University of Virginia
Physics Department

The Energy of Sound

A Physical Science Activity

2003 Virginia SOLs

 

Objectives

Students will

 

Motivation for Learning

Demonstration

Materials

 

Procedure

  1. Hold the pipe vertically in the middle with one hand and tap the top end with the flat palm firmly, holding it against the tube. Ask students to listen carefully for the tone that is produced.
  2. Tap the end of the pipe again with the flat of your hand, but this time release your hand immediately after contact with the tube. A different tone will be produced.
  3. Keep alternating the kinds of taps so that the students can distinguish between the tones.
  4. Ask the students to identify which kind of tap produced the highest pitch sound and why different types of tapping produce different tones.

In this demonstration, tapping on the top of the pipe produces a vibrating air column inside the pipe. If you keep the palm of your hand firmly against the opening, a long wave is generated. The tone produced is low. When you move your hand away from the opening quickly after tapping, a short wave is generated producing a higher tone. The students should recognize that it is the vibrating column of air inside the pipe making the sound.

 

Background Information

The purpose of these activities is to show students that sound is produced by vibrating objects and that the sound can be transmitted through various mediums. The characteristics of the medium also determine the ease at which the sound can travel through them. The students should see that the denser materials tend to be the best transmitters of sound. Sound travels in longitudinal waves with a series of compressions and rarefactions. The closer the particles of the medium, the easier the sound energy can move through it.

Students should also see that the length of a vibrating material determines the pitch of the sound produced by that material. In the laboratory below (part 3), a higher pitch sound came from the rubber band when its length was decreased. The short rubber band vibrated faster than the longer one and produced a higher frequency pitch.

In part 3 of the lab below, the sound produced by tapping the soda bottles arises from the glass and water vibrating together. The more water in the bottles, the longer the vibrating materials and the lower the pitch of the sound. When you blow over the top of the bottle, the column of air over the water is vibrating, not the glass or water, as a result, the more water in the bottle the shorter the column of air and the higher the pitch.

  

Student Activity

To print out the Student Copy only, click here.

  PART 1

What type of matter causes sound, what type of material can carry the sound, and what factors influence the pitch of the sound?

Materials

  • 20 cm of thread
  • Rubber mallet
  • Ring stand
  • Tuning fork
  • Thumbtack
  • Cork (or puffed cereal or "peanut" insulation pieces)
  • Paper
  • Scissors

Procedure

Follow the directions on the Data Sheet and record observations.

 

Data Sheet

To print out the Data Sheet only, click here.

1. Keeping your mouth tightly closed, hum a long note. Place your hands on the sides of your throat and describe what you feel.

 

2. Hold your mouth as if you are going to whistle. Again, hum a long note and describe the feeling of your lips.

 

3. Attach one end of the thread to the ring stand. Using the tack, attach the cork (or puffed cereal or "peanut" insulation) to the other end of the thread. Strike the tuning fork with the mallet and bring it very close to the cork but do not touch the cork. What happens to the cork?

cork

4. Cut a piece of paper 2 ½ inches long and ½ inches wide. Hold the paper between your thumbs and blow on it . Record your observations.

 

5. From your observations in the last activities, make a general statement about the type of motion that causes sound.

 

PART 2

Which materials transmit sound the best?

Materials

 

Procedure

As you conduct your experiments record your observations in your own words in the table below.

  1. Hold a ticking clock as far away from your body as you can. Record whether or not you can hear the ticking in the table.
  2. Press one end of the wooden dowels against the back of the clock and the other end against the little flap that is beside your ear. Enter your results in the table.
  3. Repeat step #2 using a metal rod instead of the wooden dowel. Record your observations in the table.
  4. Tie the handle of the spoon to the center of the meter long string. Hold the string at each end and knock the spoon against the table to make it ring. Listen to the ringing sound for a few seconds then press the ends of the strings against your ears. Observe and record the difference in sound with and without the string pressed against your ear.
  5. This time knock the spoon against the table. When you can no longer hear the sound of the ringing spoon, press the ends of the string against your ears. Record whether or not you could hear the ringing of the spoon again.

 

Data Sheet

To print out the Data Sheet only, click here.

 

Sources of Sound

Sound Carrier

Description of Sound

Clock

Air

 

 

Clock

Wood

 

 

Clock

Metal

 

 

Vibrating Spoon

Air

 

 

Vibrating Spoon After 5 sec.

String

 

 

Vibrating Spoon (quiet)

String

 

 

 

Questions:

1. Could you hear the watch ticking when you held it at arm's length?

 

2. Could you hear the watch ticking when you held it against the wooden dowel?

 

3. Could you hear the watch ticking when you held it against the metal rod?

 

4. Based on what you heard, which is the best carrier of sound- air, metal, or wood? Which is the second best?

1st _________________________ 2nd ________________________

 

5. How did the sound of the spoon change when the string was held against your ears?

 

6. When the ringing of the spoon was too quiet to be heard through the air, could it be heard through the string?

 

7. Is the string a better carrier of sound than air is?

 

PART 3

What determines the pitch of sound?

Materials

 

Procedure

Follow the directions on the Data Sheet and record observations.

 

Data Sheet

To print out the Data Sheet only, click here.

1. Press a ruler tightly against the desk or table. Allow most of the ruler to hang over the edge. Pull down on the ruler with the other hand, release it and make it vibrate. Listen to the sound made by the vibrating ruler.

 

2. Slide a little more of the ruler onto the desk or table. Press the ruler on the desk and with your other hand make it vibrate again. Listen to the pitch of the sound. How does it compare to the pitch in number one?

 

3. Keep sliding a little more of the ruler onto the table or desk to shorten the length of the vibrating portion. Each time you shorten the length record the pitch of the sound in the table. What happens to the pitch of the sound as you shorten the length of the vibrating portion of the ruler?

 

 

4. Stretch the rubber band over the length of a textbook and place two wooden dowels or pencils underneath the rubber band at each end of the book. Gently pluck the rubber band and listen for the pitch of the sound.

book

 

5. Move the pencils closer together and pluck the rubber band again between the two pencils. Keep moving the pencils closer and plucking the rubber band in between them each time. What happens to the pitch of the rubber band as the pencils get closer together?

 

 

6. Place two more rubber bands of different thickness around the pencils and book. Pluck each individually and determine the relationship between the thickness of the rubber band and the pitch. Write your results below.

 

 

7. Fill one 12 oz soda bottle 1/3 full with water. Fill a second 12 oz bottle ½ full and a third ¾ full. Tap on each bottle with a pencil and compare the pitch of the sound coming from each one. List the bottles from highest to lowest pitch. Use water levels inside to designate the different bottles.

Highest pitch ___________________________________

Middle pitch ___________________________________

Lowest pitch ____________________________________

 

 

8. In the bottles of water, what is vibrating and making the sound?

 

 

9. Use the three 12 oz bottles again, but this time instead of tapping the bottles blow over the tops and try to produce a sound in each one. List the bottles from highest to lowest pitch.

Highest pitch _______________________

Medium pitch _______________________

Lowest pitch _______________________

 

10. What is vibrating to produce the sound, when you blow over the top of the bottle?

 

 

Extensions

Ask the students to use more soda bottles. Fill each one with a different amount of water, and by either blowing over or by taping the sides of the bottles, play a simple song. They can perform their songs in front of the class.

 

Students with Special Needs

Some students may have difficulty manipulating some of the materials (especially the rubber bands around the book). These students can work with partners or in small groups.

Click here for further information on laboratories with students with special needs.

 

Assessment

1. What type of motion produces sound?

 

2. How does the density of a material affect its ability to carry sound?

 

3. State the relationship between the thickness of a vibrating object and its pitch.

 

4. State the relationship between the length of a vibrating object and its pitch.