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Project Summary

Difficulty	3
Time required	Very Short (a day or less)
Prerequisites	Basic understanding of how sound travels
Material Availability	Readily available
Cost	Low ($20 - $50)
Safety	Minor injury possible. Adult supervision required when using heat source.

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Abstract

Objective

The goal of this project is to investigate how decreasing the amount of air in a container affects the container's ability to transmit sound.

Introduction

"Could I get some peace and quiet around here?" We have all longed for a moment of silence. But even if our brother stops talking and our baby sister stops crying, we would still be able hear the traffic on the freeway or the neighbor's dog barking. What causes these sounds? Will we ever be able to get some peace and quiet?

Sound is produced by vibrations from material objects. These vibrations move in waves that travel through gases (like air), liquids (like water), and solids (like the ground).

Our ears hear sound when these waves reach our eardrums. The sound waves then cause the bones in our middle ear vibrate and the vibrations are transmitted to fluid in our inner ear. Then the vibrations travel to the inner ear hair cells and to the nerves that carry the signal to our brains.

Scientists describe different sound waves by their amplitude (how loud the sound is) and frequency (the pitch of the sound). Complex sounds, like human speech, contain energy at many different frequencies at the same time.

In this experiment, you will show that in order to be heard, sound must have a medium to travel through.

Terms, Concepts and Questions to Start Background Research

• sound
• waves
• vibrations

Questions

• How do our ears hear sound?
• What makes sounds louder or softer?
• What makes sounds high pitched or low pitched?

Bibliography

• Introduction to General Physics Concepts:
  Hewitt, Paul G. 2002. "Conceptual Physics," Prentice Hall, IL.
• Simple Physics Concepts for Kids:
  Keller, R.W. 2005. "Real Science for Kids: Physics, Level 1," Gravitas Publications, Inc., NM.
• Website on How Sound Travels Through Water:
  An Ocean of Sound
  http://oceanlink.island.net/oinfo/acoustics/acoustics.html

Materials and Equipment

• iron wire
• wire cutters
• small bell
• 250 ml (or larger) flat-bottom (Ehrlenmeyer) flask, made of borosilicate glass (won't shatter when subjected to rapid changes in temperature)
• rubber stopper to fit flask tightly
• water
• heat source (Bunsen burner or alcohol lamp)
• timer
• hot mitt

Experimental Procedure

1. Cut the wire to a length of about 8–10 cm.
2. Attach the bell to one end of the wire and poke the other end firmly into the rubber stopper.
3. Place the stopper in the flask. The bell should be hanging freely in the middle of the flask.
4. Gently shake the flask from side-to-side to ring the bell. Record your observations in your lab notebook.
5. Remove the stopper from the flask and add water to the flask to a depth of about 0.5 cm.
6. With the flask open (i.e., with the stopper and bell still off the flask), place the flask on the heat source and bring the water to a boil. Boil for one timed minute. Do not allow the flask to boil dry.
7. With the hot mitt, carefully remove the flask from the heat source.
8. Quickly place the stopper, wire, and bell back into the flask. Caution! The glass will be hot! Take care not to touch the flask as you replace the stopper. Note the time in your lab notebook.
9. At regular intervals (try every 3–5 min), gently shake the flask from side-to-side to ring the bell. Record your observations in your lab notebook. Keep your eyes and ears open and write down what you see and hear. Here are some suggestions:
   1. Be sure to note the time of each observation.
   2. Note the condition of the inside of the flask. For example, is the air inside the flask clear? Do you see condensation on the sides of the flask?
   3. Note your observations of the sound. Can you hear the bell?
   4. When the flask has cooled to room temperature, the trial is complete.
   5. Keep observing as you prepare the next trial. For example, is it harder to remove the stopper now than when you first put it in?
10. For any experiment, it is important to do multiple trials to assure that your results are consistent.
    1. Repeat the experiment at least two more times, and record the results of each trial.
    2. Add more water to the flask, if needed.
11. Summarize your results. You could make a graph that shows how the sound changes over time after the flask is sealed. You could also graph how the appearance of the air inside the flask changes over time.

Variations

• Can you think of a way to measure the loudness of the bell with more accuracy?
• What happens if you put the flask into an ice bucket (use crushed ice) after replacing the stopper and bell? Caution: as noted in the Materials and Equipment section, be sure that your flask is made of borosilicate glass, which will not shatter when subjected to rapid changes in temperature .
• Compare the sound a bell makes in air vs. water.

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

La Né Powers

Last edit date: 2006-02-22 00:54:39

Career Focus

If you like this project, you might enjoy exploring careers in Physics.

Physicist Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy.

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