all about. You wouldn't get very far without an engine. I start out with a little history, which is interesting to most people, but the central topic is the four-stroke combustion engine and how it works. Efficiency is a critical part of any engine and I define several different efficiencies: mechanical efficiency, combustion efficiency, thermal efficiency, and volumetric efficiency. Everyone is interested in comparing not only the efficiency but the horsepower, torque, and other elements of modern cars, so I include several tables for that purpose. I also discuss turbochargers and superchargers briefly, and the role of heat in the engine. The chapter ends with a discussion of diesel engines and the rotary engine.
Chapter 4 is about the electrical system of the car, and I've had many interesting experiences with electrical systems. One of the earliest occurred many years ago, before I knew much about them. My wife and I were coming home from a short vacation. It was dark and the rain was pouring down so hard that the wipers could hardly keep up with it. All of a sudden the engine stopped. I wasn't sure what to do; I didn't even have a flashlight in the car, but I knew I had to check under the hood. After all, something was wrong, and it was possible it could be fixed. So out I went and popped up the hood. The only light I had was from passing cars but I quickly checked everything I could. There were no loose wires, and I checked the points, condenser, and rotor. As far as I could see, everything was okay, but by the time I was finished I was soaked through to the skin. I put the hood down and got back in the car.
"Did you get it fixed?" my wife asked.
I shrugged as I tried the starter, and as I expected it didn't start. To make a long story short, I sat for another fifteen minutes, not sure what to do, when to my relief it suddenly started. I found out later it was a problem with the electrical system. I decided then and there that I better learn more about this system.
So in chapter 4, I cover the basics of electricity and circuits, but I also talk about the starter and the basic physics behind it, and the alternator or generator and how they are regulated. Finally, I discuss the ignition system and the interesting physics behind it.
Chapter 5 is about brakes, and brakes are all about friction, which is an important element throughout physics. Brakes are one of the most important parts of a car in the sense that if they aren't working properly, or the braking conditions are poor, you're in trouble. When I worked in the garage, one of my jobs was to jockey cars back and forth between some of the nearby towns. One morning I was told to take an old half-ton pickup to the next town, so I looked it over as I got ready to go. The hood didn't seem to be snapped down properly so I banged on it a couple of times, but that didn't help much; nevertheless, I didn't worry about it. The road to the next town was along a lake, and I knew the dropoff in the lake was steep-the water was black only a few feet from the edge, and there was no sign of the bottom. I had never given the dropoff much thought before, however.
As I got the truck up to about 60 mph I noticed that the hood was starting to vibrate. Soon it was banging. I didn't like the sound of it, but since I had checked it before I left I was sure nothing would happen.
Suddenly something crashed into the windshield. It made such an enormous noise that I'm sure I jumped a few inches off the seat. I was so startled that it took me a moment to realize what had happened: the hood had flown up across the windshield. I couldn't see a thing. All I could think about was the dropoff that was only a few feet away from the edge of the road.
I tried to roll down the window as quickly as possible, but it only rolled partway. By now I had jammed on the brakes, but I was still doing 40 or 50. If I didn't get it stopped fast I knew where I would end up. I opened the door and peered out and was surprised to see that I was still on the road-I had expected to hit the water any second. Somehow, I finally managed to come to a stop. There wasn't much that was good about the old truck, but-thank heavens-it had good brakes. And that experience gave me an appreciation of brakes.
In chapter 5 we will also look at the different types of friction, stopping distances, tire traction, hydraulics and the brake system, and ABS, the antilock braking system.
From brakes we turn to the suspension system and transmission in chapter 6. Although they aren't related to each other, I cover both in the same chapter. Both have a lot of physics associated with them. In Giancarlo Genta's comprehensive book Motor Vehicle Dynamics the chapter on suspension systems is one of the longest and most complicated in the book. He deals with every possible aspect of suspension systems in considerable mathematical detail, and unless you have a degree in engineering it's unlikely you could understand it. It's not my intent to get into that much detail, but I would like to give you some feeling for the basics of suspension systems, and the physics behind them.
The transmission system is, in many ways, the most complicated system in the car. It is the major component of the power train to the back wheels. The power train has the task of conveying the rotary motion developed in the engine to the back wheels, and overall there are a lot of things that have to be taken into consideration. The basic component of the transmission system is the circular, toothed gear, which itself is quite simple. The complication comes when you start bringing gears together. In this chapter we will look at how gears work and why planetary gears and compound planetary gears are needed in a car.
In chapter 7 we look at the aerodynamics of cars. I've always had an interest in aerodynamics. I suppose it goes back to my interest in airplanes when I was young: model building was my passion, and I spent much of my time building and flying model airplanes. Central to this chapter is the coefficient of aerodynamic drag, which tells us virtually everything there is to know about the aerodynamics of cars. As we will see, this coefficient has slowly been coming down over the years. In other words, cars have become more aerodynamic, and not only does this give the car more eye appeal, but it saves a lot of gas. In this chapter, we will also look at drag forces of all types, streamlines and airflow around a car, Bernoulli's theorem, and aerodynamic lift and down-force and how they affect the stability of the car.
Chapter 8 is a brief course on car collisions. Physics is, after all, the science of objects that interact with each other: atoms smashing into one another, molecules of a gas colliding with one another, and balls and other objects of various kinds bouncing off one another. It's pretty obvious that this concept can be extended to the collisions of cars. I'm not sure it will help you avoid a collision, but it will give you an appreciation of the tremendous forces involved in a crash, which may give you an additional incentive to avoid one. So, in this chapter we will discuss head-on collisions, glancing collisions, the reconstruction of accidents to determine how fast the cars were going, and crash tests.
In chapter 9 we turn to the physics of auto racing. Auto racing is, indeed, a popular sport, and it has a lot of fans. I just finished watching the biography of Enzo Ferrari on TV, and I was intrigued. It was the fascinating story of someone who overcame many difficulties and ended up a legend in the annals of car racing. In 1916, while still a teenager, he lost both his father and his brother, then two years later he almost died of influenza. With the end of World War I, he was penniless and couldn't find a job. Still, something happened at this time that changed his life. He tried to get a job at Fiat, the largest car manufacturer in Italy, and was turned down. At the time, Fiat had the best racing cars in the world, and Ferrari vowed he would build race cars that were even better than Fiat's-and indeed he did. What I found particularly interesting was that Ferrari, who is now renowned for the Ferrari luxury cars, had almost no interest in any of the cars he manufactured except the racing cars. Racing was his passion, and he made luxury cars only to get money for his racing cars. His drivers won over five thousand races during his lifetime, a record for any one person. Nevertheless, he will no doubt be most remembered for his luxury cars.
There's a lot of physics in car racing. Tires, the shifting of weight as the car moves, the position of the center of gravity of the car, the moment of inertia of the car-all are important, and all are determined by physics. Racing strategy, which is critical to the racing driver, also depends on the principles of physics.
Chapter 10 is a little different from the preceding chapters. It's on traffic, or more specifically, on traffic congestion. Everyone has encountered traffic congestion at one time or another, and I always breathe a little easier when I finally get through a large city's traffic jams. Luckily, I don't have to battle large amounts of traffic every day as some people do, and I feel for them. I looked forward to writing this chapter because it involved one of my favorite topics: chaos. I had, in fact, just written a book on chaos, so that was helpful.
Some of my books were displayed at a recent book fair. One of them was the book on chaos. Someone picked it up and looked carefully at the colorful picture on the cover.
"H'm ... chaos," he said. "Sounds interesting. What is it?"
I was sure the technical definition ("sensitive dependence on initial conditions") wouldn't appeal to him, so I explained that an example of chaos is the path of a leaf floating on a turbulent stream that was filled with rapids.
"Oh," he said, with a puzzled look on his face. "Why would anyone want to study that?"
Even though I didn't say it, I wanted to tell him that chaos was revolutionizing all of the sciences and thereby changing the world.
Chaos is, indeed, an intriguing branch of physics (if I may call it that), and it is growing in importance. One of its major applications in recent years has been to study traffic congestion, with some important results. Another closely allied area, referred to as complexity, is also giving insights into traffic control. Complexity is concerned with complex phenomena that are not quite chaotic.
Chapter 11 is about cars of the future and some of the devices they are likely to contain. Whenever I think of cars of the future I'm reminded of the TV show Knight Rider, which ran from 1984 to 1986. It starred David Hasselhoff and his talking car KITT. KITT was a futuristic TransAm with a quirky personality which had turbo boosters and helped to solve crimes. Of course, with such a hero car, there also had to be a villain car, and it was called KATT. The show made Hasselhoff and KITT household names for several years, and fan clubs still exist. In this chapter we look at electric hybrids, fuel cells, flywheels, and ultracapacitors, along with telematics and all the innovations it is likely to bring.
(Continues...)
Excerpted from The Isaac Newton School of Driving by Barry Parker Copyright © 2003 by The Johns Hopkins University Press . Excerpted by permission.
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