Dr. Gadget's Science Machine
Here are neat ways to play with and think about sound
By Joe Laszlo
A fun look at science working in the world around you, plus a cool gadget or experiment to test it out
Associated Press
Aloha! We've been looking at the concept of sound for several columns. But before we change to a new topic, I want to leave you with a few more ideas.
The Concorde is a passenger jet that can fly at supersonic speeds, which means that it can travel faster than sound waves.
• Have you ever heard of sound waves? This is how sound moves from place to place. But sound waves are not like waves at the beach. The sounds that you hear are really only packages of energy from various sources that are using some medium to travel in to get to your ears. If there is no medium to carry the sound energy, as in a vacuum, you will not hear anything. All those space battles in the "Star Wars" movies should have been soundless!
In most instances the medium carrying the sound is air, a gas. But it could be a solid. When I was in elementary school I lived near a railroad. Sometimes I'd put my ear to the rail and I could hear the train sound long before I could see it. If you've ever been underwater, you've probably heard many sounds. Water is a good medium to carry sound energy.
• How does the sound of your voice travel in waves? The energy from your lungs is "packaged" by your vocal cords, teeth, tongue and lips. They all help to shape the sound. As the energy comes out of your mouth, it squeezes the air particles into tight packages called "compressions." But like a squashed-up spring that is released, the air wants to spring apart. It does, and actually over-springs and becomes much more spread apart than "soundless air." These are called rarefactions.
• Here's something to try: Get a toy Slinky and stretch it out between you and a friend. Then squeeze up a bunch of the coils toward yourself and then release them. You will see them spring apart as the energy moves toward the other end. If you put enough energy into it, it may come all the way back to you.
This illustrates what happens when you hear an echo. The sound energy strikes a surface and bounces back to you. Before radar, ships at sea used fog horns. The horn was blown at the same time a stopwatch was started. When the sound came back in the form of an echo, the watch was stopped, and the number of seconds were noted. With some simple calculations, the navigator on the ship could tell how far away some object, such as a cliff, was from the ship.
• Have you heard of planes traveling at supersonic speeds? What does supersonic mean? It means faster than sound. For the Concorde to travel faster than sound, it must be going at least 760 miles per hour. The Austrian physicist Ernst Mach realized that if something traveled faster than sound, conditions would be very different than with regular subsonic travel. For this reason, traveling faster than sound is called the Mach number. If you are going Mach 2, this is two times the speed of sound.
• Have you ever watched a baseball game from seats in center field? The pitcher winds up and throws the ball. The batter swings, drops the bat and starts running toward first base. Then you hear the crack of the ball hitting the bat! Why was there such a difference between what you saw and what you heard? Very simple: Light travels faster than sound — 880,000 times faster.
In my next column I'm going to begin discussing light. It also travels in waves — light waves! Until then, a hui hou!
Correction: The speed of light is 880,000 times faster than the speed of sound. A previous version of this story was incorrect.
"Dr. Gadget's Science Machine" is written by Joe Laszlo, a retired science teacher.
