Chapter 21 Sound What is sound Sound is

Chapter 21: Sound

What is sound? • Sound is a form of energy produced by the vibration of matter. • Sound is a compressional or longitudinal wave –Ex. Spring • The particles of the substance vibrate back and forth along the path that the sound wave travels

What is sound? • Sound is transmitted through solids, liquids, and gases (air). –But the air does not travel with the sound

• Sound is transmitted better through solids and liquids. Why? –More dense • Gases transmits sound a lot farther than a solid and liquid. Why? –Less dense; not as many particles to interfere.

• So what causes sounds to travel better through some substances and not others? –The greater the elasticity, the greater the speed. –The greater the density, the slower the speed. –The best conductors of sound are elastic substances.

• Sound can not be transmitted through a vacuum. –Sound needs a medium in order for it to be transmitted. • Radio waves can travel through a vacuum; no medium is needed. –This is why astronauts can use radio signals to talk in space.

Speed of Sound • 344 m/s in air at 20°C • Depends on: – Type of medium • travels better through liquids and solids • can’t travel through a vacuum – Temperature of medium • travels faster at higher temps

How you detect sound • Your ears change sound waves into electrical signals • Outer ear: pinna (collects sound waves and directs them into the ear canal)

How you detect sound • Middle Ear: increases the size of the vibrations (hammer, anvil, stirrup-3 bones) • Ear drum: tympanum (Vibrates the ear drum) • Inner Ear: vibrations created by sound are changed into electrical signals for the brain to interpret (cochlea)

Properties of Sound • Speed of sound is affected by the medium it travels through • Temperature affects sound – The cooler the medium the slower the sound travels – The warmer the medium the faster the sound travels

Properties of Sound • Pitch – highness or lowness of a sound – depends on frequency of sound wave – human range: 20 20, 000 Hz – High frequency = high pitch – Low frequency = low pitch ultrasonic waves subsonic waves

FREQUENCIES YOU CANNOT HEAR • Ultrasonic: higher than 20, 000 Hz Uses: clean jewelry, medical applications • Infrasonic: lower than 20 Hz Found: in the atmosphere and in the crust when plates move; also an indication motion sickness

Human Hearing • Intensity – Volume, or loudness, of sound: the measure of how well a sound can be heard – depends on energy (amplitude) of sound wave – measured in decibels (d. B) – Above 120 d. B can cause hearing loss.

Human Hearing DECIBEL SCALE 100 70 40 0 10 18 80 110 120

Doppler Effect • Doppler Effect – change in wave frequency caused by a moving wave source or when the observer of the sound moves w moving toward you pitch sounds higher w moving away from you - pitch sounds lower

Seeing with Sound • Sound waves are invisible • A device known as an oscilloscope graphs representations of sound waves

Seeing with Sound • Ultrasonic waves - above 20, 000 Hz Medical Imaging SONAR “Sound Navigation and Ranging”

Reflection of Sound Waves • Echoes are reflected sound waves – The strength of the reflection depends on the reflecting surface – Are best reflected off smooth hard surfaces • Echolocation: process using reflected sound waves to find objects – Bats – Whales – SONAR – Ultrasonography

Interference • Interference – the ability of 2 or more waves to combine to form a new wave Constructive - louder Destructive - softer

Interference • Beats – variations in sound intensity produced by 2 slightly different frequencies – both constructive and destructive interference occur

Cool Interference Examples: • The Sound Barrier: the point at which the source of a sound accelerates to the speed of sound • Sonic Booms: the explosive sound heard when a shock wave reaches your ears • 1 st time sound barrier broken: Oct. 14, 1947 by Chuck Yeager (speed of sound is called Mach 1); so Mach 6 is going 6 times the speed of sound

Chuck Yeager Breaks the Sound Barrier

Sound Barrier and Sonic Booms

Resonance • Forced Vibration – when one vibrating object forces another object to vibrate at the same frequency – results in a louder sound because a greater surface area is vibrating – used in guitars, pianos, etc.

Resonance • Resonance – special case of forced vibration – object is induced to vibrate at its natural frequency

Harmonics • Fundamental – the lowest natural frequency of an object • Overtones – multiples of the fundamental frequency

Music vs. Noise • Music – specific pitches and sound quality – regular pattern • Noise – no definite pitch – no set pattern – Any sound that is a random mix of frequencies or pitches

Acoustics • Acoustics – the study of sound • Reverberation – echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.