Review Section I
Picture of a Transverse Wave WAVE DESCRIPTION Picture of a Transverse Wave Crest Wavelength l A - Amplitude A Trough
Wave Types Longitudinal Waves Transverse Waves
Fundamentals Wavelength (l) Period (T) Frequency (f = 1/T) Amplitude (A) Speed (v = distance/time) = lf
Oscillation Categories Natural Frequency The set of frequencies an object emits when struck Forced Vibration Causing a vibration at a frequency other than a natural frequency Resonance Causing a vibration at a natural frequency Amplitude increases
Waveform – amplitude vs. time Impulsive Sound Waveform – amplitude vs. time
Impulsive Sound Halving Time Method of striking makes a difference Hard vs. soft hammer The position of striking makes a difference Tuning fork sounds difference when struck at the end compared to striking at the center
Superposition
Decaying Sound Frequency (f) Initial Amplitude (Amax) Halving Time (T½)
Damped Sinusoidal Motion By experiment we get Or, in symbols
Halving Time Notice – the larger the mass, the slower it vibrates and the longer it takes for the oscillations to die away
VIBRATION OF A PENDULUM What does the period (T) depend upon? Length of the pendulum (l). Acceleration due to gravity (g). Period does not depend upon the bob mass.
Not simply related to the fundamental Frequencies for bars Not simply related to the fundamental Observed P/P = 1.000 Q/P = 2.68 R/P = 3.73 S/P = 5.25 P = 1046.5 Hz Q = 2810 Hz R = 3906 Hz S = 5494 Hz
Clock Chimes and Bells Trained listeners often disagree as to the pitch assignment Due to the fact that several identifiable harmonic series may be present
Harmonics 1st 2nd Sum
Plucked strings The frequencies are very nearly whole numbers fn = nf1
Assigned Pitch Our ears assign pitches based on any whole number sequences they can find. Assigned pitch is the lowest frequency that gives harmonics
Bell Harmonics
Model with Many Masses Normal Modes ½ wavelength 1 wavelength 1½ wavelengths 2 wavelengths Lowest mode shows ½-wavelength Each mode is ½-wavelength different from its neighbors