Sound Waves

1. Sound Waves How We Hear Properties of Sound Using Sound

2. What is the doctor really doing when she says, “I’m going to listen to your heart”? • The vibrations of the heart, travel to the skin, which create waves which travel up the tubing to the doctor's ears

3. Page 4- Benchmark 3.3:THE STUDENT WILL DESCRIBE HOW WAVES MOVE AT DIFFERENT SPEEDS IN DIFFERENT MATERIALS. [P8C2]

4. What affects the speed (v)of the wave?Elasticity of Medium • Elasticity-the tendency of a material to maintain its shape and not deform whenever a force or stress is applied to it • More elastic = the faster the wave travels • Waves travel faster through solids than they do liquids, and faster in liquids than in gases  • vsolids > vliquids > vgases • Which material is more elastic? • Steel vs. Rubber? • Steel!! • Steel = maintains shape = high elasticity • Rubber = deforms easily = low elasticity • The molecules of elastic materials are very attracted to each other, so the particles return to their resting position quickly, and are ready to move again more quickly. So, they vibrate at higher speeds!

5. It is easier for sound waves to go through solids than through liquids because the molecules are closer together and more tightly bonded in solids. • It is harder for sound to pass through gases than through liquids, because gaseous molecules are farther apart. What affects the speed (v)of the wave?Medium - State of Matter • It is easier for sound waves to go through solids than through liquids because the molecules are closer together and more tightly bonded in solids. • It is harder for sound to pass through gases than through liquids, because gaseous molecules are farther apart. • The speed of sound is fastest in solid materials, slower in liquids, and even slower in gases • But what if we are only comparing gases (Helium vs. air)? • Sound travels faster in a less dense material than in a more dense material of the same state of matter • Sound waves travel 3x faster in Helium than in air—causes the high pitch voice! • Why? Helium molecules have less mass than air molecules!

6. What affects the speed (v)of the wave?Temperature of Medium • Hotter material = faster molecular motion = faster speed of sound • Colder material = slower molecular motion = slower speed of sound • Therefore, sound travels faster in warm air than in cool air

7. Bell Work: 10/12/08 • What is echolocation? • Do you think sound waves can break glass? Why or why not?

8. SOUND – Benchmarks & Standards

9. Page 2- Why can you hear someone knock on the door when you are on the other side? • When you knock on the door, the particles of the door vibrate. • The vibration creates sound waves that travel through the door. • When the sound waves reach the other side of the door, they make sound waves in the air on the far side.

10. Philosophy vs. Science- Page 2 If a tree falls in the forest and no living creature is there to hear it, does it make a sound? • NO. When a tree falls, the surrounding air (medium) is disturbed, causing sound waves. • When sound waves arrive at our ears they cause small bones in our ears to vibrate. These vibrations then cause nerve impulses to be sent to the brain where they are interpreted as sound. • If there is nobody there to perceive it occurring, then it could not exist as sound, only vibration.

11. Sound is a longitudinal & mechanical wave. • Energy moves in the same direction as the particles move & requires a medium to travel. • Sound waves are often pictured as if they were transverse, because it’s easier to picture.

12. Human Sound Production • Larynx- voice box at top of trachea; contains the vocal chords • Trachea- windpipe • Vocal chords- pair of thin tissue in your windpipe; vibrate and allow us to talk and sing • During speech lessons, teachers and deaf students often touched each other's throats to feel vocal chord vibrations.

13. Video: “How We Hear” • Questions: • What three bones are found inside your ear? • Describe the process in which humans hear from start to finish. • What happens to your hearing if the hairs in your ears die or become paralyzed? • What else might cause hearing loss?

14. What three bones are found inside your ear? • Hammer • Anvil • Stirrup hammer anvil stirrup

15. Describe the process in which humans hear from start to finish. • A sound wave is funneled through the outer earinto the middle ear canal. • Sound is amplified by the eardrum which vibrates when the wave hits it (The eardrum stretches across the ear like a drumhead). • The vibrations are transmitted to the three small bones: the hammer, anvil and stirrup. • These bones amplify the vibrations and send the energy to the fluid-filled cochlea in the inner ear. • The vibrations reach hair tipped cells that generate signals containing information (frequency, intensity and duration of the sound). • The stimulations of the tiny hairs send messages to the brain.

16. Human Hearing Outer ear Middle ear canal Vibrates ear drum Amplified by bones: Hammer, anvil, stirrup Inner ear Hair tipped cells Cochlea converts nerve impulses

17. Properties of Sound: Loudness • Loudness- describes what you actually hear; your perception of the intensity of a sound • Measured in decibels (dB) • Decibel (dB)- unit for measuring loudness of a sound wave • Decibel Scale- measures sound based on human hearing; which makes it one of the most unusual scientific scales • Threshold of hearing: 0 decibels • Threshold of pain: 120 decibels • Larger Amplitude = Louder sound

18. The Decibel Scale

19. How does sound cause hearing loss? Amplitude • The louder the sound, and the longer you listen to it, the more hearing you lose! • Intensity- How much energy passes through a given area in an amount of time • Loudness- the perception of how much energy a sound wave carries Sources of Hearing Loss • 33.7% = Prolonged Loud Noise/ Industrial Deafness • 28% = Age • 17.1% = Infection/Injury • 16.8% = Other • 4.4% = Born with Hearing Loss • If you wanted to graph this data, what type of graph best depicts percentages? Bar graph, line graph, or pie chart?

20. Bellwork: • What type of wave has crests and troughs? Describe the difference between a crest and a trough. • Crest - highest point of a transverse wave • Trough - lowest point of a transverse wave • What type of wave has compressions? What happens to molecules during a compression? • Compression - the molecules in the longitudinal wave are “compressed” together • What type of wave has rarefactions? What happens to the molecules during a rarefaction? • In a rarefaction, the molecules in the longitudinal wave become spread apart.

21. LIGHT – Benchmarks & Standards

22. Properties of Sound: Frequency • Frequency- the number of complete waves that pass a point in one second • Measured in Hertz (Hz) • 1 Hertz is equal to 1 wave per second • 100 Hz is equal to 100 waves per second • Human hearing: 20 Hz - 20,000 Hz High Frequency Low Frequency

23. Properties of Sound: Pitch • Pitch- description of how high or low the sound seems • Pitch depends on the frequency of the sound wave • Higher pitch = higher frequency = shorter wavelengths • Lower pitch = lower frequency = longer wavelengths • Medical Ultrasound • 1.0 - 20 MHz • Ultrasound • >20,000 Hz • Audible Sound (Human Hearing) • 20Hz-20,000 Hz • Infrasound • 0-20 Hz

24. Resonance • Natural Frequency- All objects vibrate naturally; the frequency at which the molecules in an object naturally vibrate; the frequency of the object depends on the shape & type of the object • Resonance- The increase in vibrations of an object when exposed to a sound wave whose frequency is equal to the natural frequency of the object • If the object is not flexible (i.e. crystal glass), the object will break (shattering of a glass) • MythBusters- “Breakstep Bridge” • Occasionally causes a bridge to collapse • Fundamental Frequency – the lowest frequency at which an object will vibrate

25. Mythbusters Video“Breaking Glass” • In this video, Adam and Jaime try to test the myth that a singer can break glass using only their voice.