Power

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Power is the rate in which energy converts into work. Combustion vehicles use mechanical power produced by the engine, and this power comes from the engine’s force and velocity:

power = force × velocity

Alternative fuel cars, such as gasoline-electric hybrids, must possess features that maintain power while reducing fuel use. These attributes enable alternative fuel cars to compete with traditional gasoline cars.

The engine supplies power, and the vehicle moves. The engine’s cylinders burn fuel, usually gasoline, in a process called combustion and convert the fuel’s energy into motion (the turning of the engine’s crankshaft). Regardless of the type of fuel a vehicle uses—gasoline, diesel, electricity, a fuel cell—carmakers express the vehicle’s power as horsepower, which is a unit that describes the rate at which work is done. One horsepower equals 746 watts and stands as an internationally recognized unit to measure power. (Engineer James Watt came up with horsepower in the 1700s based on his interpretation of how much work a horse could do in one minute. By Watt’s calculations, one horse could pull 330 pounds [150 kg] of matter 100 feet [30 m] in one minute: 1 horsepower = 33,000 foot-pounds per minute.) A typical vehicle uses 20 horsepower to travel at 50 miles per hour (80 km/h) for one hour. Today’s combustion engines produce 120 to 270 horsepower, a range that gasoline-electric hybrid cars and the newest prototypes also attain.

It may be hard to decide whether powerful cars preceded superhighways or superhighway systems led to more powerful cars. The following “Case Study: U.S. Interstate Highways’ Effects on the Environment” examines an often overlooked component of transportation.