ONE of Sir Isaac Newton's three famous laws of motion is that "things in motion tend to stay in motion."
For thousands of years, flywheels have taken advantage of this law. Potters could give an occasional kick to keep a stone wheel in motion, while their hands worked dexterously to mold a spinning mass of clay.
Some experts say the time may be ripe for the flywheel to find its way into a host of new applications, aided by technological advances of the last 20 years.
Perhaps the most exciting possibility is using flywheel-based batteries to power electric vehicles. The flywheel could do a better job of storing and unleashing power than current electric batteries do.
The flywheel could also be used in applications such as stationary systems that would enable electric utilities to store power for use during times of peak demand or as an efficient means of storing solar energy.
"We've been identifying the size of the potential market and it's absolutely staggering," says Edward Furia, president of American Flywheel Systems Inc. of Bellevue, Wash., near Seattle. The start-up company has been flooded with inquiries from potential partners and from the news media since it announced a flywheel patent this past summer.
Critics say the price tag will be a barrier to widespread use.
"We're a long way from having these devices, and we're even further from having them at a reasonable cost," says Mark Ross, a physics professor at the University of Michigan in Ann Arbor, Mich. Still, he says, the flywheel "has very good potential."
Mr. Furia says the price will become attractive with mass production. The first order of business, however, is to actually build the device. American Flywheel Systems, known as AFS, will work with a major defense contractor this year to build a prototype and expects to have it in an automobile by the end of 1994.
Flywheels are already used in automobiles to translate the intermittent power produced by the combustion engine into steady power to the wheels.
For the flywheel to replace gasoline as the actual power source, the big challenge is to achieve a high "storage density" of energy. The heavier the wheel, the faster it spins, and the less friction there is, the more energy is stored.
"How much energy can you put into this square-foot box that contains a spinning wheel?" asks Professor Ross.
Plenty, according to Furia. AFS estimates that with 20 flywheels, each nine inches in diameter and weighing about 30 pounds, a car could go 300 to 400 miles between rechargings. The vehicle could accelerate from 0 to 60 miles per hour in 8 seconds.
THE flywheels would reach speeds of up to 200,000 rotations per minute. To "spin them up," electric current would be injected from an outside source, just as gas is pumped into a car. The electric current, after entering "pickup coils" in the flywheel housing, pushes magnets in the flywheel spokes, causing the wheels to spin.
The spinning magnets then generate electric power that can be drawn off on demand through the same pickup coils until the wheel is "spun down" and needs recharging.
The ultrahigh speeds that AFS predicts for its system are made possible by advances in composite materials and magnetic bearings.
Not only can composite materials (such as graphite) withstand the stresses created by the rapid spinning, but if they fail they dissolve into a harmless fluffy substance that Furia likens to cotton candy, while a metal wheel might break into dangerous shrapnel.
Each flywheel battery, in the AFS design, would actually contain two flywheels, sitting side-by-side and spinning at precisely the same speed in opposite directions around a stationary shaft. This design is intended to counteract the gyroscopic force that one wheel alone would create.
Magnetic bearings will allow the wheels to spin suspended in a virtually friction-free environment, rarely touching the stationary shaft. A vacuum housing further cuts friction by removing air.
In addition to permanently operating magnetic bearings, the device would have active magnetic bearings that would counteract G-forces as the vehicle goes around curves.
The AFS-patented technology was developed by Jack and Steve Bitterly, a father-son team of aerospace scientists. Furia, an attorney and former Environmental Protection Agency official, is leading the effort to find partners such as electric utilities, defense companies, and other firms with capital and expertise to invest.
The partnering goal is well-suited to an era when many defense companies - facing Pentagon budget cuts - are eager to throw their technological expertise into commercial applications.
THE timing of AFS's effort is also propitious: California and other states are demanding "zero-emission" vehicles on the market by 1998.
Carmakers have focused their efforts to date on improving traditional chemical batteries. In 1991, they formed the Advanced Battery Consortium, also funded by the federal government and electric utilities, to do research and development in this area.
While the flywheel has the potential to leapfrog past more-traditional batteries, so do some other emerging technologies such as supercapacitors, thin-film batteries, or fuel cells.
"I think that's ultimately an ideal answer," Ross says of the fuel cell, which creates electric power with a simple electrochemical reaction of hydrogen and oxygen. But, he adds, "again, we're quite far away from having a cost-effective device."
AFS, meanwhile, is not the only flywheel developer. Other companies and researchers have their own versions. So Furia is trying to build interest in the AFS system. But, he says, "it's a very big technology, and there's room for a lot of players."
Some players see flywheels as a supplementary - not primary - source of power in electric cars. Such "hybrid" cars would run mostly on a more-traditional battery, while a flywheel battery would be used when rapid acceleration was needed.
Ross says he thinks the flywheel is likely to start in this backup role rather as the sole power source in a car.
Richard Post, a scientist at the Lawrence Livermore National Laboratory in Livermore, Calif., says both options are feasible but that economics may cast the flywheel in a supporting role in a hybrid car, because fewer of them would be needed in each vehicle. But he adds that once flywheels get into mass production, "I don't see anything intrinsically expensive" about them.
Dr. Post notes that the automotive application of the flywheel is more difficult than stationary applications. He intends to build and install a flywheel system as a backup power source for a computer system by October.