Section 1 The Nature of Sound Chapter 11 Sound Section 1 The Nature of Sound

What causes sound? Every sound is produced by an object that vibrates Example: Your voice Your vocal cords make a vibration

Sound Waves These are compressional waves Remember, in these types of waves there are both compressions and rarefactions Figure 1 p. 322

The Speed of Sound Sound waves can travel through a solid, liquid, or a gas Sound waves cannot travel through empty space For example: This is why on the Moon, astronauts must talk to each other via electronic communication equipment.

The Speed of Sound Sound waves cannot travel through empty space For example: This is why on the Moon, astronauts must talk to each other via electronic communication equipment.

The Speed of Sound Air: 347 m/s Water: 1,498 m/s Aluminum: 4,877 m/s Which do they travel through the fastest?

The Speed of Sound Sound travels the fastest in solids b/c the particles are so close together.

Human Hearing Your ears and brain work together to make sense of the different sound waves. Involves four stages

How you hear: Step 1: Ear gathers the compressional waves

How you hear: Step 2: The ear amplifies the waves

How you hear: Step 3: The waves are converted to nerve impulses that travel to the brain

How you hear: Step 4: The brain decodes and interprets the nerve impulses

Human Ear Three sections: Outer ear, middle ear, and inner ear

Outer Ear Visible part of ear, ear canal, and eardrum Visible part of ear: shaped to help catch sound waves

Outer Ear Ear canal: 2-3 cm long; size of index finger; sound waves travel through here to eardrum Eardrum: tough membrane; 0.1 mm thick When sound waves hit the eardrum they cause it to vibrate.

Outer Ear Eardrum: tough membrane; 0.1 mm thick When sound waves hit the eardrum they cause it to vibrate.

Middle Ear What are the three tiny bones in your middle ear?

Middle Ear What are the three tiny bones in your middle ear? Stirrup Anvil Hammer

Middle Ear These make a system that multiplies the force and pressure on a sound wave This causes the sound wave to amplify and causes the “oval window” to vibrate.

Inner Ear Contains the cochlea: spiral-shaped structure that contains liquid and tiny hair cells The hair cells in the cochlea begin to vibrate and send nerve impulses through the auditory nerve to the brain.

Hear loss When the tiny hair cells are damaged or destroyed your hearing will become damaged. New research suggests that these hair cells may be able to repair themselves.

Section 2 Properties of Sound Chapter 12 Sound Section 2 Properties of Sound

Amplitude in Compressional Waves Related to density of compressions and rarefactions

Low Amplitude Sound Waves The particles are less compressed in a compression The particles are less spread out in a rarefaction

High Amplitude Sound Waves Particles are more compressed in a compression Particles are more spread out in a rarefaction

Loud and Quiet Sounds Loud sound waves carry more energy than quiet sound waves

Intensity The amount of energy that passes through a certain area in a certain time

Intensity When you turn down the volume on your radio the amount of energy is , meaning the intensity is also

Intensity Determines how far away a sound can be heard

Intensity Low intensity = short distance High intensity = long distance

Losing Intensity Farther a wave travels the less intense it becomes Loses energy *Think of a basketball after you drop it

Loudness Human perception of intensity

Loudness and Intensity Loud sounds have a high intensity Quiet sounds have a low intensity

Loudness and Intensity High intensity waves cause your eardrum to move back and forth farther Also causes increased movement of the hair cells in inner ear Result: You hear a loud sound!

How Loud is too Loud?? People have different loudness perceptions

Decibel Scale Unit for measuring sound intensity dB *p. 329 Faintest Sound = 0 dB (Whisper) Pain Threshold = 120 dB (Rock Concerts)

Decibel Scale Faintest Sound = 0 dB (Whisper) Pain Threshold = 120 dB (Rock Concerts)

Pitch How high or low a sound seems Related to the frequency of a wave

Pitch & Frequency High Frequency = fast vibrations = high pitch Low Frequency = slow vibrations = low pitch

Ultrasonic Waves Sound frequencies above 20,000 Hz are ultrasonic Humans can hear waves from frequency of 20 Hz- 20,000 Hz

Ultrasonic Waves Used in medical diagnosis and treatment Used to locate underwater objects Dogs can hear up to 35,000 Hz Bats can hear higher than 100,000 Hz

Infrasonic Waves Frequencies below 20 Hz You may feel these even though you cannot hear them Examples: Wind, Heavy Machinery, Earthquakes

Doppler Effect Change in pitch or frequency due to a moving object Example: Racetrack The car sounds louder as it approaches you and quieter as it moves away from you.

Chapter 12 Sound Section 3 Music

Music vs. Noise Noise has random patterns and pitches Music has specific patterns and pitches

Music Sounds are deliberately placed in a certain, regular pattern

Natural Frequencies Every material or object has a set of frequencies at which it vibrates Called its “natural frequency”

Natural Frequencies Depends on: Thickness 2. Length 3. Material 4. How tightly its stretched

Music and Resonance Sound of instrument is amplified by resonance This causes the instrument to absorb energy and vibrate at its natural frequency Air makes the sound louder

Sound Quality Differences among sounds of the same pitch and loudness

Sound Quality Object could be made to vibrate at frequencies other than their natural frequency. Makes sound waves with more than one frequency.

Overtones You only hear one of many frequencies made by an instrument. Not all frequencies are the same intensity.

Overtones Vibration whose frequency is a multiple of the fundamental frequency (the main tone played and heard)

Musical Instruments What are some examples of musical instruments?

Musical Instruments Strings: These instruments contain resonators (hollow chamber) to amplify the sound.

Musical Instruments Brass and Woodwinds *Rely on vibration of air to make music *Length of the vibrating tube of air determines the pitch of the sound

Musical Instruments Percussion *Consists of a membrane that is stretched over a resonator. *When membrane is struck, it causes the air inside to vibrate. * Makes sound

Beats These occur when sound waves of different frequencies combine.

Chapter 11 Sound Section 4 Using Sound

Reverberations Echoing effect Produced by reflections of sound

Reverberations Could ruin a concert or musical performance Concert halls must be designed to reduce the effect of this

Acoustics The study of sound Scientists and engineers who specialize in this design concert halls

Reducing Reverberation Soft, porous materials reduce reverberation Example: Drapes, carpet, cushioned seats

Echolocation Using sounds and sound waves to determine the location of an object What animal uses echolocation?

Sonar System that uses underwater sound waves to detect objects

Sonar In 1988 this was used to locate the Central America, a ship that had disappeared 140 years ago in a hurricane near South Carolina’s coast. It contained gold estimated to be worth $1 billion dollars. It was found 2,400 m under water.

How Sonar Works First: Sound pulse is sent to bottom of ocean Second: Sound wave is reflected when it hits something solid Third: Underwater microphone ( hydrophone) picks up signal

How Sonar Works Finally: Speed of sound in water is known. Distance of object is calculated by measuring time between when signal was sent and when it was received back.

Use of Ultrasonic Waves Break up dirt build up in jewelry Clean glassware in chemistry 3. Medicine

Ultrasound in Medicine Name one thing ultrasonic waves are used for in medicine.

Ultrasound Imaging The ultrasonic sound waves are reflected off the targeted organs or tissues and they are used to produce electrical signals. A computer converts these signals into video images (sonograms).

Ultrasound Imaging This type of imaging only works on soft tissue. Hard tissue, bones, and air absorb the ultrasonic waves.

Treating with Ultrasound Physicians now use ultrasonic sound waves to break up kidney stones.