This activity explores how sound is produced by vibrating things and causes things to vibrate.

How do we make sounds and how do we hear sounds?

• microphone
• Sound Grapher. If you don’t have a Sound Grapher icon on your desktop, go to this link and download the Sound Grapher.
• tin can, both ends open
• square plastic food storage container (leftover container)
• rubber bands
• balloons, cut open for making a drumhead
• scissors
• paper clips

This activity addresses NSES standards for physical science (for transfer of energy) and inquiry at grades 5-8
(http://books.nap.edu/readingroom/books/nses/6d.html#ps).

• Be careful not to cut your hands on sharp edges of the tin can.
• Do not make loud noises close to other people’s ears. Eardrum damage may result.

1. Make sure your computer has either a plug-in or a built-in microphone. Refer to Technical Hints to connect the microphone.
2. Turn up the input volume for the microphone.
3. Start the Sound Grapher. Refer to this link to download the Sound Grapher. It will open in a separate window.
4. The Sound Grapher shows two graphs. Click on the graph you want to use. Click on the Start button to start the Sound Grapher.
5. As you make noise, wavy lines should appear on the screen. When you click on the Stop button, the graph “freezes” the sound picture at that moment. Here is an example:
   
6. You can then switch to the other graph to look at another sound. The space bar and the Return key also run Start/Stop functions.
7. A single frequency appears as a simple sine wave. When more than one frequency is present in the sound, the waveform is a combination of several sine waves and looks more complex. It is difficult to tell what is happening from the waveform alone, so an additional analysis tool is provided. Click on the “Waves” button, and change the drop-down menu to “Frequencies.” The screen now displays the distribution of frequencies that are present in the sound, with frequency plotted on the x-axis. Here is an example. The first plot shows a sound with five major frequencies; the second sound has two major frequencies.
   

1. Sounds come from things that vibrate. A vibration is something moving back and forth in a regular way. Some things vibrate and make sounds that we can hear. All musical instruments have some part of them that vibrates and makes the musical sound.
2. You can see how sounds are vibrations by building a model. Build a balloon drum by stretching a balloon over one end of a tin can that has both ends open. Working together, stretch the balloon tight and hold it in place by putting a rubber band around the edge.
   
3. Talk into the open bottom of the tin can while touching the balloon. What does your voice do to the stretched balloon? Can you feel the vibrations coming from your voice?
4. Talk into the open bottom of the tin can after placing a paper clip on the drumhead. Can you make the paper clip move? Can you make the paper clip jump off the drum? Explain how you think the sound of your voice moves the paper clip. Be prepared to share your ideas with the class.
5. Your voice makes the drumhead vibrate up and down. These vibrations are very fast, and they make sounds that we can hear. The drum you have built is a good model of the eardrum. Draw a picture of how you think your ear works.

1. Try touching your throat when you speak or sing. Can you feel your throat vibrating?
2. Stretch two rubber bands around a plastic box as shown below. If the rubber band is very long, go around the plastic box twice to make two bands across the top.
   
3. Pluck the rubber band. You can see it vibrate. Describe the sound that it makes.
4. Make sure your computer has either a plug-in or a built-in microphone. Refer to Technical Hints to connect the microphone.
5. Turn up the input volume for the microphone.
6. Start the Sound Grapher. Refer to this link to download the Sound Grapher. It will open in a separate window.
7. Put the plastic box next to the microphone and pluck one of the rubber bands. Keep the picture of the sound by clicking on the Stop buttton. Is it a smooth sound, or a rough sound?
8. Try pulling one rubber band tighter than the other. What happens to the pitch? Which pitch is higher, the tighter rubber band or the looser rubber band?Compare the two sounds by saving one in the upper graph and one in the lower graph. Can you see the change of pitch in the Sound Grapher? You can use either the “Waves” mode or the “Frequency” mode to analyze the sound.
9. Count the number of cycles for each pitch that appear on the graph.
10. Your throat muscles pull on your vocal cords, like your fingers pulling on the rubber bands. The muscles pull less hard on them when you sing a low note, and pull harder when you sing a high note. Here is a picture of your vocal cords. The yellow part is your windpipe, which carries air from your lungs to your mouth.
    
11. Hum into the microphone. Change the loudness. What do you do to increase the loudness of your voice?
12. Hum into the microphone. Slowly raise the pitch, but don’t get louder. (This is surprisingly difficult.) The wave pattern should stay the same height, but the length of each cycle should decrease. Can you feel your vocal cords becoming tighter as you raise the pitch?
13. Make different vowels into the microphone to change the shape of the pattern. What do you do to change the quality of sound your voice makes? Is it just done with the vocal cords, or some other way?

1. Your eardrum is a piece of skin just like a stretched balloon. It vibrates when sounds reach your ear. Bones that touch the eardrum carry the vibrations to your inner ear, where they are detected and translated into signals to the brain. Here is a diagram of the ear. Can you explain why sounds aren’t as loud when you cover your ear?
   
2. Cup your ears with your hands and see if you can hear quiet sounds better. Based on what you observe, what is the purpose of your outer ear?
3. A microphone is very much like an ear. Sounds make a surface vibrate, which moves a magnetic coil that produces electrical signals. Here is a diagram. Explain which part of the ear corresponds to each part of the microphone.
   
4. Here is a diagram of a loudspeaker. It’s like an ear working backwards. It changes electrical signals into sound vibrations. How does it look like an eardrum? How does the loud speaker work like an ear in reverse?
   

• Most sounds have many frequencies in them, and not just one, even though they sound like one pitch. Use the “Frequency” mode to look at the mix of different frequencies that are in different musical instruments.
• Explore how air can make something vibrate, as it does with the vocal cords. For example, let air out of a balloon. Pinch it tight to make a pure sound. Or try blowing across a soda bottle top.
• Birds have a different vocal cord structure which enables them to make multiple sounds and very rapid changes in pitch. Do research on bird sounds: how they look and how they are produced.