# How an Engine Works (Super-simplified with a Tricycle, a Sink, and Exploding Cars)

This post was adapted from a section I had to cut from an early draft of a book.

Today I’m going to explain how a gasoline engine works, using things you already understand: a tricycle wheel, a spray bottle, a syringe, and a bathroom sink.

Remember when you were little and you had a tricycle?

After you’d pedaled up and down the block a hundred times, you probably experimented with things like pedaling with just one foot. You discovered that if you pushed down hard enough, the momentum of the bike kept the wheel going and brought the pedal back up again.

Remember shuffling your shoes on the carpet and then touching your sister on the ear? (Don’t try to deny it, I know you did this.) Of course, zapping your sister would hurt you too, unless you figured out that you could hold something metal in your hand, and that would conduct the electricity.

Another fun toy was the syringe.

You could fill the bathroom sink full of water, stick the syringe in, pull the plunger back and it would suck up water. Then you could press the plunger forward and shoot water at your sister.

And there was always the squirt bottle. Useful for squirting sisters or just misting yourself when it was hot.

What do these things have to do with a gasoline engine? Believe it or not, you already understand all the basic parts of an engine. Here’s a really simplified engine diagram.

Let’s start with the piston. This is a lot like the plunger in the syringe. It slides up and down inside a cylinder. When you pull the piston down, it sucks in air. When you push the piston up, it pushes the air out. The crank is like the pedal on your old tricycle and the connecting rod is like your leg. When you turn the wheel, the crank pushes the cylinder up and down. The valves you see at the top of the cylinder work just like the drain plug in your bathroom sink. They open and close to let air in or out of the cylinder.

Now let’s look at the fuel. You’d think from Hollywood movies that a tank of gasoline is a bomb, just waiting to go off. After all, any time a car goes off a cliff in a movie, as soon as it hits the bottom, it explodes in a big fireball.

Sadly, cars rarely explode in real life. Gasoline is flammable, but in order for it to explode, it needs to be mixed with air first. That’s the job of the carburetor (or in some engines, the fuel injector). It’s a lot like the spray bottle. It sprays fuel in small droplets so the fuel mixes with air. Once gasoline is mixed with air, it’s very dangerous; even a small spark will set it off.

That brings us to the spark plug. It’s really just an insulated piece of metal that sticks down into the cylinder.

Now let’s start things going and watch what happens. When you turn the ignition on a car, an electric starter motor turns the crank, which moves the piston.

First, the intake valve opens, and the cylinder starts down. This sucks in air, and the carburetor sprays fuel into the incoming air.

When the piston gets to the bottom, the intake valve closes, and the piston starts back up. This squishes the air and fuel together, which makes it even more explosive.

When the piston gets to the top, a high voltage charge is sent to the spark plug, which makes a spark inside the cylinder.

The fuel/air mixture explodes, and the explosion forces the piston down.

As the piston is forced down, it turns the crank. This is like stepping hard on the pedal of the tricycle wheel. The momentum from this stroke will keep the crank turning, so we don’t need the starter motor any more.

When the piston gets to the bottom, the exhaust valve opens. Then the piston starts back up, pushing the exhaust gasses (the smoke) out of the cylinder, and out the exhaust pipe.

When the piston gets to the top of the cylinder, the exhaust valve closes, the intake valve opens, and the cycle starts all over again.

Real engines are a bit more complicated than this super-simplified example, but all gasoline engines work on these basic principles.

Now go apologize to your sister.

# How the GPS System Works (Super-simplified with Battleship and The Da Vinci Code)

This post is adapted from a section I had to cut from an early draft of a book.

## Super-simplified explanation of the GPS system

I’m going to explain how the Global Positioning System works. But first we’re going to play a game and then read The Da Vinci Code.

## A quick game

This game is called “Og Hunt.” It’s a bit like the classic game, Battleship, but in this case you don’t just find out if you hit or missed the target, I’ll also tell you how far away you were.

We’ll play this game on graph paper, starting with a grid.

The Og is hidden somewhere in this grid, but you don’t know where. So you take a random guess, and say “B2.”

I tell you, “You missed. You were five squares away from the Og.”

Now you could just keep trying coordinates randomly, until you hit the Og, but this could take a lot of guesses. But you’re smarter than the average bear. So you pull out the compass you carry with you for just such an occasion, and you draw a circle with a radius of five, with the center at the point B2.

Since B2 was 5 squares away from the Og, you know your target must lie somewhere on that circle. Now you make a second guess. “B7.”

I tell you, “You missed. You are 3.16 squares away from the Og.”

You know you’re getting closer, but more importantly, you can draw another circle.

You know the Og must be somewhere along that circle you’ve just drawn, and it also must be on the first circle. The circles cross in two places, so the Og must be at one of those two intersections. Aha! One of the intersections lies outside the grid, so you know the Og must be at the other intersection, at E7.

“Hit! You found the Og!”

Well, that was fun! Now let’s get on with learning how the Global Positioning System works.

## Lots of satellites

The first part of the GPS system is 32 satellites, circling the earth in all sorts of different orbits so that there are always at least 3 of them overhead, no matter where on the globe you are. Each satellite is constantly transmitting a radio message with two things in it: exactly where in space the satellite is at that moment, and the precise time it sent the message.

The second part of the GPS system is the receiver. There are dedicated GPS receivers, but you can also find them in car navigation systems and in most smart phones. You may have one in your pocket right now.

Before we go on, let’s take a break and talk about how the GPS system doesn’t work, since there’s an awful lot of confusion about that. A good example of getting it wrong is in The Da Vinci Code:

“Look in your jacket’s left pocket,” Sophie said. “You’ll find proof they are watching you.”
Langdon felt his apprehension rising. Look in my pocket? It sounded like some kind of cheap magic trick.
“Just look.”
Bewildered, Langdon reached his hand into his tweed jacket’s left pocket – one he never used. Feeling around inside, he found nothing. What the devil did you expect? He began wondering if Sophie might just be insane after all. Then his fingers brushed something unexpected. Small and hard. Pinching the tiny object between his fingers, Langdon pulled it out and stared in astonishment. It was a metallic, button-shaped disk, about the size of a watch battery. He had never seen it before. “What the… ?”
“GPS tracking dot,” Sophie said. “Continuously transmits its location to a Global Positioning System satellite that DCPJ can monitor. We use them to monitor people’s locations. It’s accurate within two feet anywhere on the globe. They have you on an electronic leash. The agent who picked you up at the hotel slipped it inside your pocket before you left your room.”

A “GPS tracking dot” does not really exist, but the most important error in this scene is there’s a GPS receiver transmitting its location to a GPS satellite. In reality, it’s the other way around. The GPS satellites transmit their location to your GPS receiver. The GPS satellites don’t know where you are. A lot of movies and books make this mistake, so we won’t rip on Dan Brown much here.