1. Sound

2. Characteristics Loudness --> Amplitude Pitch -->frequency

3. Wave Formulas

4. Sound Waves Longitudinal or compressional waves Require a medium Travel fastest in solids, then liquids, and slowest in gases

5. Range of Hearing in Humans Average range is 20 – 20,000 Hz Infrasonic - frequencies below 20 Hz or below the range of hearing for humans Ultrasonic - frequencies above 20,000 Hz or above range of hearing for humans

6. Speed of Sound in Air The speed of sound in air changes with temperature. The speed at 0 o C is 331m/s for dry air It increases by 0.6 m/s for each degree Celsius above zero.

7. Echoes An echo is a reflected sound wave An echo travels to a barrier and then reflects back Note: So time is usually given there and back but distance is given only one way (so either ½ the time or double the distance).

8. Doppler Effect f ' = apparent frequency (detected freq), Hz f = frequency of source (emitted freq), Hz v = velocity of sound in air, m/s v s = velocity of source, m/s v o = velocity of observer or detector, m/s Note: Use if v is not given.

9. Doppler - continued Use if the observer and source are getting closer together Use if the observer and source are getting farther apart

10. Remember units! Frequency -- Hertz (cycles/sec) Period -- seconds Wavelength -- meters Wave speed -- m/s Sound Intensity -- W/m 2 Relative sound intensity -- decibels (dB)

11. Beats Beats occur due to interference patterns between sound waves of slightly different frequencies. Hear alternating loud and soft sounds. Humans can only hear beat frequencies of 7 Hz or less. Δf = beat frequency, beats/sec or Hz f 1 = frequency of one sound, Hz f 2 = frequency of another sound, Hz

12. Resonance A condition that exists when the frequency of a force applied to an object matches the natural frequency of vibration of the object. The object will then begin to vibrate with sympathetic vibrations. An extreme example of resonance is the collapse of the Tacoma Narrows Bridge.