1Physics 1240 1/19/06 Today: Periodic vibrations and pitch Next time: Waveforms and digital sound Last time The physical nature of sound can be categorized into four basic processes: Generation (source), Propagation (waves), Reception/Perception (hearing), Processing (mainly digital electronics) Speed of sound: v = 344 m/s Super TA: Jeff Merkel [email protected] Cell: 303-359-0737, Studio: 303-298-1386 Discussion Session: TO BE ANNOUNCED2Outline - Periodicity and pitch - Simple harmonic motion - Frequency and pitch - Vibrations versus Waves3Only a vibration that repeats itself at regular intervals produces the sensation of a distinct pitch pitch – the sensation of how high or low a steady tone sounds steady tone – a sound that is held steady that produces the sensation of a musical note4CT 1.3 Which object might exhibit periodic motion? A) a lump of clay B) a gong C) a guitar string on a guitar5CT 1.4 What object probably does not exhibit periodic motion? (assume the instrument plays only one note) A) piano B) bass guitar C) drum D) oboe E) acoustic guitar6Periodic motion -- repeats itself at regular intervals f = frequency = 1 / period P = period -- units of second frequency -- cycles/second -- 1/(second) - Hertz (Hz) A = Amplitude - how large the vibration is78T 1.5 A tuning fork has periodic motion that repeats itself every 0.001 seconds (1 millisecond), what is the frequency? A) 10 Hz B) 100 Hz C) 1000 Hz D) 10,000 Hz9Simple Harmonic Motion = Simple Periodic Motion = Sinusoidal Motion This is a sine waveform: (note: I was careful not to say “sine wave”)10QT1.6 What object is an example of simple harmonic motion? A) pendulum at large amplitudes B) mass on a spring at small amplitudes C) a tuning fork D) none of the above11 Physics Jargon (we need it to be precise) “Oscillator” -- something that exhibits periodic motion “Oscillation” -- the periodic motion itself “Displacement” -- distance the motion travels from zero vibration -- oscillation -- waveform12Frequency (physical) determines pitch (sensation). very exact! Higher pitch = higher frequency Lower pitch = lower frequency13QT1.7 If we double the period of a musical vibration what would happen to the pitch? A) It would go up by a factor of 4 B) It would go up by a factor of 2 C) the pitch would not change D) the pitch would go down14vibration (oscillation, waveform) -- a function of time only wave -- a function of both position and time15 QT1.8 What object is a good example of wave motion? A) pendulum at large amplitudes B) mass on a spring at small amplitudes C) a tuning fork D) none of the
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