Natural Science Unit 7 Laboratory Activity:
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.
- 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
- Ruler or tape measure
- Arrange the hook and pulley so that you can attach the string as shown in the diagram:
- 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.
- 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.....
- 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.
- Measure the distance between nodes.
- Record the weight used.
- 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.
- 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?
- 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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