Pulley and Weights Sounds in Strings (Teresa Glass)

Author

Teresa Glass Arleta High School

Principles

Shortening a string makes the pitch higher, lengthening the string makes the pitch shorter. Then speed of sound is equal to its frequency measured by its wave length.

Sensor / Probe

The sensor probe I used for this was Audio Frequency by Keuelsoft. It measures sounds in hertz using sound waves. The sensor is like an oscilloscope.It comes from the Google Play store.

Standards

Materials needed

Pulley, wire, clamp, weights, mobile phone sound app.

Procedure

1.Carefully mount a pulley over one end of a table. Securely clamp the end of a string to the other end of the table.

2. Tie the end of the string around a mass hanger. lay the string over the pulley. Place a pencil under the string near the clamp, so the string can vibrate without hitting the table.download a mobile phone app that measures sound.

3.Hang one 500-g mass on the mass hanger. Pluck the string, listen to the sound, and observe the string vibrate..

a. Record your observations in a table with length load and Pitch. measure sound with phone app. and record results on table. Take a picture of this measurement with your mobile phone,

4.Use a key or some other small metal object. Press this object down on the string right in the middle , to hold the string firmly against the table. Pluck each half of the string.

a.Record the result in your table.Repeat measuring the sound with your phone app and taking a picture of it.

5. To change the string length, press down on the key in different places. Pluck each part of the string.

a. Record the result in your table. continue measuring the frequency of sounds with your phone app.

6.When you pluck your string it does not move at the ends.Measure the length of your string and find the wave length of the vibration for each string length.

a. Record the wavelength in your table.

b. Look over the data in your table. Make a general statement about what happens in the pitch you hear as you change the length of the string.

7.Remove the key, so the string is its original length. Pluck the string. To investigate the effect of tightening the string, add a second 500-g mass to the mass hanger. Pluck the string again, observe the vibration, and listen to the pitch of the sound.

a. Make up a table to record the data in your log.

b. Add a description to the pitch of the sound to your table. Continue adding weights and observing the sound until the total mass is 2000 g.

c. Look over your data. As the same mass increases the string becomes tighter, and its tension increases. Make a general statement about what happens to the pitch you hear as you change the tension in the string.

Explanation

Shortening the string made the pitch higher. Increasing the length of the string made the pitch lower. Increasing weights on the string makes the pitch higher because it increases the tension on the string. Decreasing the weights on the string made the pitch lower because the tension on the string was decreased.

Questions

1. What happens to the pitch of the string when you decrease its length? The pitch goes higher.

2. What happens to the pitch on the string when you increase its length?The pitch goes lower.

3. What happens to the pitch on the string when you increase weight and tension/ the pitch goes higher.

Everyday examples of the principles illustrated

In tuning a guitar or violin, the performer changes the string tension by turning a peg attached to one end of the string. As the peg pulls the string tighter, the pitch goes up.

Photos

Audio frequency Counter app from Google Play Store acts as oscilloscope on your mobile phone.

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Movies

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References

http://www.californiascienceteacher.com/classes-taught/ics/index.htm

American Association of Physics Teachers(2004)Integrated Coordinated Science for the 21st Century.Armonk, New York:It's About Time.

www.itsabouttime.com