Using Physics to Explain the World
GPS, Smoke Detectors, Hybrids, Electronic Noise and Heated Glass
Much of the technology in our world seems mysterious and almost magical. However, elementary physics explains everything from GPS to hybrid cars to smoke detectors.
GPS, or Global Positioning System, has been considered one of the wonders of the modern world. For only about one hundred dollars, one can buy a cheap device that can still locate its own position anywhere in the world. The technology works by receiving signals from multiple satellites orbiting Earth. These satellites orbit in MEO – medium Earth orbit – which means they go around the world every 12 hours and stay about 12,000 miles above Earth. There are 24 GPS satellites, all of which know their own location. The handheld device receives signals from two or more of these satellites, then calculates its own position based on the distances from each point of reference given by the satellite.
Smoke Detectors
The most frequently used smoke detectors actually use radioactivity. A small radioactive source under the cover emits alpha particles, which knock electrons off the surrounding air molecules. These alpha particles only travel about 1 centimeter and make the air in that area electrically conductive. The battery measures this conductivity; it does not sound at normal levels.
However, if there is smoke drifting under the cover, the electrons stick to the smoke particles and are no longer able to move freely. This makes the electric current stop. When the battery detects the lack of electric current, it sets off the piercing shriek of the alarm. This is why the strength of the battery is so important; be sure to change the battery frequently.
Hybrid Cars
As hybrid automobiles grow in popularity, it is worth knowing how the new Toyota Prius is saving money on gasoline. The cars use a small gas engine to charge a battery which provides the energy for the car. Therefore, the gas engine can run at a stable, constant rate; it is two to three times more efficient than the engine in ordinary cars. Also, extra speed and other mechanical motion of the car can be converted into stored chemical energy in the rechargeable battery. Hybrids do this instead of using brakes, which can only turn the energy of motion into heat. As the car batteries improve in their storage capacity and efficiency, the automobile industry will continue to dramatically change.
Electronic Noise
Radios tuned between stations give out a hissing sound. Old television sets show white spots moving around the screen, popularly known as snow. These two electronic phenomenons are due to electrons jumping around. Due to heat, they are in constant motion, and when there is no other signal to receive, all that is visible or audible are the moving electrons. The way to reduce the movement is by lowering the temperature; highly sensitive electronics need to be cooled to reduce the hiss and snow.
Heated Glass Cracking
Pyrex revolutionized the glass industry because it was the first glass that would not crack after being heated and then rapidly cooled. Sudden temperature changes usually cause glass to break or shatter. Glass does this because the outside cools faster than the inside does, causing it to bend. Glass is too brittle to bend, so it breaks. It does not happen when initially heated in the oven because when glass is heated slowly, the heat passes through the glass and warms the entire thing uniformly.
Sources
Muller, Richard A. Physics for Future Presidents, Spring 2008 Edition. Mason: Thomson, 2008.
