Speaking Under Water

Research Questions:

• How far away can a swimmer be and still hear what you are saying?
• How does your voice change under water? Does it sound higher or lower?

Scientists use sonar to detect sound under water in order to map out the ocean floor, find fish, and detect enemy submarines. Sound waves are sent out. Scientists then wait for an echo. This echo means that the sound has hit something. Scientists determine the location of the object hit by measuring the speed with which the echo returns.

Materials:

• 1 Empty tennis ball can
• A volunteer
• A swimming pool
• Pen or pencil
• Lab notebook

Experimental Procedure:

1. Hold an upright tennis ball can so that most of it is under water, but water is not able to get inside of it.
2. Put your mouth close to it, and practice speaking into it.
3. Ask your volunteer to get into the water, go under the water, and listen while you speak into the can. Could your volunteer hear you? How did your voice sound? Record your observations.
4. Repeat the above steps several more times, asking your volunteer to move farther and farther away each time you speak. Record your observations each time.
5. Analyze your data. How did your voice sound? Did it get higher or lower? Did it change the farther away your volunteer was? How far could your volunteer go and still understand what you were saying?

Terms/Concepts: sound; sonar; echo

References: More Than 100 Experiments For Science Fairs and Projects, by Vicki Cobb (Scholastic, 2001).