Sound and sound waves
sound waves are longitudinal waves (also called compression or pressure waves)
get vibrations from source of sound (eg. loudspeaker, vocal chords)
individual molecules vibrate
...
Sound and sound waves
sound waves are longitudinal waves (also called compression or pressure waves)
get vibrations from source of sound (eg. loudspeaker, vocal chords)
individual molecules vibrate back and forth (horizontal motion) about (fixed) equilibrium position
get a travelling wave moving through gas, liquid, or solid (needs a “medium”)
frequency
of the wave is determined by the source
PHYS117
the wavelength
speed
is the distance from high P to high P (or low P to low P) in the direction of travel
of the wave is determined by the medium
Hearing by the auditory system:
vibration of air is carried to the eardrum
eardrum vibrates at the frequency of the sound wave
vibrations are transmitted to the inner ear where they are converted to electrical impulses and transmitted to the brain
the brain processes the electrical impulses as sound
continued exposure to high amplitude pressure fluctuations
damages inner ear and nerve pathways to brain
vibrating guitar string (transverse disturbance) introduces
vibrational motion to surrounding air molecules
vibrational motion in air produces a longitudinal (travelling)
sound wave
get sound wave at same frequency as wave on string
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Frequency is the number of cycles per second (Hz).
A sound with a single frequency is called a pure tone.
(eg. sound generated by a tuning fork)
The pure tone sound wave consists of air pressure fluctuations
which can be described by a sine wave.
The brain interprets the frequency of the sound wave in terms of the subjective quality called pitch.
high frequency sound = high pitch
low frequency sound = low pitch
ideally humans hear all frequencies from 20 Hz to 20,000 Hz
Loudness (as interpreted by the brain) depends on the amplitude
(related to the energy) of the sound wave. >
PHYS117
3-1
The use of the term "sound waves" in air is meant to describe (choose the “best” answer):
A. the position of air molecules.
B. the velocity of air molecules.
the pressure variations in air.
D. the displacement of air molecules.
E. none of the above
...........................................CONTINUED...........................................
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