Bell Jar (Anna Tavitian)

Author

Anna Tavitian, AGBU Manoogian-Demirdjian School

Principles

Mechanical Waves - Sound Waves

Standards

PS4.A: Wave Properties

• A simple wave has a repeating pattern with a specific wavelength, frequency, and amplitude. (MS-PS4-1)

• A sound wave needs a medium through which it is transmitted. (MS-PS4-2)

Materials needed

• A glass jar

• Bell

• Vacuum pump

• Battery

• Wire, insulated, with alligator clips (2)

Procedure

1. Use the alligator clips to attach one wire to each side of the bell jar.

2. Attach the free ends of each wire to one terminal of the battery.

3. Connect the free end of the other wire to the second battery terminal.

4. Observe the sound of the bell and see what is happening in the bell jar.

5. Attach the vacuum pump to the bell jar and turn it on for a few seconds, until you do not hear any sound.

6. Observe the sound and what you see in occurring in the bell jar.

7. Remove the vacuum pump hose. Record your observations.

Explanation

Prior to the use of the vacuum, we are able to hear the bell ring, because sound travels through a medium and the jar still has air, which acts as a medium. Once the air is vacuumed out, there is no longer a medium for sound to travel through, even though we still see the bell ringing, but can not hear it.

Questions

1. What factors does the speed of sound depend upon? What are some factors that it does not depend upon? It depends on the type of the material it is passing through; whether it is gas, liquid, or solid. Also how massive the atoms are, how easy or had it is to get them vibrating. It does not depend on the frequency or wavelength of the sound wave.

2. Why doesn't sound travel in a vacuum? In a vacuum there are no medium, no atoms, to carry the sound waves.

3. Why would it be pointless to attempt to detect sounds from other planets, even with the best audio detectors? Sound cannot travel through empty space.

Everyday examples of the principles illustrated

Photos

References

Sound Activities

Physics Classroom

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