In the compression stroke, the piston squeezes the fuel-air mixture into a smaller space. Compressing the fuel-air mixture takes work, just as inflating a bicycle tire with a pump takes work. A spark plug lights the fuel in a gas engine, and its spark needs high voltage, anywhere from 40 kV to 100 kV. A diesel engine takes in only air, compresses it, and then sprays fuel into the hot air to make it ignite. Spark plugs are part of gasoline engines but not diesel engines, because diesel is ignited by compression.

The crankshaft turns the up-and-down motion of the pistons into spinning motion. The Wright brothers' 1903 engine had four cylinders, with each piston connected to a common crankshaft. Early gasoline cars had to be started with a hand crank. A starter motor replaced the hand crank on gasoline cars in 1912 when an electric starter was introduced.

In a gas car, the transmission passes the engine's power on to the wheels. A gearbox lets a gas engine run at efficient speeds no matter how fast the car is going. A differential lets the wheels spin at different speeds while both are still powered, as when a car turns a corner. In a rear-wheel drive car, the drive shaft sends power to the drive axle, which holds a final drive gear and a differential. A rear-wheel drive car has a long, thin drive shaft running the length of the car to the rear differential. Most electric vehicles do not use a multi-speed transmission; the motors are usually single speed.

An electric car has a charge port, and the onboard charger changes incoming AC electricity from the charge port into DC power for the battery. When an electric car's battery is charged, some energy is lost in changing AC power from the grid into DC power for the battery. An electric car also has a small auxiliary battery that powers the car's accessories. The DC/DC converter changes high-voltage DC power from the traction battery to the lower-voltage DC power that runs accessories and recharges the auxiliary battery. An electric car has a thermal system that keeps the motor, power electronics and other parts in a proper temperature range. A typical electric car battery pack may last 12 to 15 years in moderate climates and 8 to 12 years in severe climates, according to a DOE study cited as of November 2026.

The electric car came from a series of 1800s breakthroughs, from the battery to the electric motor. The first successful electric car in the U.S. appeared around 1890. By 1900, electric cars made up around a third of all vehicles on the road. The electric Lunar rover became the first manned vehicle to drive on the moon in 1971.

Words to know

• compression: squeezing
• diesel: fuel-igniting engine
• differential: wheel speed gear
• crankshaft: spinning engine part
• converter: power changer