1. Chapter 21 Preview Section 1 What Is Sound?
The Nature of Sound
Preview
Section 1 What Is Sound?
Section 2 Properties of Sound
Section 3 Interactions of Sound Waves
Section 4 Sound Quality
Concept Mapping

2. Chapter 21
Section 1 What Is Sound?
Bellringer
If you have ever been near a large fireworks display, you may have felt the sound of the explosions. Think of other times when you might feel sound and describe them in your science journal.

3. Chapter 21 Objectives Describe how vibrations cause sound.
Section 1 What Is Sound?
Objectives
Describe how vibrations cause sound.
Explain how sound is transmitted through a medium.
Explain how the human ear works, and identify its parts.
Identify ways to protect your hearing.

4. Chapter 21 Sound and Vibrations
Section 1 What Is Sound?
Sound and Vibrations
All sounds are created by vibrations. A vibration is the complete back-and-forth motion of an object or material.
The next slide shows how a stereo speaker produces sound.

5. Chapter 21
Section 1 What Is Sound?

6. Sound and Vibrations, continued
Chapter 21
Section 1 What Is Sound?
Sound and Vibrations, continued
Sound Waves are longitudinal waves that are caused by vibrations, which are then carried through a substance and transfers energy.
The particles of the substance vibrate back and forth along the path that the sound waves travel.
Sound is transmitted through the vibrations and collisions of the particles.

7. Sound and Vibrations, continued
Chapter 21
Section 1 What Is Sound?
Sound and Vibrations, continued
Sound waves travel in all directions away from their source.
However, the air or other matter through which the wave is traveling does not travel with the sound waves. The particles of air only vibrate back and forth.

8. Sound and Vibrations, continued
Chapter 21
Section 1 What Is Sound?
Sound and Vibrations, continued
Sound and Media All sound waves require a medium (plural, media).
A medium is a substance through which a wave can travel by vibrating particles in the material. Air is the most common medium of sound waves.
There are no particles to vibrate in a vacuum. So, no sound can be made in a vacuum.

9. Chapter 21 How You Detect Sound
Section 1 What Is Sound?
How You Detect Sound
Your ears are divided into three regions: the outer ear, the middle ear, and the inner ear.
The outer ear collects sound waves. Then, organs in the middle ear increase the size of the sound wave’s vibrations. The inner ear changes the vibrations into electrical signals that your brain interprets as sound.

10. Chapter 21
Section 1 What Is Sound?

11. How You Detect Sound, continued
Chapter 21
Section 1 What Is Sound?
How You Detect Sound, continued
Making Sound Versus Hearing Sound Making sound is separate from hearing sound. Sound can be made and not be heard.
Suppose that a tree falls and and no one is around to hear it. When the tree falls, the tree and the ground vibrate. These vibrations create a sound wave.
So, a sound was made—it just wasn’t heard.

12. Hearing Loss and Deafness
Chapter 21
Section 1 What Is Sound?
Hearing Loss and Deafness
The parts of the ear must work together for you to hear. If any part of the ear is damaged or does not work properly, hearing loss or deafness may result.
Loud sounds can cause damage the cochlea. Damage to the cochlea or any other part of the inner ear usually results in permanent hearing loss.

13. Hearing Loss and Deafness, continued
Chapter 21
Section 1 What Is Sound?
Hearing Loss and Deafness, continued
Protecting Your Hearing There are some simple ways to protect your hearing.
For example, you can wear earplugs to block out loud sounds. You can listen at a lower volume when you are using headphones. You can also move way from sources of loud sounds.

14. Chapter 21
Section 2 Properties of Sound
Bellringer
You are the commander of a space station located about halfway between Earth and the moon. You are in the Command Center, and your chief of security tells you that sensors have just detected an explosion km from the station. How long will it be before you hear the sound of the explosion?
Write your answer in your science journal.

15. Chapter 21 Objectives Compare the speed of sound in different media.
Section 2 Properties of Sound
Objectives
Compare the speed of sound in different media.
Explain how frequency and pitch are related.
Describe the Doppler effect, and give examples.
Explain how amplitude and loudness are related.
Describe how amplitude and frequency can be “seen” on an oscilloscope.

16. Chapter 21 The Speed of Sound
Section 2 Properties of Sound
The Speed of Sound
The speed of sound depends only on the medium in which the sound is traveling.
How the Speed of Sound Can Change Sound travels quickly through air, but it travels even faster in liquids and even faster in solids.
Temperature also affects the speed of sound. The cooler the medium is, the slower the speed of sound.

17. Chapter 21 Pitch and Frequency
Section 2 Properties of Sound
Pitch and Frequency
How low or high a sound seems to be is the pitch of that sound. The pitch of a sound is related to the frequency of the sound wave.
Frequency and Hearing The frequencies of some sounds are out of the range of human hearing. Sound that have a frequency too high for people to hear are called ultrasonic.

18. Chapter 21
Section 2 Properties of Sound

19. Pitch and Frequency, continued
Chapter 21
Section 2 Properties of Sound
Pitch and Frequency, continued
The Doppler Effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound.

20. Chapter 21
Section 2 Properties of Sound

21. Doppler Effect and Sound
Chapter 21
Section 2 Properties of Sound
Doppler Effect and Sound
Click below to watch the Visual Concept.
Visual Concept

22. Loudness and Amplitude
Chapter 21
Section 2 Properties of Sound
Loudness and Amplitude
Loudness is a measure of how well a sound can be heard.
Energy and Vibration The harder you strike a drum, the louder the sound. As you strike the drum harder, you transfer more energy to the drum.
The drum moves with a larger vibration and transfers more energy to the air around it.

23. Loudness and Amplitude, continued
Chapter 21
Section 2 Properties of Sound
Loudness and Amplitude, continued
Increasing Amplitude The amplitude of a wave is the largest distance the particles in a wave vibrate from their rest positions. The larger the amplitude, the louder the sound.
Measuring Loudness The most common unit to express loudness is the decibel (dB). The softest sounds a human can hear are at a level of 0 dB.

24. “Seeing” Amplitude and Frequency
Chapter 21
Section 2 Properties of Sound
“Seeing” Amplitude and Frequency
A device called an oscilloscope can graph representations of sound waves, as shown below. Notice that the graphs look like transverse waves rather than longitudinal waves.

25. “Seeing” Amplitude and Frequency
Chapter 21
Section 2 Properties of Sound
“Seeing” Amplitude and Frequency
From Sound to Electrical Signal A microphone attached to an oscilloscope changes a sound wave into an electrical signal. The electrical signal is graphed on the screen in the form of a wave.
The graph shows the sound as if it were a transverse wave. So, the sound’s amplitude and frequency are easier to see.

26. Chapter 21
Section 3 Interactions of Sound Waves
Bellringer
Answer the following question in your science journal.
On an oscilloscope, does a wave with a larger amplitude indicate louder sound or higher pitch?
As frequency increases, does pitch get higher or lower?
What is the speed of sound dependent on?
What do think happens when two sound waves interact with each other?

27. Chapter 21
Section 3 Interactions of Sound Waves
Objectives
Explain how echoes are made, and describe their use in locating objects.
List examples of constructive and destructive interference of sound waves.
Explain what resonance is.

28. Reflections of Sound Waves
Chapter 21
Section 3 Interactions of Sound Waves
Reflections of Sound Waves
Reflection is the bouncing back of a wave after it strikes a barrier. An echo is a reflected sound wave.
The strength of a reflected sound wave depends on the reflecting surface. Sound waves reflect best off smooth, hard surfaces.

29. Reflections of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Reflections of Sound Waves, continued
The images below explain why you are more likely to hear an echo in a gymnasium than you would in an auditorium.

30. Reflections of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Reflections of Sound Waves, continued
Echolocation is the use of reflected sound waves to find objects. Animals, such as bats, use echolocation to hunt food and find objects in their path.
Animals that use echolocation can tell how far away something is based on how long it takes sound waves to echo back to their ears.

31. Chapter 21
Section 3 Interactions of Sound Waves

32. Reflections of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Reflections of Sound Waves, continued
Echolocation Technology People use echoes to locate objects underwater by using sonar. Sonar is a type of electronic echolocation.
Sonar can also help navigators on ships avoid icebergs and can help oceanographers map the ocean floor.

33. Chapter 21
Section 3 Interactions of Sound Waves

34. Reflections of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Reflections of Sound Waves, continued
Ultrasonography is a medical procedure that uses echoes to “see” inside a patient’s body without doing surgery.
Ultrasonography is used to examine kidneys, gallbladders, and other organs. It is also used to check the development of an unborn baby in a mother’s body.

35. Interference of Sound Waves
Chapter 21
Section 3 Interactions of Sound Waves
Interference of Sound Waves
Interference happens when two or more waves overlap. Two types of interference are shown below.

36. Interference of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Interference of Sound Waves, continued
Interference and the Sound Barrier As the source of a sound—such as a jet plane—gets close to the speed of sound, the sound waves in front of it combine by constructive interference.
The result of this interference is a high-density compression called the sound barrier.

37. Interference of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Interference of Sound Waves, continued
When a jet reaches speeds faster than the speed of sound, the sound waves trail off behind the jet. At their outer edges, the sound waves combine by constructive interference to form a shock wave.
A sonic boom is the explosive sound hear when a shock wave reaches your ears.

38. Chapter 21 Sonic Boom Click below to watch the Visual Concept.
Section 3 Interactions of Sound Waves
Sonic Boom
Click below to watch the Visual Concept.
Visual Concept

39. Interference of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Interference of Sound Waves, continued
Interference and Standing Waves A pattern of vibration that looks like a wave that is standing still is called a standing wave.
Standing waves form because of interference. Where you see maximum amplitude, waves are interfering constructively. Where the wave seems to be standing still, waves are interfering destructively.

40. Interference of Sound Waves, continued
Chapter 21
Section 3 Interactions of Sound Waves
Interference of Sound Waves, continued
The frequencies as which standing waves are made are called resonant frequencies.
The lowest resonant frequency is called the fundamental. Higher resonant frequencies are called overtones.

41. Chapter 21
Section 3 Interactions of Sound Waves
Resonance
Resonance happens when an object vibrating at or near a resonant frequency of a second object cause the second object to vibrate.
Resonance in Musical Instruments Musical instruments use resonance to make sound. Vibrations are amplified when resonance causes standing waves to form inside instruments.

42. Chapter 21
Section 4 Sound Quality
Bellringer
Answer the following questions in your science journal.
Which strings on a piano have lower pitch?
Why does a tuba have a lower pitch than a trumpet?
Why are some sounds pleasing to hear and some sounds not? Explain your answer.

43. Chapter 21
Section 4 Sound Quality
Objectives
Explain why different instruments have different sound qualities.
Describe how each family of musical instruments produces sound.
Explain how noise is different from music.

44. Chapter 21 What Is Sound Quality?
Section 4 Sound Quality
What Is Sound Quality?
Imagine that the same note is played on a piano and on a violin. You could probably tell the instruments apart because they make different sounds.
The notes sound different because a single note on an instrument actually comes form several different pitches: the fundamental and several overtones, as shown at right.

45. What Is Sound Quality?, continued
Chapter 21
Section 4 Sound Quality
What Is Sound Quality?, continued
The result of several pitches mixing together through interference is sound quality.
Instruments sound different because each has a unique sound quality, as shown below.

46. Sound Quality of Instruments
Chapter 21
Section 4 Sound Quality
Sound Quality of Instruments
The difference in sound quality among different instruments come from their structural differences.
All instruments produce sound by vibrating. But instruments vary in the part that vibrates and the way the vibrations are made.
Three families of instruments are string instruments, wind instruments, and percussion instruments.

47. Sound Quality of Instruments, continued
Chapter 21
Section 4 Sound Quality
Sound Quality of Instruments, continued
String Instruments Violins, guitars, and banjos are examples of string instruments. String instruments make sound when their strings vibrate after being plucked or bowed.
The pitch of a string can be changed by changing the string’s length. Shorter strings vibrate at higher frequencies, and thus have higher pitches.

48. Sound Quality of Instruments, continued
Chapter 21
Section 4 Sound Quality
Sound Quality of Instruments, continued
Wind Instruments Saxophones, flutes, French horns, and tubas are examples of wind instruments. Wind instruments make sound when a vibration is created at one end of its air column.
Pitch is changed by changing the length of the air column. The longer the air column is, the lower the pitch is.

49. Sound Quality of Instruments, continued
Chapter 21
Section 4 Sound Quality
Sound Quality of Instruments, continued
Percussion Instruments Drums, bells, and cymbals are examples of percussion instruments. Percussion instruments make sound when struck.
Instruments of different sizes are used to get different pitches. Usually, the larger the instrument is, the lower the pitch is.

50. Chapter 21
Section 4 Sound Quality
Music or Noise?
Most of the sounds you hear are noises. Noise is any sound that is of a random mix of frequencies.
The difference between a musical sound and noise is shown in the images below.

51. Chapter 21 Concept Mapping
The Nature of Sound
Concept Mapping
Use the terms below to complete the Concept Mapping on the next slide.
loudness
oscilloscope
frequency
sound
interference
pitch
medium

52. Chapter 21
The Nature of Sound

53. Chapter 21
The Nature of Sound