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The Physics of Sound Wave a disturbance that transfers energy from place to place. The material through which a wave travels is called a medium. Ex. Gases (air), liquids (water) and solids (rope) Waves that require a medium through which to travel are called mechanical waves. TRANSVERSE A wave that moves the medium in a direction perpendicular to the direction in which the wave travels. LONGITUDINAL A wave that moves a medium in a direction parallel to the direction in which the wave travels. Define Sound A disturbance that travels through a medium as a longitudinal wave. The Physics of Sound Longitudinal Wave The Physics of Sound How does sound travel? 1. Sound waves carry energy through a medium. 2. Each particle of the medium vibrates as the disturbance passes. 3. When the disturbance reaches your ears, you hear the sound. What is an echo? • A reflected sound wave is called an ECHO. • Reflection – when an object or a wave hits a surface through which it cannot pass, it bounces back. Explain why you don’t always here an echo? • There are often soft materials that absorb the sound waves in a room What are two ways sound diffracts? 1. Through an opening in a barrier such as a doorway or 2. Bend around corners Diffraction - the spreading or bending of a wave around a corner. What is the Speed of Sound • 343 m/s in air at 20°C Three factors that affect speed 1. Elasticity 2. Density 3. Temperature How does elasticity affect speed of sound? • The more elastic the faster sound will travel in the medium – Travels fastest in solids – Travels slower in liquids and gases because they are usually not as elastic How does density affect speed of sound? • Sound travels slower the denser the medium How does temperature affect speed of sound? • Sound travels more slowly at lower temperatures than at higher temperatures Properties of Sound Define loudness Loudness – describes what you hear and is measured in decibels (dB) Sound depends on 2 factors 1. 2. The amount of energy it takes to make the sound The distance from the source of the sound Explain how energy and distance affect loudness Energy – the greater the energy the louder the sound – larger amplitude = larger sound Distance – loudness increases the closer you are to the source – a sound wave of greater intensity sounds louder How is Sound Measured? DECIBEL SCALE 100 70 40 0 10 18 80 110 120 What is Pitch? • Pitch – a description of how high or how low the sound seems to a person How does Frequency affect pitch? – Depends on the frequency of the sound wave • • high frequency = high pitch low frequency = low pitch How do we change the pitch of our voice? • • • use vocal cords located in larynx to change sounds stretched vocal cords = higher frequency sound with high pitch relaxed vocal cords = lower frequency sound with low pitch What is the Doppler Effect the change in frequency due to the relative motion of the wave source and the observer The observed frequency is higher when the source and observer are getting closer. The observed frequency is lower when the source and observer are getting farther away. What causes the Doppler Effect? 1. when a sound source moves, the frequency of the waves changes because the motion of the source adds to the motion of the waves. 2. as source moves toward listener the frequency of the waves is higher (ex. Ball) Click here and here to run simulations of the Doppler Effect. The Doppler Effect can be evident for all types of waves – including light, sound, water, etc… Anatomy of the Human Ear Anatomy of the Human Ear anvil - (also called the incus) a tiny bone that passes vibrations from the hammer to the stirrup. cochlea - a spiral-shaped, fluid-filled inner ear structure; it is lined with cilia (tiny hairs) that move when vibrated and cause a nerve impulse to form. eardrum - (also called the tympanic membrane) a thin membrane that vibrates when sound waves reach it. Eustachian tube - a tube that connects the middle ear to the back of the nose; it equalizes the pressure between the middle ear and the air outside. When you "pop" your ears as you change altitude (going up a mountain or in an airplane), you are equalizing the air pressure in your middle ear. hammer - (also called the malleus) a tiny bone that passes vibrations from the eardrum to the anvil. nerves - these carry electro-chemical signals from the inner ear (the cochlea) to the brain. outer ear canal - the tube through which sound travels to the eardrum. pinna - (also called the auricle) the visible part of the outer ear. It collects sound and directs it into the outer ear canal semicircular canals - three loops of fluid-filled tubes that are attached to the cochlea in the inner ear. They help us maintain our sense of balance. stirrup - (also called the stapes) a tiny, U-shaped bone that passes vibrations from the stirrup to the cochlea. This is the smallest bone in the human body (it is 0.25 to 0.33 cm long). How does Human Hearing Work? sound wave vibrates ear drum amplified by bones (Hammer, Anvil , Stirrup) converted to nerve impulses in cochlea by cillia Healthy Cochlea The cilia ( sensory hairs) appear normal Damaged Cochlea Loss of cilia as a result of Noise Why does hearing loss occur? • Damaged ear drum, infections, extended exposure to loud noise and age • Most common form is gradual due aging. Cillia in ears die and no longer send signals to brain. Name and describe 3 ways sound is used? • Echolocation – the use of reflected sound waves to determine distances or locate objects. • Some animals, including bats and dolphins, use echolocation to navigate and to find food. Using Sound • Ultrasound technologies such as sonar and ultrasound imaging are used to observe things that cannot be seen directly. Using Sound Ultrasound imaging – devices send ultrasound waves into the body and detect the reflected sound waves. The device uses the reflected ultrasound waves to create a picture called a sonogram. Sonar – a system that uses reflected sound waves to detect and locate objects underwater. • Sonar is used to determine the depth of water, to map the ocean floor, and to locate sunken ships, schools of fish, and other objects in the ocean. “Seeing” with Sound Medical Imaging SONAR “Sound Navigation Ranging” • 1. Draw and Label the parts of the human ear • 2. Explain how human hearing works • 3 What are some causes of hearing loss? • 4. What is the most common cause of hearing loss? Explain what happens to the ears as we age. • 5. Name and describe 3 uses of sound.