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WHAT IS SOUND? • All sounds are created by vibrations A vibration is the complete backand-forth motion of an object. • A sound wave is a longitudinal wave caused by vibrations and carried through a substance • Sound waves travel in all directions away from their source. • Air or other matter does not travel with the sound waves. Why not…? MEDIUM • All sound waves require a medium. •A medium is a substance through which a wave can travel. Sound waves vibrate the eardrum The eardrum vibrates the hammer, anvil and stirrup The stirrup vibrates the oval window. The liquid makes hairs inside bend. The oval window makes waves in the cochlear liquid. Hair stimulates nerves which send messages to the brain. Jay-Z, Don’t these earrings make my outer ear look so fly? Check for Understanding… • What is the job of the outer ear? • What is the job of the bones in the middle ear? • What is the job of the inner ear? OUTER EAR… • COLLECT & DIRECT! I collect da ladies and direct da videos! MIDDLE EAR… • INCREASE THE SIZE OF VIBRATIONS. How…? (Hint: they are a type of simple machine!) INNER EAR… • Convert vibrations into electric signals. Hearing Loss & Deafness • Exposure to loud sounds can cause Tinnitus. • The hair cells in the cochlea are permanently damaged. PROTECT YOUR HEARING! PROPERTIES OF SOUND • SPEED • PITCH & FREQUENCY • LOUDNESS & AMPLITUDE SPEED Look at the chart…In what state of matter does sound travel fastest? What is the relationship between temperature and speed of sound? - The Nature of Sound Temperature and the Speed of Sound •The speed of sound in dry air changes as the temperature changes. The graph shows data for the speed of sound in air at temperatures from –10ºC to 20ºC. FREQUENCY & PITCH Remember –frequency is the number of waves in a given time. Frequency is measured in Hertz. 1 Hz = 1 wave/ second. Low note on a piano 40 Hz Screech of a bat 10,000 Hz Frequency & Hearing • Sounds too high to hear are called ultrasonic The Doppler Effect The APPARENT change in the frequency of a sound caused by the motion of either the listener or the source. What is sound? 1 The Doppler Effect • The change in frequency that occurs when a source of sound is moving relative to a listener is called the Doppler effect. • The Doppler effect occurs whether the sound source or the listener is moving. What is sound? 1 The Doppler Effect • As you move closer you encounter each sound wave a little earlier than you would if you were sitting still, so the sound has a higher pitch. • When you move away from the sound, each sound wave takes a little longer to reach you. • You hear fewer wavelengths per second, which makes the sound lower in pitch. What is sound? 1 The Doppler Effect • Radar guns that are used to measure the speed of cars and baseball pitches also use the Doppler effect. • When the radio wave is reflected, its frequency changes depending on the speed of the object and whether it is moving toward the gun or away from it. • The radar gun uses the change in frequency of the reflected wave to determine the object’s speed. LOUDNESS & AMPLITUDE • Loudness is a measure of how well a sound can be heard. • Loudness is measure in decibels • The larger the amplitude of a sound wave the louder the sound. • An increase in the loudness of a sound of 10 dB means that the energy carried by the sound has increased ten times, but an increase of 20 dB means that the sound carries 100 times more energy. • Hearing damage begins to occur at sound levels of about 85 dB. • The amount of damage depends on the frequencies of the sound and the length of time a person is exposed to the sound. “Seeing” Amplitude & Frequency INTERACTIONS OF SOUND WAVES - The Nature of Sound Interactions of Sound Waves • Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with each other. What is sound? 1 Echoes • A reflected sound wave is called an echo. • If the distance between you and a reflecting surface is great enough, you might hear the echo of your voice. • This is because it might take a few seconds for the sound to travel to the reflecting surface and back to your ears. What is sound? 1 Echoes • Sonar systems used sound waves to map objects underwater. What is sound? 1 Echoes • By measuring the length of time between emitting a pulse of sound and hearing its echo off the ocean floor, the distance to the ocean floor can be measured. 1 Echolocation Some animals use a method called echolocation to navigate and hunt. Bats, for example, emit high-pitched squeaks and listen for the echoes. The type of echo it hears helps the bat determine exactly where an insect is. What is sound? 1 Echolocation • People with visual impairments also use echolocation. • Using their ears, they can interpret echoes to estimate the size and shape of a room, for example. • Some animals, including bats and dolphins, use echolocation to navigate and to find food. 1 Using Sound Waves • Sound waves can be used to treat certain medical problems. • A process called ultrasound uses highfrequency sound waves as an alternative to some surgeries. What is sound? 1 Using Sound Waves • For example, some people develop small, hard deposits in their kidneys or gallbladders. • A doctor can focus ultrasound waves at the kidney or gallbladder. • The ultrasound waves cause the deposits to vibrate rapidly until they break apart into small pieces. What is sound? 1 Using Sound Waves • Ultrasound can be used to make images of the inside of the body. • One common use of ultrasound is to examine a developing fetus. • Also, ultrasound along with the Doppler effect can be used to examine the functioning of the heart. 2 Resonance • Sometimes sound waves cause an object to vibrate. • When a tuning fork is struck, it vibrates at its natural frequency and produces a sound wave with the same frequency. 2 Resonance • Suppose you have two tuning forks with the same natural frequency. • You strike one tuning fork, and the sound waves it produces strike the other tuning fork. • These sound waves would cause the tuning fork that wasn’t struck to absorb energy and vibrate. • This is an example of resonance. Resonance • Resonance occurs when an object is made to vibrate at its natural frequencies by absorbing energy from a sound wave or another object vibrating at these frequencies. • Musical instruments use resonance to amplify their sounds. 2 Overtones • A tuning fork produces a single frequency, called a pure tone. • The notes produced by musical instruments are not pure tones. • Most objects have more than one natural frequency at which they can vibrate. • As a result, they produce sound waves of more than one frequency. 2 Overtones • If you play a single note on a guitar, the pitch that you hear is the lowest frequency produced by the vibrating string. • The lowest frequency produced by a vibrating object is the fundamental frequency. • The vibrating string also produces higher frequencies. Overtones • These higher frequencies are called overtones. • Overtones have frequencies that are multiples of the fundamental frequency. Overtones • The number and intensity of the overtones produced by each instrument are different and give instruments their distinctive sound quality. A sonic boom is the name for the explosive sound you hear when a shock wave reaches your ear. SOUND QUALITY • The result of several pitches mixing together is called sound quality. Sound quality differs when two instruments play the same note. MUSIC OR NOISE? Noise can be described as any sound, especially a nonmusical sound, that is a random mix of frequencies (or pitches). - How You Hear Sound The Human Ear • The outer ear funnels sound waves, the middle ear transmits the waves inward, and the inner ear transforms sound waves into a form that travels to your brain. http://www.scilinks.org/retrieve.asp