72 Perpetual Motion: Fact or Fiction?-High

Perpetual Motion: Fact or Fiction FOCUS? Question Is perpetual motion possible?

A Machine That Never Stops Have you ever used a gyroscope? It is like a top. You pull a string, and then it spins for a very long time. Is it possible to make a gyroscope spin so fast that it never stops? If so, it would be in perpetual (per-PEH-chew-uhl) motion. A perpetual motion machine is a device that moves forever, without adding energy. But can such a machine exist? The blades of a wind turbine may seem to be in constant motion, but the turbine is not a perpetual motion machine. Wind is made of air particles that have kinetic energy, the energy of motion. When the moving air blows against the turbine blades, some of the energy moves the blades. If the wind stopped, so would the turbine.

Why would we want a perpetual motion machine? We need large amounts of energy to run our phones, cars, and other machines. To produce energy, we burn fossil fuels such as coal, oil, and natural gas. We also use wind farms, dams, and nuclear power plants. These energy sources often create pollution or disrupt environments and ecosystems. If we could invent a perpetual motion machine, it would keep moving without adding energy. In fact, its motion could be used to produce more energy. Just imagine... free, clean energy!

An Object in Motion... Unfortunately, no one has ever successfully designed a perpetual motion machine. Newton's first law of motion says that an object in motion will stay in motion unless it is acted on by outside forces. This seems to mean that perpetual motion should be possible. In the real world, however, outside forces always interfere. When a baseball is hit into the air, the forces of air resistance and gravity act on it. Air resistance is a kind of friction that slows objects moving through air. Gravity pulls the ball down to the ground.

Gravity Machines Gravity is the force that attracts objects toward each other and toward Earth's center. Because this force is always present on Earth, people have tried to make perpetual motion machines using gravity. In the machine on this page, gravity pulls the lifted ball downward. It collides with the other balls, and the last ball flies upward, until it is pulled down again by gravity. Does this machine convert gravity into perpetual motion? It may seem like it, but no. As kinetic energy travels from one ball to the next, friction slows the movement slightly. The energy from the initial human pull to get the machine moving will eventually run out because of friction.

Frictional Forces Friction is a force caused by two objects rubbing together. Friction changes kinetic (moving) energy to thermal energy, or heat. Think about rubbing your hands together very quickly. As you use kinetic energy to move your hands against each other, they get warm. The warmth is thermal energy caused by friction. In every machine, friction eventually "steals" enough kinetic energy to make the machine stop. Friction changes some of the energy of motion into heat energy. Then the heat energy is transferred into the air or nearby objects. If the design is very good, there will be very little friction, but no machine runs forever without needing more energy.