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Home School Life Journal
"Let us strive to make each moment beautiful."
Saint Francis DeSales
painting by Katie Bergenholtz

What Things Affect Sound?

We performed a series of sound experiments. First I took a board (6 inches by 18 inches, 1 inch thick), several weights of fishing line and 3 2-liter bottles ( you could use 1/2 gallon plastic milk jugs) and 3 screw eyes (size 14). Screw one screw eye in the middle of one end of the board. Screw in one of the other screw eyes on either side. This is the set up for all three experiments.How does thickness affect a line's sound?
In the first experiment, tie 3 feet of 50pound test weight fishing line to the first screw eye. Tie 3 feet of 30 pound test weight fishing line to the middle screw eye and 8 pound test weight fishing line to the last screw eye. Tie the other end of the fishing lines to the bottles. Fill each of the bottles with 2 cups of water. Position the board so that the end opposite the screw eyes is even with the end of the table. Let the bottles hang over the edge of the table.
Pluck each line and compare the sounds.
The heavier the weight of the line, the lower the sound will be because it has more weight to move and therefore is slower. Slower vibrations equal lower sounds. How does tension affect a line's sound?
For the second experiment, remove the 30 and 8 pound weight pieces of fishing line and replace them with two more 3-foot pieces of 50 pound weight line. Tie lines to the bottles as before but this time, leave one with the 2 cups of water, but add 1 more cup to one (for a total of 3 cups ) and 3 more cups to the last one (for a total of 5 cups). Arrange as before, with the bottles hanging over the edge of the table. Pluck each line. Do they sound different?
Increasing the weight stretches the line tighter, increasing the tension. A tighter string springs back faster to its original position, producing a higher pitch (and frequency).
How does length affect a line's sound?For the last experiment, you can keep the setup the same as the last experiment. You just press one of the strings down with one finger, and pluck with the other. Press the string down at a different point, and pluck it again. How does the sound change?
The shorter the length of the string, the higher the sound results. Because the vibrations have to travel through the string to produce the sound, the longer the string, the longer it has to travel. This longer traveling, slows down the vibrations and lowers the pitch.
So what did we learn?
How thick a line is, how tightly it is stretched and how long the line is are all factors that affect sound. We will be using this information when we build our own musical instruments.
More neat sound experiments:


  1. You guys have been busy with sound!

  2. I loved your sound experiments, too.


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