Sound Waves

Introduction
Sound waves are all around us. They come from different sources. What are some of these sources? Did you know that sounds also influence your feelings and reactions? For instance how would you respond to a sound from a barking dog or guitar as shown in Figure 5.1 ?

This chapter, will enable you to describe the nature of sound waves, understand
the fact that they are produced by vibrating bodies, and how to determine the
velocity of sound waves using the echo method.

5.1: Nature of Sound Waves

5.1.1: Production of Sound Waves
When a time keeper at school rings the bell, sound is produced. How does
the bell produce the sound? Why is it that when the bell is not hit, it does not
produce the sound?
Activity 5.1 Investigating how different objects produce sound
Key question: Describe how sound is produced by objects.
What you need: desk, tuning forks, water, whistle, speaker from an old radio,
cells, ICT resources.
Initial question: What is sound?
What to do (In groups):

1. Let one person sing or talk and you touch his/her neck gently.
2. Choose another person and let him blow a whistle.
3. Connect the speaker to the cells using wires as you touch their surfaces and make observations.
4. Hit the desk and tuning forks to produce sound as you touch their surfaces and note your observations.

5. How is sound produced by;
   (b) whistle? (c) speaker? (d) tuning fork? (e) desk?
   (a) your friend?
6. Basing on your observations in part (3) and (4), explain how sound is produced.
7. Suggest any other objects which produce sound.
8. State any three applications of sound waves.
   5.1.2: Properties of Sound Waves
   You might have noticed that different objects produce different sounds. For instance, what distinguishes the sound produced by a trumpet from that produced by a drum?

Activity 5.2 Investigating the properties of sound waves
Key question: Explain the properties of sound.
What you need: Whistle, drum, sticks and a radio.
Initial question: What is loudness of sound?
What to do (In groups):

1. Let one person of the group use the sticks to hit the drum first gently and afterwards very hard. Note down your observations.
2. Let another person blow the whistle hardly. State any observations made.
3. Switch on the radio, gradually increase and decrease the volume as you note down your observations.
4. Make research about the properties of sound.
   Conclusion and Application
5. How are the two sounds produced in step (1) above different from one another and why?
6. How is the sound from the whistle different from that of the drum?
7. What do you understand by pitch?
8. Which properties of sound determine its;
   c) timbre
   a) loudness
   b) pitch
9. When is sound considered to be noise?
   10.What are some of the effects of noise in the environment? How can noise be minimised?

Compare the sounds shown in Figure 5.2. Which of the sounds;
is louder?
has the highest pitch? (b)
(a)
5.1.3: Transmission of Sound waves
You are aware that there are many heavenly objects which exist in space. Why do you think we do not hear the sound they produce during their movements?
Activity 5.3 | Investigating the transmission of sound energy Key question: Explain how sound is transmitted?

What you need: relevant text books, Bell jar, vacuum pump, electric bell, cork, switch
Initial question: what is meant by the term material medium?
What to do (In groups):

1. Place an electric bell inside a bell jar as shown in Figure 5.3.

2. Connect the bell to the power source.
3. Gradually pump the air outside the bell jar using a vacuum pump and note the observations.

4.What name is given to the region created inside the jar when all the air
was pumped out?
5.What happened to the sound as the air was gradually pumped out? Explain.
6.Basing on your observations, what does sound require to travel?
7.Explain how sound is transmitted through materials.
8.How does density and arrangement of particles in a medium affect the speed of sound?
5.2: Velocity of Sound in Air
Just like light, sound travels at a specific speeds through different materials.
How can you measure the speed of sound? Did you know that there are objects
which travel faster than sound?

Activity 5.4 Determining the velocity of sound in air Key question: How can you determine the velocity of sound in air.
What you need: ICT resource, relevant textbooks, pieces of wood, tall wall, stop clock, tape measure.
Initial question: Define an echo
What to do (In groups):

1. Let two people, one with a stop clock and the other with wooden pieces
   stand at distance of at least 50 m from the wall.
2. IJse the pieces of wood to produce echoes and the stop clock to time them.
   Conclusion and Application
3. What is the distance travelled by the sound to and from the wall?
4. Determine the velocity at which the sound travels in air.
5. State and explain the factors you think will affect the velocity of sound.
6. Suggest applications of the echoes in daily life.

1.Peter stands in front of a cliff and makes a loud sound. He hears the echo after 1.9 s. Calculate the speed of sound in air if the distance between him
and the cliff is 500 m. State and explain the possible sources of errors.
2.Mariam saw a lightning bolt and she immediately started timing. She hard the thunder 3 seconds later. How far away was she from the thunderstorm?
3.A sound wave of frequency 200 Hz is produced 450 m away from a high wall. If the echo is received after 2.5 seconds. Find the wave length of sound wave.
4.A student stood from a high wall and made 50 claps in one minute. If the velocity of sound is 330 s, find the distance between the student
and the wall.
5.A student, standing between two vertical cliffs and 480 m from the nearest cliff shouted. She heard the 1st echo after 3 seconds and the
second echo 2 seconds later. Calculate;
(a) The velocity of sound in air
(b) The distance between the cliffs

Chapter 5 Summary
In this chapter, you have learnt that; Sound waves are generated by vibrating bodies.
The amplitude of these atomic vibrations define the loudness of sound Pitch of sound is a property which depends on the frequency of a sound wave.
Sound waves require a material medium for their propagation.
The speed of sound waves in a medium varies depending on the density of the medium.
The speed of sound can be determined using the echo method.