Sound and Water: Tuning Forks and Water

Sounds are vibrations that move through matter. When a tuning fork is struck with a rubber mallet, you cannot see the sound waves move out from the tuning fork, but you can hear them. When the mallet strikes the tuning fork, air molecules quickly bounce off the fork. The vibrations move through the air until they reach your ear, causing it to hear a sound. The vibration of air molecules is invisible to us. However, we can witness this vibration if it occurs in a denser medium such as water. In this activity you will observe the pattern of vibrations that occurs when a tuning fork is set in motion.

Materials

Tuning fork; Glass of water; Rubber mallet; Paper towels

Activity

1. Place the glass of water on the paper towels.
2. Strike the tuning fork with the rubber mallet and look closely at the motion of the tuning fork. Can you see any movement of air molecules? Bring the tuning fork close to your ear and listen for the sound produced.
3. Stop the motion of the tuning fork with your hand.
4. Strike the tuning fork again and lower the upper part of the fork several inches into the water. What happens to the water?

Follow-Up Questions

1. Could you see any motion of air molecules the first time you struck the tuning fork and held it in the air?
2. What happened when you struck the tuning fork the second time and lowered it into the glass of water?
3. How can you relate what you saw in the water to what happens when sound is produced in the air?

Answers

1. No.
2. Tiny water waves were created.
3. Vibrations produced in water are visible and mimic the invisible vibrations of air molecules.

Extension

Try variations of this activity by striking the tuning fork and holding it just above the surface of the water. What happens to the water? Also strike two tuning forks and place them both in the water at the same time. What happens?