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

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

Less dense; not as many particles to interfere. 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.

The greater the elasticity, the greater the speed. 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 needs a medium in order for it to be transmitted. 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

Your ears change sound waves into electrical signals 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)

Ear drum: tympanum (Vibrates the ear drum) 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 (dB) Above 120 dB can cause hearing loss.

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

Doppler Effect moving toward you - pitch sounds higher change in wave frequency caused by a moving wave source or when the observer of the sound moves moving toward you - pitch sounds higher 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 1st 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 Overtones the lowest natural frequency of an object Overtones multiples of the fundamental frequency

Music vs. Noise Music Noise 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 Reverberation the study of sound echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.