Hanging Around with Sound: Make Your Own Secret Bell!
Have you ever tried making “walkie-talkies” using a long piece of string and two tin cans? If you have, you know that they work surprisingly well—at longer distances you can hear people better through the cans and string than you can through the air!
In this activity we're going to use the same concepts to build a personal bell, one that makes sounds that only you can hear!
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
If you've ever been near a speaker with a loud bass (or heard a car drive by with the radio turned up), you may have experienced the “buzzing” feeling in your body caused by the loud noise. This isn't your imagination; the sounds we hear are actually vibrations traveling through the air—or through other materials, as we'll observe in this activity.
Most of the sounds we hear come to us through the air. When your friend calls your name, your friend's vocal chords cause vibrations in the air, which travel through it as a sound wave and arrive at your ears. Sound waves, however, can travel through other materials, too, and in fact many materials are much better than air at transmitting sound! You can experience this for yourself by gently tapping a metal fork or spoon against a countertop, and listening to the sound. Next, put your ear to the countertop and tap the counter again with the fork or spoon. The sound should be much louder, because the counter is better than air at transmitting the sound vibrations caused by the tapping!
The difference in how well a material can transmit sound is determined by the material's density, or how closely packed the molecules (that make up the material) are to one another. Imagine a row of dominoes. If the dominoes are far apart, one or two of them can fall over but the rest will remain standing. If the dominoes are close together, one domino falling over will bump into the next one, which will bump into the next one and the dominoes will fall down in a traveling wave. This is similar to how a sound wave travels; if the molecules are close to one another, they will bump into together more often and the vibration will move through them more efficiently. Solid objects such as metal desks and even string have molecules that are packed together much more closely than are the molecules in air.
Extra: With your index fingers still pressed against your ears, try banging the hanger against something hard, then grab the strings right in the middle of the sound. How does holding the strings change the sound you hear?
Extra: Repeat the activity using another metal household item, such as a cooling rack, metal salad tongs or a butter knife. How does the sound change with the different items?
Observations and Results
When the hanger was hanging freely from your fingers, did you notice that the sound produced by tapping against it had more resonance (a deep, full, vibrating quality of sound)? It should have sounded more like a bell or gong when it was hanging from the string compared with when you held it or pressed it against your ears and tapped it.
Why did you hear different things? As we discussed in the background, sound vibrations can travel more easily through some materials than others. When the hanger assembly was hanging freely in front of your body, tapping the hanger caused it to vibrate. These vibrations traveled up the string and into your fingers, then through them into your head. When you held the hanger away from you and tapped it, the vibrations traveled through air to get to your ears. From this activity you can tell that the string and your fingers are much better sound transmitters than the air around you!
When you were holding the hanger against your ear with your hand, the hanger couldn't vibrate as much (because you were holding it in your hand). Therefore, the sound was muted because fewer vibrations were produced. Holding the strings with your hands when you swung the hanger would have a similar affect. The strings couldn't vibrate as much, and therefore the sound waves were not transmitted as efficiently to your ears.
More to ExploreTalk Through a String Telephone, from Scientific American
Outer Space, the Silent Frontier: An Experiment on Sound Waves, from Science Buddies
What Material Makes the Most Resonant Soundboard?, from Science Buddies
Amazing Resonance Experiment!, from Illusions Science
Science Activity for All Ages!, from Science Buddies
Megan Arnett, PhD, Science Buddies
Science Buddies |
Sound waves, vibration, hearing
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