2. Chapter 2 Impulsive Sounds, Alone and in Sequence

3. Picture of a Transverse Wave Wavelength Amplitude A Crest Trough WAVE DESCRIPTION

4. Transverse and Longitudinal Waves Wave Motion Click on the phrase above and then select either transverse or longitudinal waves  Sound is a longitudinal wave disturbance  Wavelength is the distance between compression.

5. Sound is a Longitudinal Wave The tuning fork moves air molecules back and forth in the direction the sound wave travels

6. - meters or feet Distance between adjacent crests in a transverse wave Distance between compressions in a longitudinal wave Distance a wave travels during one vibration Units Wavelength ( )

7. Time required to make one vibration. Time required to generate one wave. Time required for the wave to travel one wavelength. Period (  )

8. The number of vibrations per unit of time made by the vibrating source. Units - cycles per second 1/s Hertz (Hz) Frequency (f)

9. What is the frequency of the second hand of a clock? Frequency = 1cycle/60 secPeriod = 60 sec What is the frequency of US Presidential elections? Frequency = 1 election/4 yrsPeriod = 4 yrs Examples of Frequency

10. In symbolic formor

11. Demo - Drop Different Sounding Objects Rap on Table Finger Snap Tuning Fork NATURAL FREQUENCY Objects have natural frequencies at which they vibrate. The natural frequency depends on elasticity and shape.

12. A Selection of Natural Frequencies

13. Resonance occurs when successive impulses are applied to a vibrating object at the object’s natural frequency. Result - increased amplitude Examples: Swinging Marching on a bridge RESONANCE Tacoma Narrows Bridge

14. 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 FORCED VIBRATIONS

15. Equally Tempered Scale In most acoustics texts the octaves are numbered from the left side of the piano keyboard. The note labeled C 4 is middle C.

16. Octaves If the note has the same pitch name, then the frequency is related by a power of 2.  C 4 = 256 HzA 4 = 440 Hz  C 5 = 512 HzA 5 = 880 Hz

17. Repetition Rates Consider a drummer playing with his left hand (o) and his right hand (x). He might play -------o-------o-------o-------o-------o-------o-------o-------o Next he plays a flam -------o-x-----o-x-----o-x-----o-x-----o-x-----o-x-----o-x----- Or, -------o---x----o---x----o---x----o---x----o---x----o---x----o

18. Repetition Rates We would have no trouble identifying this as the same frequency as the original But put the beat of the other hand at the exact midpoint and the listener hears twice the repetition rate.

19. Electronic Experiment Frequency Generator Delay D Shaper 2 Shaper 1 Sum Audio Ampl.