Chapter 16 Sound Waves

I.Sound is a wave. A. Sound is a type of mechanical wave. 1. produced by a vibrating object and travels through matter 2. disturbances are vibrations-rapid back and forth motions 3. medium vibrates in the same direction as the wave travels and transfer energy 4. How Sound Waves Are Produced a. started by vibrations that send out waves in all directions Example: vocal cords- relax when you breathe to allow air to pass through the windpipe; they tense up when you are about to sing or speak

5. How Sound Waves Are Detected a. Shape of the ear (like a satellite dish) helps collect sound waves b. Reflected into the ear canal (tiny tube) c. Waves strike the eardrum ( thin skin-like membrane at the end of the ear canal) and they vibrate. d. Vibrations transfer from the eardrum through the tiny bones in the middle ear (hammer, anvil and stirrup.) e. Vibrations reach the cochlea (30,000 hair cells) and vibrate (bend) the tiny hairs causing the cells to send impulses along the nerves to the brain. f. When your brain processes these signals, you HEAR A SOUND!

B. Sound waves vibrate particles. 1. You cannot see the motion of waves in air. 2. Imagine striking a drum: a. Drum skin vibrates very rapidly (pushing in and out) and pushes against particles in the air. Particles become bunched together (compressions). b. When the skin is pushed in the opposite direction, it leaves an open space for the particles to rush back in and fill it. c. A listener hears all of these vibrations. P. 520

***A vacuum is empty space and has no particles so sound cannot travel through it! C. The speed of sound depends on its medium. 1. Sound travels more slowly than light and at different speeds. 2. Two factors affect the speed of sound: type of medium and the temperature 3. The Effect of the Material a. Sound waves travel faster through liquids than in air because liquids are denser (closely packed) ***Divers would hear a sound quicker underwater than people above water. b. Sound waves travel through elastic solids as well.

2. The Effect of Temperature a. Sound travels faster through higher temperatures (hot air). Example: Yelling outside on a hot day very a cold winter morning 16.1

II. Frequency determines pitch. A. Pitch depends on the frequency of a sound wave. 1. Pitch- high or low of sounds 2. high frequency=short wavelengths= fast vibrations= high pitch (and vice versa) 3. High and Low Frequencies a. Once complete wave is a cycle b. Unit of measurement for frequency and pitch is HERTZ c. Human hearing range is 20-20,000Hz d. Infrasound- ranges below 20 hertz Example: elephants e. Ultrasound- ranges above 20,000hertz Example: dogs, bats, chimpanzees and dolphins

4. Natural Frequencies a. The frequency at which an object vibrates b. Constructive interference- when two different sound waves of the same natural frequency encounter one another; amplitudes add and the sound is stronger (resonance) 5. Sound Quality a. Each musical instrument and human voice has its own particular sound- sound quality. b. Timbre (sound quality) is explained because it’s a combination of waves. You hear the fundamental tone. c. Overtones- higher frequency pitches d. Affected by starts and stops- human voice starts gently (p. 529 Oscilloscope)

B. The motion of the source of a sound affects its pitch. *** motion of the source of a sound affects the pitch Example: the pitch drops when an ambulance passes by you coming from behind. 1. The Doppler Effect *** The change in perceived pitch that occurs when the source of receiver of a sound is moving Experiment: p Frequency and Pitch a. Sound waves that hit your ears are closer together so the pitch and frequency is higher b. As the sound moves farther away, sound waves still come to you but they are farther apart and lower in pitch.

III. Intensity determines loudness. A.Intensity depends on the amplitude of a sound wave. 1. the more energy a wave carries, the more intense and the louder 2. measured in decibels 3. greater the amplitude, more intensity and the louder it will be B. The intensity of sound can be controlled. 1. Sound waves get weaker and weaker until sound in undetected. (amplitude decrease but frequency and pitch stay the same) 2. sound intensity is changed by adding or removing energy (changing amplitude) Example: mufflers on cars (makes it sound lower)

3. Amplification a. Make it bigger b. Increases the strength of the electrical signal Example: adjusting stereo volume 4. Acoustics a. Scientific study of sound b. How sound is produced and received c. How sound waves behave inside a space Example: using acoustical tiles of different shapes to absorb or redirect some of the energy of sound waves C. Intense sound can damage hearing 1. The sensitivity of hair cells of the cochlea make hearing possible and makes it easy to damage cells as well. 2. Noises above 130dB are especially dangerous; 140dB are even painful. Example: Some loud factories are required to provide ear plugs for ear protection to employees.

IV. Sound has many uses. A.Ultrasound waves are used to detect objects. 1.Echolocation a. Sending out ultrasound waves and interpreting the returning sound echoes b. Helps animals find their prey or objects in front of them Example: bats and dolphins p. 539

Echolocation Bat Music Video

2. Sonar a. Instruments that use sound waves (echolocation) to locate objects b. Sound navigation and ranging c. Send out ultrasound waves and use the echoes to produce an image on the screen Examples: locating submarines during war, fishing boats, to map the sea floor, find ancient sunken ships 3. Medical Uses of Ultrasound *** Not heard by humans and used at high intensities Examples: break up kidney stones, see used to clean medical equipment, to see inside internal organs, detect the movement of fluids (blood flow) through the body, checking the health of a fetus during pregnancy

B. Sound waves can produce music. a. Clear pitches or rhythms b. Vibrate at their natural frequencies c. Some have different parts that vibrate to make different pitches d. Stringed, wind and percussion- 3 main types (electronic- 4 th type) Examples: p. 541 C. Sound can be recorded and reproduced. 1. The Telephone a. Long distance voice communication b. Translates and the then reproduces sounds See p Recorded Sound a. Occurs in real time b. sound waves turned in to electrical signals See p. 543