Slinky® Waves

INTRODUCTION

Both sound and light travel as waves, but sound waves behave in a different way than light waves. Light waves can move either up and down or from side to side. They are called transverse waves and they are the same type of waves as those you see on water. Sound waves, which are longitudinal waves, move back and forth in the direction that the sound is traveling.

MATERIALS

• 1 long length of thin rope (6-8 ft.)
• 1 Slinky®

WHAT TO DO

1. Tie one end of the length of rope around a post or door handle and hold the other end fairly tight.
2. Shake your hand up and down to make a wave in the rope. This is a transverse wave, like a water wave or a light wave.
3. Shake your hand faster and observe what happens.
4. Stretch out the Slinky® on a smooth floor and ask a friend to hold one end.
5. Holding the other end, give it a sharp push toward your friend. Notice the wave of tight coils move along the Slinky®. This is a longitudinal wave, like a sound wave.

QUESTIONS

1. When shaking the rope, what happens to the number of waves when you shake your hand faster?
2. When shaking the rope, what happens to the number of waves when you shake your hand farther from side to side or up and down?
3. What should you do to make waves in the Slinky® of higher frequency and greater amplitude?

SUMMARY

Sound waves move through the air with a squeezing and stretching of molecules of air. When a vibration is produced the air around the source of the vibration is pushed together tightly, then stretched out as the squeezed air molecules push away from each other. This motion continues and the longitudinal sound wave propagates through the air. If you watch the thin cone on the front of a loudspeaker you can see that the sounds make it bounce in and out. When the cone vibrates, it pushes and pulls the air in front of it, first squeezing the air as it pushes it and then stretching the air as the cone pulls back. If you put your hand in front of a working loudspeaker you can feel the air vibrating. When something causes an object to vibrate, the sound waves spread out as ripples of squeezed air in the same way that ripples of water spread out. The number of these high-pressure waves per second is the frequency of the sound. The amount that the air is squeezed in each ripple is the amplitude of the sound. The greater the squeeze, the louder the sound.

SOURCE

"SOUND: Science Projects." Simon de Pinna, Raintree Steck-Vaughn Publishers: Austin, 1998, p. 8-9.

© S. Olesik, WOW Project, Ohio State University, 2000.