Good Vibrations-Tuning Fork by Anna Mkrtchyan

Author

Anna Mkrtchyan, AGBU Manoogian-Demirdjian School

Principles

Sound waves-Mechanical Waves

Standards

Materials needed

• eraser, rubber

• plastic cup of water, small

• tuning fork

Procedure

1. Gently strike a tuning fork on a rubber eraser. Watch the prongs, and listen for a sound. Describe what you see and hear.

2. Lightly touch the fork with your fingers. What do you feel?

3. Grasp the prongs of the fork firmly with your hand. What happens to the sound?

4. Strike the tuning fork on the eraser again, and dip the prongs in a cup of water. Describe what happens to the water.

5. Record your observations.

Explanation

A tuning fork serves as a useful illustration of how a vibrating object can produce sound. The fork consists of a handle and two tines. When the tuning fork is hit with an eraser, the tines begin to vibrate. The back and forth vibration of the tines produce disturbances of surrounding air molecules. As a tine stretches outward from its usual position, it compresses surrounding air molecules into a small region of space; this creates a high pressure region next to the tine. As the tine then moves inward from its usual position, air surrounding the tine expands; this produces a low pressure region next to the tine. The high pressure regions are known as compressions and the low pressure regions are known as rarefactions. As the tines continue to vibrate, an alternating pattern of high and low pressure regions are created. These regions are transported through the surrounding air, carrying the sound signal from one location to another.

Questions

• 1. How do your observations demonstrate that sound waves are carried through vibrations? The water begins to move when the tuning fork is placed in the water. Vibrations from the tuning fork caused the water's movement.

  2. Particularly loud thunder can cause the windows of your room to rattle. How is this evidence that sound waves carry energy? It takes energy to move the windows to cause them to rattle. Therefore, energy from the thunder's sound waves must be transferred through the air to the windows.

  3. Will the tuning fork make a different sound when you swing it than when you hold it? If yes, explain why. Yes; As the tuning fork swings toward the listeners, the pitch is higher because the sound waves is front of it are closer together and therefore gave a higher frequency. As the tuning fork swings away from the listeners, the pitch is lower because the sound waves are farther apart and therefore have a lower frequency.

Everyday examples of the principles illustrated

Sound waves are produced by vibrating objects. Whether it be the sound of a person's voice, the sound of a piano, the sound of a trombone or the sound of a physics book slamming to the floor, the source of the sound is always a vibrating object.

Tuning forks were originally used to tune musical instruments because they emanate perfect sine wave sound patterns that allow you to fine-tune instruments to the proper pitch.

When you strike a tuning fork however, you'll notice how it causes the air around the fork to vibrate, sending out very strong vibrating impulses through the air. Because of this, they have been adopted by healers who use them to increase the amount of energy on parts of the body they are trying to heal.

Photos

Movies

References

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Longitudinal Waves and Tuning Forks

Physical Science textbook