Chapter 11 Sound

The Nature of SoundGeneral Information- Review

• A wave is a repeating disturbance or movement that transfers energy through it.– Waves differ in how much energy they carry, how

fast they travel, and how they look.– Mechanical waves are waves that can only travel

through matter.

Sound Waves

• All sounds are caused by something that vibrates.

• Sound waves - formed when a vibrating object collides with air molecules, transferring energy to them.

Compressional Waves

• Have:– Compressions- dense regions (squished together)– Rarefactions- less dense regions

Medium

• A medium is the type of matter, whether liquid, solid, or gas; that sound waves travel through.– A sound wave’s speed depends on the substance of the

medium and whether the medium is solid, liquid, or gas.– Sound travels more quickly through solids and liquids

because the individual molecules are closer together than the molecules in gas.

– As a medium’s temperature increases, its molecules move faster and it conducts sound waves faster.

The 4 Stages of Human Hearing1. The outer ear gathers sound waves, passing them

through the ear canal to a tough membrane called the eardrum.

2. The vibrating eardrum passes the sound to three tiny bones in the middle ear- hammer, anvil, and stirrup- which amplify the sound wave.

3. The stirrup vibrates and transfers the sound to a membrane in the oval window, then on to the inner ear’s cochlea, a spiral-shaped structure that contains hair cells.

4. As the hair cells in the cochlea vibrate, nerve impulses are sent through the auditory nerve to the brain.

Outer Ear

Hammer AnvilStirrup

Cochlea

Eardrum

The Properties of Sound

The amount of energy a wave carries corresponds to its amplitude, which is related to the density

of the particles in the compressions and rarefactions.

and High SoundLow -amplitude (top) and High-amplitude

(bottom) Sound Waves

Intensity

Intensity is the amount of energy that flows through a certain area in a specific amount of time.– Intensity depends on sound wave’s amplitude-

whisper = low intensity and shout = high intensity– Intensity depends on the distance from the source

of sound- decreases with increasing distance

Loudness

Loudness is the human perception of sound intensity.• As the intensity of a sound wave increases, the

loudness of the sound you hear increases.• The intensity of sound can be described using a

measurement scale.• Each unit on the scale for sound intensity is called

a decibel (dB).

A Scale for Loudness On this scale, the faintest sound that

most people can hear is 0 dB. Sounds with intensity levels above 120

dB may cause pain and permanent hearing loss.

Pitch

• Pitch is how low or high a sound seems to be; it depends on frequency• High-pitched sounds correspond to high

frequencies• Low-pitched sounds correspond to low

frequencies

Frequency

• Frequency is the number of compressions or rarefactions of a sound wave that pass per second; – human ears can hear frequencies from about 20

to 20,000 Hz

Ultrasonic and Infrasonic Waves

Most people can’t hear sound frequencies above 20,000 Hz, which are called ultrasonic waves.

Even though humans can’t hear ultrasonic waves, they use them for many things.

Ultrasonic Waves

They also are used to estimate the size, shape, and depth of underwater objects.

Ultrasonic waves are used in medical diagnosis and

treatment.

Infrasonic Waves Infrasonic, or

subsonic waves have frequencies below 20 Hztoo low for most people to hear.

Infrasonic Waves

These waves are produced by sources that vibrate slowly, such as wind, heavy machinery, and earthquakes.

Infrasonic Waves

Although you can’t hear infrasonic waves, you may feel them as a rumble inside your body.

Doppler Effect

• Doppler effect is a change in pitch or frequency caused by motion of the sound source, motion of the listener, or both

Doppler Effect

• As a source of sound approaches, an observer hears a higher pitch because the sound waves are pushed closer together

• When the sound source moves away, the observer hears a lower pitch because the sound waves are more spread out

• The faster the change in position, the greater the change in frequency and pitch.

Using the Doppler Effect

The Doppler effect also occurs for other waves besides sound waves.

For example, the frequency of electromagnetic waves, such as radar waves, changes if an observer and wave source are moving relative to each other.

Using the Doppler Effect Radar guns use the Doppler effect to

measure the speed of cars.

Weather radar also uses the Doppler shift to show the movement of winds in storms, such as a tornado.

Music

• Music is composed of sounds that are deliberately used in a regular pattern.– Natural frequency is the frequency at which a

material vibrates.– Resonance is the ability of a medium to vibrate by

absorbing energy at its own natural frequency.

Music

• Sound quality- the difference among sounds of the same pitch and loudness– Fundamental frequency- the main tone played

and heard.– Overtone- vibration with a frequency that is

multiple of the fundamental frequency

Music

• Musical instruments- devices used to make musical sounds.– Strings- instruments in which sound is produced by plucking,

striking, or drawing a bow across tightly stretched strings.– Brass & woodwinds- air vibration in a resonator, or hollow

chamber that amplifies sound, with the pitch determined by the length of the vibrating tube of air.

– Percussion instruments produce sound by being struck, shaken, rubbed, or brushed.

• Beats- a pulsing vibration in loudness.

Using Sound

• Uses of sound- entertainment, warning signals, information

• Acoustics- study of sound, which can prevent excessive reverberation and create good listening environments.

Using Sound

• Echolocation- process of locating objects by sending out sound and interpreting the waves reflected back.

Using Sound

• Sonar- a system that uses the reflection of underwater sound waves to locate objects.

Ultrasound

• Ultrasound waves are used in medicine to diagnose, monitor, and treat many conditions.– Can produce images of internal structures for

detection of medical problems– Can treat certain medical problems such as kidney

stones or gallstones.