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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

Chapter 21

Concept Mapping



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.

Chapter 21



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.

Chapter 21



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.

Chapter 21


Section 1 What Is Sound?Chapter 21



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.

Chapter 21



• 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.

Chapter 21 Section 1 What Is Sound?




• 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.

Chapter 21



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.

Chapter 21


Section 1 What Is Sound?Chapter 21



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.

Chapter 21



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.

Chapter 21



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.

Chapter 21



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 61.054 km from the station. How long will it be before you hear the sound of the explosion?

Write your answer in your science journal.

Chapter 21



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.

Chapter 21



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.

Chapter 21



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.

Chapter 21


Section 2 Properties of SoundChapter 21



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.

Chapter 21





Doppler Effect and Sound

Click below to watch the Visual Concept.

Visual Concept



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.

Chapter 21



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.

Chapter 21



“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.

Chapter 21



“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.

Chapter 21


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?

Section 3 Interactions of Sound WavesChapter 21


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.



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.



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.




• 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.






• 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.






• 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.



Interference of Sound Waves

• Interference happens when two or more waves overlap. Two types of interference are shown below.



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.




• 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.



Sonic Boom

Click below to watch the Visual Concept.

Visual Concept




• 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.




• 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.



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.




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.

Chapter 21



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.

Chapter 21


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.

Chapter 21 Section 4 Sound Quality

• 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.


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.



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.



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.




• 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.




• 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.



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.



Use the terms below to complete the Concept Mapping on the next slide.

Concept Mapping

loudnessoscilloscopefrequencysound

interferencepitchmedium

The Nature of SoundChapter 21





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< BackNext >PreviewMain The Nature of Sound Preview Section 1 What Is Sound?What Is Sound? Section 2 Properties of SoundProperties of Sound Section 3 Interactions