Hybrid Car Quiz

Although there are diesel-electric buses on the road -- and nuclear-electric submarines underwater -- most hybrid cars combine a gas engine with electric power. The two most common types of gasoline-electric hybrids are parallel and series hybrids.

In a parallel hybrid, both the gas engine and the electric motor connect to the transmission and can turn the wheels. Typically, the engine is smaller and more efficient than what you'd see in a gas-powered car.

A series hybrid uses a gas engine to turn a generator. The generator can charge batteries or move the wheels. Either way, the gas engine never directly powers the vehicle.

It may seem like a bigger engine can do more work, but smaller engines tend to be more efficient. They're lighter, so it takes less energy to move them. The same goes for their pistons -- they're lighter and take less force to move. Smaller cylinders also require less fuel.

The typical hybrid car's electric motor is more advanced than an ordinary motor. For example, as you accelerate, the motor can pull energy from the batteries to make the car go faster. But when you slow down, it can act as a generator, recharging the batteries.

Regenerative braking is one of the many tricks most hybrid cars use to get the most out of a tank of gas. The motor acts as a generator, using the energy from braking to recharge the batteries.

The Prius cuts down on emissions by using the electric motor to get the car going and accelerate up to about 15 MPH. Then, the gas engine takes over and drives within a narrow band of speeds.

The power split device in a Prius is a gearbox that connects the engine, generator and electric motor. It lets the car operate as a parallel or series hybrid, depending on the needs of the moment. On top of that, it acts as a continuously variable transmission.

The two main benefits of a hybrid car -- cutting down on emissions and improving gas mileage -- are interwoven. Because you're using less fuel, you're putting out fewer emissions.

When a hybrid car slows down, the engine does some of the work. It acts like a generator, recovering energy for the batteries. If you stop too suddenly, your brakes do most of the work, and your batteries don't get the extra charge.