Cars · Lesson 1 of 15Beginner7 min read

The Big Picture

A car is a team of systems with one job: turn stored energy into motion you can steer and stop. This lesson gives you the map. Every later lesson zooms in on one part of it.

From stored energy to a moving car

A gasoline car carries its energy as fuel. A pump sends fuel from the tank to the engine, where it’s mixed with air and burned. The hot gases push pistons, the pistons turn a crankshaft, and the transmission carries that turning motion to the wheels. A diesel works the same way, except the fuel lights from the heat of squeezed air instead of a spark.

An electric car carries its energy in a large traction battery. Power electronics feed the battery’s electricity to a motor, and the motor turns the wheels through a transmission. There’s no fuel tank, fuel pump or tailpipe. A hybrid uses both an engine and one or more electric motors.

Whatever the energy source, the last step is the same: the tires push backward on the road, and the road pushes the car forward. That’s Newton’s third law at work, and it’s why the small patches of rubber touching the ground matter so much.

The same job, two ways. Both end at the tires, the only parts that push on the road. Sources: U.S. Department of Energy, Alternative Fuels Data Center.

A map of the systems

Here are the systems drawn inside one car. Point at a system (or tap its name below) to see what it does, and click it to open its lesson. Switch to the electric car to see what changes.

The car is drawn as a front-engine, rear-wheel-drive sedan so every part shows. Most front-drive cars combine the transmission and differential in one unit called a transaxle.

The systems at a glance
Part	What it does	Signs of trouble
Engine	Burns fuel and air to turn the crankshaft.	Knocking, loss of power, oil use, a check engine light.
Air, fuel and spark	Measures air, adds the right amount of fuel, and lights it at the right moment.	Hard starting, rough running, poor fuel economy.
Cooling and lubrication	Carries extra heat away and keeps metal parts on a film of oil.	Temperature gauge climbing, coolant or oil leaks, the oil light.
Exhaust and emissions	Carries burned gases out and cleans them up on the way.	Loud rumbling, a rotten-egg smell, the check engine light.
Electrical	Starts the engine, runs lights and computers, and recharges the battery.	Clicking when you try to start, dim lights, the battery light.
Transmission and drivetrain	Matches engine speed to road speed and splits power between the wheels.	Slipping, harsh shifts, clunks, red fluid drips.
Brakes	Turn the car’s motion into heat to slow it down.	Squealing or grinding, a soft or sinking pedal, pulling when you brake.
Steering and suspension	Point the wheels and keep the tires pressed to the road over bumps.	Wandering, pulling, clunks over bumps, bouncing.
Wheels and tires	Hold the air that holds up the car, and grip the road.	Low pressure, uneven wear, vibration.
Hybrid and electric drive	Store energy in a high-voltage battery and drive the wheels with motors.	Warning messages; high-voltage parts are for trained technicians only.

Where the energy goes

Burning fuel makes heat, and a heat engine can’t turn all of its heat into work. Some heat always has to flow out to cooler surroundings, which is why an engine needs a radiator and a tailpipe. Physicists write the engine’s efficiency as the useful work out divided by the heat put in.

In combined city and highway driving, only about 16 to 25 percent of the energy in a gasoline car’s fuel ends up moving the car. Engine losses, mostly heat, take 68 to 72 percent. Electric cars waste far less: counting the energy they win back while braking, they deliver about 87 to 91 percent of the energy drawn from the grid to the wheels.

Combined city and highway driving. Ranges are for typical cars. Sources: U.S. Department of Energy Fact of the Week #1044 and FuelEconomy.gov.

efficiency = useful work out ÷ heat put in (Eff = W / Q_h)

How the systems depend on each other

No system works alone. The engine needs the electrical system to start it, the fuel system to feed it, the cooling system to keep it from overheating, and oil to keep its parts from grinding together. The engine computer watches all of them through sensors. The brakes, steering, suspension and tires decide what all that power actually does on the road.

That’s why a problem in one system often shows up in another. A weak battery means the engine won’t crank. A thermostat that’s stuck closed makes the engine overheat. A low tire can make the car pull to one side, which feels like a steering problem. When you troubleshoot (Lesson 13), you’ll trace symptoms back across this map.

NoteYour owner’s manual is the final word

This course explains how cars work in general. Your owner’s manual and your vehicle’s service information give the exact fluids, pressures, intervals and procedures for your car, and they come first whenever they differ from anything here.

Check yourself

Tap an answer to check it, or open “Show the answer.”

In combined driving, about how much of a gasoline car’s fuel energy actually moves the car?
Show the answer
16 to 25 percent. About 16 to 25 percent. Most of the rest is lost as engine heat (68 to 72 percent).
Which part turns the pistons’ up-and-down motion into spinning?
Show the answer
Crankshaft. The crankshaft. Each piston pushes on it through a connecting rod, like your legs on bicycle pedals.
In an all-electric car, what controls the motor’s speed and torque?
Show the answer
The power electronics controller. The power electronics controller manages the flow of energy from the traction battery to the motor.
A car won’t crank, and the problem turns out to be the battery. Which system is that?
Show the answer
Electrical. The battery belongs to the electrical system, which also has to work for the engine to start.

Go deeper

U.S. Department of Energy, Alternative Fuels Data Center: How Do Gasoline Cars Work? Short diagrams of every key part of a gasoline car.
U.S. Department of Energy, Alternative Fuels Data Center: How Do All-Electric Cars Work? The same for an all-electric car.
OpenStax College Physics 2e, 15.3 Heat Engines and Their Efficiency Why no heat engine can turn all its heat into work.
U.S. Department of Energy: Internal Combustion Engine Basics How internal combustion engines work, from the Department of Energy.

Sources

I finished this lessonSaved on this device only.

A free course from Teddy Rook Book. It explains how cars work in general and follows U.S. sources; your owner’s manual and your vehicle’s service information are the final word for your car, along with state and local rules.