Fun with Physics [antikvár]

sal TITLE PAGE: Water sprays Jamila Jones, 13, of Oatiland, California, as she launches a toy rocket. Powered by water and compressed air—and following principles of Isaac Newton's third law of motion—the rocket climbs. Discover on pages 94 and 96 how these principles help to move racing balloons—and you! \ Introduction "All aboard!" You've been standing in line for half an hour, gripping your ticket and listening to the whoops and screams of the roller-coaster passengers overhead. Now it's your turn. You settle into your seat. The car lurches forward. A chain pulls your car to the top of the first steep rise. At this moment, you're probably not thinking about physics. But watch how many examples of physics you'll experience—and don't worry about all the terms in bold type. You'll hear more about them later. The moving chain runs on electricity. By pulling you to the top of an incline, the chain converts electrical energy to gravitational potential energy—stored energy you have when you're in a position to fall. Then gravity tugs on you. You're swooping down the steep incline, converting your potential energy to kinetic energy—the energy you have when you are moving. At the top of each incline, you feel weightless. That's because your inertia keeps your body going up momentarily as the car hurries downward. Suddenly, the car enters a steeply banked turn. You feel as if you might be tipped out of your seat. Actually, the tilted track forces the car to turn, pushing against the car with centripetal force. If it weren't for the tilt, your car would go straight and jump the tracks. Whooaa! The car enters a loop and you're upside down! You have to travel fast for this to work. Why don't you fall out? Inertia and centripetal force are at work again. Inertia tries to keep you moving outward in a straight line. The track acts against inertia with centripetal force and pushes the car around in a circle. Inertia presses you into your car, even when it's upside down. Now the inclines are getting smaller. The roller coaster is slowing down. Friction works to slow you to a stop. Whew! If you like roller coasters, then you felt right at home on this ride. But did some of the terms in heavy type look like Greek to you? They refer to principles of physics. Actually, many physics terms come from Greek. The word "physics" itself comes from a Greek word meaning "nature." Physics is the study of energy and matter—and that covers just about everything under, and including, the sun. If physics does not seem to relate to you, just think: Physics explains sound to musicians, color to artists, jumping to basketball players, speed Thrill seekers feel weightless for a split second at Six Flags Over Texas, a park near Dallas. At the top ofthe hump, riders keep going up for a bit after their car has headed down. That's because of inertia, which you'll read more about on page 38.