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Science:  Speed of Sound
by:  Tom Kuntzleman
Grade Level:  8
Purpose:  To determine the speed of sound.

Materials: Tuning forks, graduated cylinders, water, rulers with centimeter markings.

Introduction: Sound is a wave. The speed of any wave can be found with the equation:

speed = frequency x wavelength

The wavelength of a sound wave can be found by allowing the sound wave to pass near a tube. When the length of the tube is one-quarter the wavelength, the sound wave will resonate. This means that the sound wave will get stronger (louder) By finding the length of a tube that causes a sound wave to resonate, the wavelength of the sound wave can be calculated. If the frequency of the tuning fork is known, the equation above can be used to find the speed of the sound wave.

Procedure:

1. Put some water into a 100 mL or 500 mL graduated cylinder.

2. Tap a tuning fork on a soft object and place the fork near the opening of the graduated cylinder.

3. If the sound resonates (gets loud), proceed to step 5.

4. If the sound does not resonate, either add or remove water then to back to step 2.

5. Measure the distance in centimeters from the top of the water level to the top of the graduated cylinder. Record this distance.

6. Convert the distance in step 5 to meters.

7. Multiply the distance recorded in step 6 by 4. This will give you the wavelength of the sound wave.

8. Now look at the tuning fork you used. There should be a number printed on the tuning fork. This number is the frequency of the sound wave.

9. Using speed = frequency x wavelength, calculate the speed of the sound wave. Your answer will be in units of meters/second.

10. Repeat the experiment using different frequency tuning forks. You should get the same speed for different tuning forks.

11. Have students search the internet to see if they can find the speed of sound. Some links will have equations for the speed of sound at various temperatures. Most students usually find the speed of sound in this experiment to be around 345 m/s.

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