Sound and Related Topics

1. Sound and Related Topics Let’s Hear More About It

2. Sound “ideas” • Compressional wave with air as the medium • compression -- molecules are squished together creating areas of high pressure. • rarefaction -- molecules are spread apart creating areas of low pressure.

3. Example:

4. Sound waves need three things: • A source ; something vibrating. • A medium; something for the wave to travel in. • A receiver; something to detect the vibration.

5. If the vibration is: • Regular and pleasing, we call it music • Irregular and annoying, we call it noise.

6. The medium dictates the velocity: • Fastest in more dense mediums, and more elastic mediums. [bucket] • In air sound travels at ~331.5m/s at 0oC, and increases with Temperature. • TOOLBOX: Speed of Sound 340 m/s • ~ 760.5 miles/hour • MACH 1 • In water it travels at ~ 1500m/s, while • In some solids, it can travel at ~5000 m/s.

7. Gases Material v (m/s) Hydrogen (0°C) 1286 Helium (0°C) 972 Air (20°C) 343 Air (0°C) 331 Speed of Sound in Various Materials

8. Liquids at 25°C Material v (m/s) Glycerol 1904 Sea water 1533 Water 1493 Mercury 1450 Kerosene 1324 Methyl alcohol 1143 Carbon tetrachloride 926 Liquids

9. Solids Material v (m/s) Diamond 12000 Pyrex glass 5640 Iron 5130 Aluminum 5100 Brass 4700 Copper 3560 Gold 3240 Lucite 2680 Lead 1322 Rubber 1600 Solids

10. Sonic BOOM • A Sonic boom is a noise similar to thunder. It is caused by an object moving faster than sound. • An aircraft traveling through the atmosphere continuously produces waves similar to the water waves boat. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves. As an aircraft flies at supersonic speeds it is continually generating shock waves, dropping sonic boom along its flight path, similar to someone dropping objects from a moving vehicle. If the plane makes a sharp turn or pulls up, the boom will hit the ground in front of the aircraft.

11. Sonic BOOM

12. Sonic BOOM

13. Sound Wave Characteristics:

14. Wavelength: • The distance between 2 successive compressions (or 2 successive rarefactions).

15. Amplitude: • Relates to the intensity or loudness of the sound. • An indication of the energy of the wave.

16. Amplitude: • Measured in units called decibels (dB’s). 120 dB’s is the human ear’s pain threshold

17. Frequency: • Relates to the pitch (or tone). • The higher the frequency, the higher the pitch.

18. The human ear. • Very detailed construction. • Range is from 20 hertz to 20,000 hertz.. • Below 20 Hz -- infrasonic sounds. • Above 20,000 Hz -- ultrasonic,

19. Uses of Sound

20. Infrasonic (Subsonic) • sound frequencies below 20 Hz • Earthquakes produce infrasonic sound • Elephants communicate through infrasonic • VERY LOW SOUNDS

21. Ultrasonic • sound frequencies above 20,000 Hz • Examples: Echolocation – Bats, Whales • Examples: SONAR • Medical Uses

22. SONAR • (So)und (Na)vigation and (R)anging • Sound sent underwater, bounces back • Can be used over long distances • 4 sites cover 80% of the ocean

23. RADAR • (Ra)dio (D)etecting (a)nd (R)anging • Radio waves – Not Sound Waves • We’ll come back to this topic during EM waves

24. Sound Wave Phenomena

25. Doppler Effect • A Change in pitch or frequency due to a moving wave source. • In front of object: High frequency, high pitch, short wavelength • Behind object: Low frequency, low pitch, long wavelength. • Sound waves get pushed together, or spread out, changing pitch

26. Doppler Effect • Doppler Effect Applet

27. Resonance: • When the vibration of the source matches the natural frequency of the object, causing it to start resonating (vibrating). • All objects have a natural frequency • Resonance is Vital to the proper functioning of most musical instruments.

28. Resonance: • Objects vibrate more and more as they absorb more natural frequency vibrations (constructive interference). If they absorb enough energy, they will break.

29. How You HEAR!! • The outer Ear: Where sound waves are gathered -Visible part (pinna) -Ear Canal -Ear Drum Channel sound waves to eardrum which vibrates

30. How You HEAR!! • Vibrating ear drum causes 3 tiny bones to vibrate, which amplify the sound. • The Middle Ear : Sound is amplified -Hammer -Anvil -Stirrup

31. How You HEAR!! • The Inner Ear: Converts vibrations to nerve impulses -Cochlea Auditory Nerve Semi Circular Canals Eustachian Tube • Vibrations from middle ear vibrate the cochlea, which converts vibrations to nerve impulses

32. How You HEAR!!

33. Hearing Problems • Hearing Loss: tiny hairs (cilla) in cochlea are destroyed or damaged, often by loud sounds. • Deafness: Caused by failure of eardrum or tiny bones to vibrate. Problems with cochlea. • Dizziness: Caused by problems with semi circular canals - Vertigo • Ear Infection – Eustachian tube is close to nasal cavity

34. MUSIC • Noise – random waves frequencies, and pitches • Music – sound in a regular pattern

35. Every Musical note has a certain frequency, which gives it a distinct pitch. Music • Arrange the notes in a familiar or pleasing pattern and……

36. Music • Musical instruments contain strings, membranes, columns of air – something that vibrates at a natural frequency to create pitch. • Remember Resonance - Musical instruments contain a resonator which amplifies the sound.

37. Fundamental Frequency : The lowest frequency. Visit the Sound Lab Fundamentals and Overtones: • Overtones: Also called harmonics, these frequencies are whole number ratios of the fundamental

38. Sound Quality: • Quality: differences among sounds of the same pitch • Middle C for a Flute versus a Piano

39. Sound Quality • The overall sound “envelop” (the combination of the fundamental and overtones) makes the sounds distinguishable

40. Interference; • When two sound waves meet at the same time and spot. • The effect is called Beats: A rhythmic variation in amplitude. • Visit the Sound Lab • Beat Frequency = Difference in the two frequencies.

41. The end of the the story .