Let’s be critical. Fill a plastic bag full of water. Seal the bag and listen through it by placing your ear against its surface. Which type of matter did the sound have to travel through in order to reach your ear?
solid; b) liquid; c) gas
If you answered “liquid,” you’re only partially correct. The sound was also carried by the solid plastic covering.
Things Required:
Wristwatch (old wind-up type)
Large plastic sealable bag
Directions:
Wind up the wristwatch. Make sure it works. Place the watch on a flat surface. Position your ear about 6 inches above the watch. Can you hear it tick?
Fill a plastic bag with air and seal it shut. Place the bag over the watch. Place your ear on the surface of the bag. Can you hear the ticking now? Why?
This Is What Happens:
Without the bag, the ticking sound was transferred only by air. Since air particles are very spread out, this type of transfer is not effective.
When the bag full of air was used, things changed. The ticks were absorbed by the plastic skin of the bag. The sound energy was then transferred by the plastic particles along the surface of the bag. Since the particles of this solid were concentrated, less sound energy was lost. This produced a volume that was loud enough to detect.
But don’t forget; the total sound also depended upon what was in the bag. In this case, it was air.
