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Natural Science Unit 7 Laboratory Activity:
Sound

Goal: To measure how vibrations on a string produce sound at different pitches.

You can create a standing wave on a string by adjusting the tension or the vibration. A standing wave will have nodes at each end of the string, and one or more nodes at intervals along the string.

Materials and Equipment:

• Tuning fork or other source of constant known vibration; if you have multiple tuning forks, you can compare more data. If you have trouble getting this to work with a small tuning fork, try using a hand massage vibrator.
• String
• Hook or some point to which you can affix one end of the string
• Pulley (or other smooth edge that string can slide over; something with teflon coating will work) over which you can drop string
• Spring
• Cup
• Weights
• Ruler or tape measure

Procedure:

1. Arrange the hook and pulley so that you can attach the string as shown in the diagram:
   
2. Tie the spring to the end of the string and attach a cup or other container to which you can add weights to change the tension on the string.
3. Touch the vibration source to the fixed end of the string near the hook so that the string vibrates. You will probably have to do this several times as you.....
4. adjust weights until you have the right tension to create a standing wave on the string with one node at each end and no nodes in the middle.
5. Measure the distance between nodes.
6. Record the weight used.
7. Repeat the process, but change the tension by increasing the weight pulling on the string until you get a node at the midpoint. Try to get two and three nodes.

Data Analysis:

• Record the mass, the number of nodes, and the wavelength. Remember that a complete wave starts at node #1, then goes up (or down) to a midnode at ½ wavelength, then goes down (or up) and returns to a third node position at full wavelength.
• Is there a connection between wavelength and tension (represented by mass)? If we double the mass, what happens to the wavelength?

Report:

• Lay out your data in a well-organized table.
• Show at least one set of calculations, and the results of all calculations in the table.
• Predict what will happen if you shorten your string. What sounds will you be able to produce?

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