Section 4 Sound and Hearing

Properties of Sound Waves Sound waves are longitudinal waves — compressions and rarefactions that travel through a medium. Many behaviors of sound can be explained using a few properties— speed, intensity and loudness, and frequency and pitch.

Speed of Sound Speed of a wave depends on the medium it travels in The speed of sound is determined by the temperature, elasticity, and density of the medium through which the sound travels.

Speed of Sound Temperature: Low temperatures makes the medium vibrate slower, Hence slowing the speed of sound Elasticity: Solids are generally more elastic than liquids and liquids are generally more elastic than gases Density: If the medium is the same, the speed of sound is slower the more dense it is.

Intensity and Loudness The amount of energy carried by a wave in a certain amount of time Intensity determines the loudness of a sound Intensity scale is measured in the unit Decibel (dB) Over 140 dB is painful for humans Instant Perforation of Eardrum 160 dB

Frequency and Pitch Pitch: A description of a sound as high or low The pitch of a sound wave is determined by how the number of waves produced in a given time (Frequency) Thus the pitch of a sound depends on the frequency of waves

Frequency and Pitch Humans can hear from about 20 to 20,000 hertz Sounds higher than 20,000 hertz are known as Ultrasonic Sounds lower than 20 hertz are known as Infrasonic

Doppler Effect Occurs whenever there is motion between the source of a sound and its receiver Link If you are in front of the source the frequency is higher hence producing a higher pitch sound If you are behind the source the frequency is lower, hence producing a lower pitch sound

Doppler Effect

Sound Uses Sound has many applications in the medical field, cleaning, and locating objects.

Sonar Sound Navigation and Ranging High frequency ultrasonic waves used to see using sound. Research ships use this to find sunken ships. The Navy used it to map all of the worlds oceans, submarines use it to see, and battleships use it to find subs. Fishing boats use it to find fish. Cameras use it to automatically focus.

Images from SONAR Fish

USS Utah

Volcano on the sea floor

Ultrasonic Cleansing Used on objects that are too delicate to clean with sponges Jewelry, electronic components, delicate machine parts. Teeth are also cleaned ultrasonically

Ultrasonic Cleansing

Sound and Medicine Used to diagnose medical problems Used as an X-ray Used to take pictures of babies (Ultrasound) Used to destroy calcium build-ups in the body (kidney stones, gall stones)

Ultrasound Images

Kidney Stone It works like this!!

The Ear In humans, the organ of the body that detects sound is the ear. There are three parts to the human ear Outer Middle Inner

Outer Ear The outer ear acts a funnel for the sound waves entering the ear The sound waves are moved down the ear canal to the Eardrum (a lightly stretched membrane) The ear canal has wax in it to keep the eardrum moist Link

Middle Ear Contains the three smallest bones in the human body The Hammer – picks up the vibrations from the eardrum The Anvil – gets the vibrations from the hammer and transmits them to The Stirrup – it transmits its vibrations to another membrane

Inner Ear The vibrations are channeled into the Cochlea Cochlea – shaped like a snail shell contains a liquid and hundreds of cells connected to nerve fibers. These nerve fibers form one nerve that send impulses to the brain where it is interpreted as sound

Cochlea

How The Ear Works

Reviewing Concepts 1. List five properties used to explain the behavior of sound waves. 2. Name two uses for ultrasound. 3. What is the Doppler effect? 4. What are the ear’s three main regions? Describe the function of each region.