1. The Production of Sound Waves Every sound wave begins with a vibrating object, such as the vibrating prong of a tuning fork. Sound waves are longitudinal.

2. Frequency of Sound Waves Remember, frequency is defined as the number of cycles per second. infrasonic wavesultrasonic waves

3. Frequency and Pitch The frequency of an audible sound wave determines how high or low we perceive the sound to be, which is known as pitch. As the frequency of a sound wave increases, the pitch rises. The frequency of a wave is an objective quantity that can be measured, while pitch refers to how different frequencies are perceived by the human ear.

4. The Speed of Sound The speed of sound depends on the medium. – depends on how quickly one particle can transfer its motion to another particle. – For example, sound waves generally travel faster through solids than through gases because the molecules of a solid are closer together. The speed of sound in dry air can be calculated with the equation v = 331 + 0.6 T where T is the temperature in °C. As the humidity in the air builds, more lighter-mass water molecules are present and sound will travel faster than it would at the same temperature dry-air.

5. The Speed of Sound in Various Media

6. The Doppler Effect

7. Doppler Effect Stationary objectMoving Source

8. Doppler Effect Source moving with speed equal to speed of sound ( Mach 1 - breaking the sound barrier ) Source moving greater than the speed of sound (Mach 1.4 - supersonic) Sonic boom video

9. Sound Intensity The rate at which sound energy is transferred through a medium. Directly proportional to the power and inversely proportional to the distance from the source (same amount of energy spread over a larger area) Units = Watts/meter squared The intensity of a wave approximately determines its perceived loudness.

10. Conversion of Intensity to Decibel Level Loudness is not directly proportional to intensity but is approximately logarithmic in the human ear which means that if intensity doubles that does not mean that loudness doubles. Loudness is measured in decibels.

11. Sound Intensity, continued Human hearing depends on both the frequency and the intensity of sound waves. Sounds in the middle of the spectrum of frequencies can be heard more easily (at lower intensities) than those at lower and higher frequencies.

12. Wave Damping Waves losing energy to the medium as they travel Molecules in medium generate heat as they vibrate In general, low frequency waves travel further than high frequency waves because there is less energy transferred to the medium. Hence the use of low frequencies for fog horns.

13. Forced Vibrations Forced Vibrations and ResonanceResonance Each pendulum has a natural frequency (a frequency at which they vibrate more easily) based on its length. Resonance is when the frequency of a force applied matches the natural frequency of vibration of the object, resulting in a large amplitude of vibration. Resonance in wine glass

14. Tacoma Narrows Bridge Collapse "Gallopin' Gertie" Slender, elegant and graceful, the Tacoma Narrows Bridge stretched like a steel ribbon across Puget Sound in 1940. The third longest suspension span in the world opened on July 1st. Only four months later, the great span's short life ended in disaster. "Galloping Gertie," collapsed in a windstorm on November 7,1940. The bridge became famous as "the most dramatic failure in bridge engineering history." Now, it's also "one of the world's largest man-made reefs." The sunken remains of Galloping Gertie were placed on the National Register of Historic Places in 1992 to protect her from salvagers.

15. Standing Waves on a Vibrating String The vibrations on the string of a musical instrument usually consist of many standing waves, each of which has a different wavelength and frequency. The greatest possible wavelength on a string of length L is = 2L which produces the fundamental frequency (the lowest frequency of vibration). Just for fun!

16. Standing Waves on a Vibrating String The harmonic series is a series of frequencies that includes the fundamental frequency and multiples of the fundamental frequency. Earth harp

17. Practice: What is the fundamental frequency of a guitar string when the speed of waves on the string is 115. m/s and the string length is 70.0 cm? 50.0 cm? 35.0 cm? A violin string that is 50.0 cm long has a fundamental frequency of 440. Hz. What is the speed of the waves on this string? – What controls the speed of the wave on the string? What are the first three harmonics of a note produced on a 31.0 cm long violin string if waves on this string have a speed of 274.4 m/s?

18. Standing Waves in an Air Column

19. Harmonic Series of a Pipe Open at Both Ends If both ends of a pipe are open, there is an antinode at each end. All harmonics are present.

20. Harmonic Series of a Pipe Closed at One End If one end of a pipe is closed, there is a node at that end. With an antinode at one end and a node at the other end, a different set of standing waves occurs. In this case, only odd harmonics are present. Street music

21. Standing Waves in an Air Column

22. Practice: What are the first three harmonics in a 2.45 m long pipe that is open at both ends? What are the first three harmonics of this pipe when one end of the pipe is closed? Assume the speed of sound in air is 345. m/s. What is the fundamental frequency of a 0.20 m long organ pipe that is closed at one end, when the speed of sound in the pipe is 352. m/s? A flute is essentially a pipe open at both ends. The length of a flute is approximately 66.0 cm. What are the first three harmonics of a flute when all keys are closed, making the vibrating air column approximately equal to the length of the flute? The speed of sound in the flute is 340. m/s.

23. Timbre Timbre is the musical quality of a tone resulting from the combination of harmonics present at different intensities. Differences in timbre cause clarinet to sound different from a viola even when both instruments are playing the same note at the same volume. The rich harmonics of most instruments provide a much fuller sound than that of a tuning fork.

24. Harmonics of Musical Instruments

25. Nestor Kornblum sings the melody of Amazing Grace using only the overtones (harmonics) in his voice. There are NO musical instruments or electronic effects involved. Nestor Kornblum

26. Beats When two waves of slightly different frequencies interfere, the interference pattern causes a listener hears an alternation between loudness and softness.

27. Beats

28. The variation from soft to loud and back to soft is called a beat. The frequency difference between two sounds can be found by the number of beats heard per second.