W2-3-notes

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 PHYS117 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 ........................................CONTINUEED.................................................