Sound. Acoustics is the study of sound. All sounds are waves produced by vibrating objects - tuning forks, vocal chords, reeds, lips, columns of air, strings, cricket legs Demo – tuning forks - water. Sound. Sound Waves. Sound is a longitudinal wave with compressions and rarefactions.
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0.6 m/s per oC
Sound = 343 m/s
Light = 300, 000, 000 m/s
Notice that light travels much faster.
Sequence of vibrations from the source
A change in frequency (pitch) of sound due to the motion of the source or the receiver
A tuning fork with a frequency of 392 Hz is found to cause resonance in an air column spaced by 44.3 cm. the air temperature is 27oC. Find the velocity of sound in air at that temperature.
Terminology – specifically for vibrating air columns.(pipes)
Fundamental frequency – (first harmonic) -
the frequency of the longest standing sound wave that can form in a pipe.
Second harmonic – two times the frequency of the longest standing sound wave that can form in a pipe.
Third harmonic – three times the frequency of the longest standing sound wave that can form in a pipe.
Beats occur when two waves of slightly different frequencies are superimposed. A pulsating variation in loudness is heard.
Waves on a string –
the necessary condition for standing waves on a string, is that a node exist at either end.
Example: One of the harmonics on a string 1.3 m long has a frequency of 15.6 Hz. The next higher harmonic has a frequency of 23.4Hz. Find (a) the fundamental frequency, and (b) the speed of the waves on this string.