Heat engines, including car engines, take energy from being warm compared to the surroundings and turn it into motion. Only about 12%-30% of the energy in a conventional car's fuel moves it down the road, as of November 2026. In a gas car, the water pump, fuel pump, oil pump, ignition system and engine control system use energy made by the engine. EVs convert over 77% of the electrical energy from the grid to power at the wheels, as of November 2026. 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.

A piston engine only delivers power during a stroke, so a flywheel keeps power flowing to the drive train steadily. Most gas engines are four-stroke engines, which need four piston strokes to finish one cycle. In the power stroke, the burning gases push the piston. A spark plug lights the fuel in a gas engine, and a spark plug has no moving parts. Modern car engines use computer-controlled fuel injectors to adjust the fuel-air ratio.

Two types of electric motors are used in electric vehicles: the direct current (DC) motor and the alternating current (AC) motor. An electric motor changes electrical energy into motion. A differential lets the wheels spin at different speeds while both are still powered, as when a car turns a corner. One electric car layout uses a single large electric motor coupled to the rear wheels through a differential housing. Another layout uses two smaller motors that power each wheel separately through independent drive shafts. An electric car's motor stops when the car stops, so it does not idle.

A hybrid electric car has both an internal combustion engine and one or more electric motors. Parallel plug-in hybrids connect both the engine and the electric motor to the wheels. In a series plug-in hybrid, only the electric motor turns the wheels, and the gasoline engine only generates electricity. In a hybrid car, an electric generator makes electricity from the rotating wheels while braking and sends it to the traction battery pack.

The idea of a brake that stores the energy it absorbs for later use dates to the late 1800s. 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, but electric cars all but disappeared from U.S. roads by 1935.

Words to know

• flywheel: energy-storing wheel
• differential: wheel speed gear
• hybrid: engine-motor car
• generator: makes electricity
• stroke: one piston move