Can Sound Travel through a Barrier?
Talk It Over
Sound is vibration. The sounds that reach your ears travel as vibrations of the air. Can you hear sound through a barrier? Does a barrier affect how far away you can hear a sound?
- Outdoor space to work in
- Ball of white string
- Tent stake for soft ground (or tape for a paved surface)
- 1 or more willing listeners
- Jingle bell
- Colored markers: black, red, and blue
- Large piece of cardboard
- Sharp scissors or knife
- Flexible, metal measuring tape (the kind carpenters use)
- Find a large area outdoors where you can work. A grassy area in a park or a ball field is good, or you can use a paved playground.
- Tie the string to the tent stake and put it into the ground at one end of your workspace. (If working on pavement, tape the string to the surface).
- Ask a willing listener to stand at the tent stake (or tape) and wear a blindfold.
- Tie the jingle bell to your finger. Ring the bell so the listener recognizes its sound.
- Instruct the listener to raise a hand whenever he or she hears the jingle bell.
- Start backing away from the listener, holding the loose end of the string in one hand and ringing the bell with the other. Every 1 or 2 meters (1 or 2 yards), ring the bell. Keep backing away, letting out more string and ringing until the listener no longer raises a hand.
- Flatten the string along the ground and make a black mark on it at that point. The black spot marks the limit at which the listener can hear the jingle bell.
- Now return to the listener and repeat steps 5–6, holding the piece of cardboard in front of the bell, between you and the listener. When the listener no longer raises a hand, flatten the string along the ground and make a blue mark. The blue spot marks the distance at which the listener can hear the sound through the cardboard.
- Ask an adult to use the scissors or a knife to cut a hole about the size of a quarter in the center of the cardboard. Repeat the experiment, holding the bell just behind the hole. Put a red mark on the string to indicate the distance at which the listener can hear the sound through the hole.
- Using the metal measuring tape, measure the distances along the string to the black, blue, and red marks. Enter them in your data table under "Listener 1." Repeat the experiment with as many listeners as you can find to help you with your project. Use new string each time.
- Calculate an average of all listeners for all three distances.
Don't perform this experiment in a parking lot or in the street. Don't try to cut the hole in the cardboard yourself. Get an adult to help.
Use the "Go" procedure with two or three listeners, but don't calculate an average. Get an adult to help with the marking and measuring.
Sound waves vary in their frequency and amplitude. Frequency determines pitch. Amplitude determines loudness.
The jingle bell is a high frequency, low amplitude sound. Try the experiment with sounds of different frequencies and amplitudes. Also try substituting other barrier materials to see how they interact with different frequencies and amplitudes. You might also experiment with holes of different sizes and shapes. Or try several holes arranged in different patterns to see whether they impede or improve the average hearing distance.