Chapter 11 Sound

The Nature of Sound General 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 Hearing The outer ear gathers sound waves, passing them through the ear canal to a tough membrane called the eardrum. The vibrating eardrum passes the sound to three tiny bones in the middle ear- hammer, anvil, and stirrup- which amplify the sound wave. 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. As the hair cells in the cochlea vibrate, nerve impulses are sent through the auditory nerve to the brain.

Hammer Anvil Stirrup Cochlea Outer Ear 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.

Low -amplitude (top) and High-amplitude (bottom) Sound Waves and High Sound

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 Ultrasonic waves are used in medical diagnosis and treatment. They also are used to estimate the size, shape, and depth of underwater objects.

Infrasonic Waves Infrasonic, or subsonic waves have frequencies below 20 Hztoo 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.