Taking a Drive with Sir Isaac Newton

You got a call this morning telling you that you need to pick up Sir Isaac Newton from O’Hare airport.Your task: bring him to the Museum of Science & Industry to show him how far our knowledge of physics and engineering has progressed since he died in 1727. You drive a vehicle that would not have been invented for another 175 years after his death, so there’s no chance he’d understand this confounded contraption, much less be able to take the wheel and get to the museum on his own unscathed.

On the way, you start getting excited to show off what the world has accomplished since his ultimate demise. It’s been almost 300 years since he’s been around, and in that time, scientists have made some major advancements. We must have advanced way beyond Newton’s teachings, right?

Since Newton’s never been in a car before, you are curious how he’ll respond to your automatic horseless carriage with a solid roof and climate control. You pull up to the international terminal (he’s flying in from London), and he comes out dressed in his finest ascot and heels (he hasn’t figured out today’s fashion yet). After a short inspection of the car, he takes a look at the door handle on the passenger door.

Archimedes once said something about using a lever to move the Earth. Pshh…like that would ever work.

The handle is a lever, he surmises — a simple machine first defined by Archimedes in the 3rd century BCE, but probably invented much earlier (as far as we know). Knowing levers balance on a fixed point, like a seesaw does, Newton concludes that the force he applies to the door handle by pulling on it will equal the force that comes out of it on the other side of its hinge, but in the opposite direction. He puts two-and-two together and figures that the handle must disengage a locking mechanism inside the door. He’s a pretty intelligent human being, after all.

Now that he’s in the car, he glances down and notices the two pedals by your feet.

“What are those for?” he asks. You respond,

“The narrow one here is the gas pedal, and the wide one over here is the brake. Gasoline is a form of fuel that makes the car go, and—“

“The brake slows the car down!” he interrupts, proud of his acumen for deductive reasoning. He continues, “I can guess the basic concept of the brake pedal, but how does this ‘gas pedal’ work?”

How an car engine transforms the force of a gas explosion into forward motion.

You describe the basic concepts behind the internal combustion engine, the kind of engine that makes cars go. The car feeds gasoline into the engine, where it evaporates in one of several cylinders. It heats up so much it combusts (or explodes), forcing the pistons in each cylinder downward. The pistons’ movement causes a series of gears, rods, and axles to rotate, causing your wheels to spin and your car to move. It’s just like how your feet pushing on bicycle pedals makes the bike move forward.

“I guess that makes sense. How about this for a bet? I bet you one pound sterling from my very own mint that with the little information you just told me, I can tell you everything else about how the car moves?” Newton said with giddy excitement.

“Oh yeah?” you respond. You’re thinking, this guy’s been dead for 300 years, what does he know? You take the bet.

“I assume cars are just like everything else in the universe in that they follow all three of my laws of motion.”

“I suppose…?

“Take my first and third laws of motion for example: the first goes…let me see if I can remember,” he looks up, squints, and motions with his hand, “an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by a force.”

“That sounds familiar,” you say. Newton continues,

“We’re sitting in the car right now, and it’s not moving; it’s at rest. My first law of motion says that the car will stay at rest unless a force acts on it. To be fair, even though we are not moving right now, there are forces acting on the car right now. But the car isn’t moving because these forces are in perfect equilibrium.”

“What you do you mean, ‘equilibrium?'”

“This is where my third law of motion comes in: every action has an equal and opposite reaction. The car is ‘acting’ on the ground right now – gravity is causing the car to push down against it. But there’s also this thing called ‘normal force.’ This is the force the ground is applying to the car – the ground is pushing up with the same strength as gravity. As a result, the car is not sinking or floating. It’s in equilibrium.”

“You’re such a nerd, Isaac.”

You pull out of the driveway and start accelerating down the street. You speak up. “Is that all you know? That’s not worth your fancy British money!” Newton interjects,

“Oh, I’m not done! Do you know that my laws of motion also explain why the car just sped up just now?”

You retort, “Oh geez…okay, go ahead.”

“No, no, this is interesting, just hear me out!” Newton continues, “remember when I said objects at rest stay at rest unless acted upon by a force? Well, we were acted upon by a force!

“A force causes things to accelerate. In fact, I described how this works in my second law of motion: force equals mass × acceleration. This law implies that the amount of force acting on the car will directly affect how fast it accelerates. It also says that the heavier the car, the more force it will take to make it accelerate. It goes both ways.

“Right now, we’re not speeding up or slowing down, which means the car is in perfect equilibrium again.” You place your hand on your chin and interrupt:

“That means the force of the engine must be counteracting the force pushing it backwards!”

“That’s right! Do you know what that backward force is?”

“Wind resistance?”

“Yes! And also the friction of all the moving parts in the car rubbing against each other.”

It’s actually a lot of things Newton wouldn’t be familiar with:

“You can say friction is keeping us from speeding up, and you can also say the force from the engine is keeping friction from slowing us down. Before, when we were accelerating out of the driveway, the force from the engine was great enough to overpower the force of friction and this caused the car to accelerate.” He pauses and looks ahead. “What’s that red light up there in the distance?”

Proud to realize you know something Newton doesn’t know, you explain traffic lights. You hit the brake.

“Oh, did you feel that?” Newton exclaimed. “That’s my first and second law in action again!

“This time, the force of friction between the brakes and the wheels in your car overpowered the force of the engine, which caused us to slow down. Just like when we were speeding up, the car’s mass affected how much force it took to slow down: the higher the mass, the more force it takes.”

Suddenly, a thought comes to mind, and you have to tell Newton.

“Hey Isaac, you know, they named a unit of measurement after you.”

“They did??” His eyes light up.

“Yeah, it’s called a Newton (duh). It’s a unit of force in the metric system, which is the measurement system of choice in every country except the US and Liberia.

“A Newton is the amount of force that you need to use to accelerate something. To be more specific, when things are accelerating, their velocity is changing: they’re either getting faster, getting slower, or changing directions…and a Newton is the force needed to do that. But as you know, scientist have to standardize everything to make sure that when a scientist in the US says a ‘Newton,’ a scientist in Japan knows exactly how much force that is.

“So scientists decided to define a Newton as the amount of force that make things that weigh one kilogram go faster by one meter per second, every second. Let’s use the car we’re in as an example. One Newton would be the amount of force the engine needs to use to increase our speed from 35 to 36 miles per hour in one second, divided by the weight of the car in kilograms. We took your second law of motion (force = mass x acceleration) and simply added units to it. Force (one Newton) = mass (one kilogram) x acceleration (one meter per second per second).”

“Hey, that’s pretty cool. Wait a minute, you do know about my laws of motion!”

“Okay, fine…I took one physics class in high school.”

“It’s good to hear they’re teaching this stuff in school. Did anyone pick up calculus? You know, I invented that field of study, too.”

“Don’t get cocky, Newton. I also learned that you’re not the only one that claimed calculus as his invention. We think Gottfried Wilhelm Leibniz may have plagiarized you, but mostly, historians today think you and he came up with the same idea independently of each other. How do you explain that?”

Newton turned his head and looked out the window, and neither of you spoke another word for the rest of the car trip.

Newton, the polymath that he was, pops up a lot in Science Unsealed. Read about his role in defining pi, in describing how gravity works before Einstein changed everything, and in explaining how planes stay in the air, hundreds of years before they were invented.