2. Chapter 20 Sound

3. 1. ORIGIN OF SOUND The frequency of a sound wave is the same as the frequency of the source of the sound wave. Demo - Oscillator and speaker

4. The human hearing range is about 20 Hz - 20,000 Hz. infrasonic. Frequencies below 20 Hz are Frequencies above 20,000 Hz are ultrasonic.

5. 2. NATURE OF SOUND IN AIR Video - Tuning Fork Demo - Strobed Tuning Fork Sound in air is longitudinal with Compressions (Condensations) and Rarefactions Demo - Vortex Box

6. 3. MEDIA THAT TRANSMIT SOUND Air is most common but is a poor conductor. Solids and liquids are good conductors. A medium is required. Video - Vacuum Pump Video - Vacuum Pump (plus next 3 videos) (plus next 3 videos)

7. 4.SPEED OF SOUND IN AIR Much slower than light Video - Lumberjack Video - Lumberjack Video - Thunder and Lightning Video - Thunder and Lightning Video - Explosion Video - Explosion Depends on wind, temperature, humidity Does not depend on frequency

8. At 0 o C (dry air) v = 1090 ft/s = 750 mi/hr= 330 m/s increases with humidity increases with temperature is faster in liquids and solids How v varies:

9. prolonging of sound by reflection Rumble of distant thunder (several reflections from different distances) 5.REFLECTION OF SOUND Occurs anytime waves change media. Example:Echoes Example: Reverberation -

10. What is not reflected is transmitted and absorbed. Examples: San Francisco Symphony Hall Back of lecture room The study of sound properties is acoustics.

11. 6.REFRACTION OF SOUND When different parts of a wave front move at different speeds, the wave front will bend. This bending is known as refraction. It occurs when different parts of a wave front are traveling in different media.

12. Warm Air Cool Air

13. Other Examples Thunder and lightning Sometimes distant lightning is not heard well. Other times it is. Submarines and Sonar Refraction due to thermal gradients can “hide” submarines. Ultrasound in medicine Ultrasound echo and dolphins

14. 7.ENERGY IN SOUND WAVES Energy in sound is weak when compared to the energy in light. The human ear is a remarkable detector. 10 million people speaking at the same time produce approximately enough energy to light one flashlight.

15. High frequencies of sound in air more easily lose their energies to thermal energy than do low frequencies. That is why low frequencies can be heard farther away.

16. 8.FORCED VIBRATIONS Demo - Tuning Fork Touching a Table Demo - Tuning Fork Touching a Table Sound is intensified because of the larger surface area that can vibrate the air. The surface is forced to vibrate at the frequency of the tuning fork. (It is not a resonance phenomenon.) Examples: Musical sounding boards

17. 9.NATURAL FREQUENCY Demo - Drop Different Sounding Objects Demo - Drop Different Sounding Objects Objects have natural frequencies at which they vibrate. The natural frequency depends on elasticity and shape. Demo - Gravity Chimes Demo - Gravity Chimes Demo – Boomwhackers Demo – Boomwhackers Demo

19. 10. RESONANCE Resonance occurs when successive impulses are applied to a vibrating object in time with its natural frequency. Result - increased amplitude Examples: Swinging Marching on a bridge (rout step or break step)

20. Video - Matched Tuning Forks Video - Tuning Fork on Guitar Video - Breaking Glass Demo - Matched Tuning Forks Demo - Singing Glass Glass armonicaGlass armonica by Ben Franklin Glass armonica

21. Demo - Vibrating Rod Demo - Vibrating Plate Demo - Fog Horn Submultiples of the natural frequency also produce resonance. Demo - 256 & 512 Hz Tuning Forks Video - Tacoma Narrows Bridge Note:

22. 11.INTERFERENCE Defined in Chapter 19 Demo - Oscillator & Two Speakers Demo - Oscillator & Two Speakers Slide - Oscillator & Two Speakers Slide - Oscillator & Two Speakers Slide Examples: Dead spots in theaters and music halls Anti-noise technology

23. 12. Beats Fluctuating loudness due to two tones of slightly different frequencies that are sounded together (tremolo) It is an interference effect. Beats/s = difference in frequencies Musical instruments are tuned using beats. Dolphins use beats and Doppler effect.

24. Demo - Vibrating Rods Demo - Two Combs on Overhead Demo - Two Oscillators & Two Speakers Demo - Guitar

25. Constructive Interference Destructive Interference Consider two waves of slightly different frequencies traveling together.

26. RADIO BROADCASTS AM - 535 kHz to 1605 kHz FM -88 MHz to 108 MHz

27. Chapter 20 Review Questions

28. Frequencies of sound that are too high for the human ear to hear are called (a) faster than the speed of sound (b) supersonic (c) infrasonic (d) ultrasonic (e) subsonic (d) ultrasonic

29. For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso? (a) Galveston (b) El Paso (c) same speed in either city (a) Galveston

30. The bending of sound through air of uneven temperature is called (a) reflection (b) refraction (c) interference (d) reverberation (e) resonance (b) refraction

31. Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in feet is the thunder cloud? (a) 10,500 (b) 5280 (c) 1050 (d) 5250 (e) 105 (a) 10,500

32. A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard? (a) 255 (b) 510 (c) 10 (d) 250 (e) 260 (c) 10

33. (a) the lowest frequency had a node in the middle (b) the vibration was longitudinal (c) there were antinodes at the ends (d) the lowest frequency had a wavelength (in the rod) equal to the length of the rod Which of the following isn’t true concerning the metal rod that I vibrated in class by stroking it along its length?

34. Back