Greentech Media

Of all the forms of energy, mechanical energy is probably the easiest to understand-just try lifting a heavy suitcase. Thus the traditional unit of mechanical energy is the foot-pound (ft-lb), the amount of work required to move a one pound object through a distance of one foot. One foot-pound equals about 1.36 J. The metric analogy to the foot-pound is the newton meter (N·m). One newton meter equals one joule.

Probably the most familiar unit of mechanical power is the horsepower (hp), conceived by James Watt in 1782 to position his steam engine against the competition. Watt determined that an "ideal" mine pony could lift a 33,000 lb bucket of coal one foot in one minute and defined mechanical horsepower accordingly.

Although 33,000 ft-lb/min sounds like a lot, the horsepower is a relatively small unit, equal to about 746 W. A toaster oven draws about 1,000 W (1.3 hp), and it takes at least 5 hp just to spin the blade on a power lawnmower. The four-cylinder engine in a 2007 Honda Accord sedan generates 166 hp; the 12-cylinder engine in a new Rolls-Royce Phantom produces 453 hp.

Greentech companies are addressing mechanical energy issues on multiple fronts. Biofuels, hybrid gasoline/electric engines, plug-in hybrids and other technologies reduce the amount of greenhouse gases produced in the creation of mechanical energy. They also help to wean automobiles and other machinery from fossil fuels. The hybrid engine in a Toyota Prius uses less gasoline than a conventional engine because its internal combustion side generates only 76 hp.

Materials research is further reducing mechanical energy costs. Remember, work equals weight times distance. As much as 50 percent of the Boeing 787 Dreamliner is made of lightweight composite materials. This, along with increased engine efficiency, allows the 787 to use 20 percent less fuel than other airplanes of similar size.