MUSIC• Musical Tone-
Pleasing sounds that have periodic wave patterns.
• Quality of sound- distinguishes identical notes from different instruments. http://
www.animations.physics.unsw.edu.au/jw/sound-pitch-loudness-timbre.htm
Beats- the change in sound intensity due to the interference of sound.
Beat Frequency- the number of maximum intensity points per second.
2 beats
Ex. A sound with a frequency of 400Hz interferes with a second sound. If this produces 20 beats in 5.0 seconds, what is the frequency of the second sound?
BF= 20beats/ 5 sec = 4 beats/sec
4 beats/sec = | 400Hz- f2 | = 396Hz or 404Hz
BF = # beats or BF = | f1 – f2 | second
MODES OF VIBRATION
Fundamental mode, lowest pitch. λ = 2L
First overtone, second harmonic, λ = L
Second overtone, 3 rd harmonic, λ = 2/3L
Third overtone, 4th harmonic, λ = 1/2L
HARMONICS
Whole number multiples of the fundamental frequency. Doubling the frequency will raise the pitch one octave (8 notes)
LAWS OF STRINGS
Law of Length: As the length of a string increases, frequency and pitch decreases.
Law of Diameter: As the diameter of a string increases, frequency decreases.
Law of Tension: As the tension on a string increases, frequency and pitch increases.
Law of Density: If a more dense string is used, the frequency and pitch decreases.
Wavelength depends of the length and diameter of the resonating pipe.
λ = 2( L + 0.8d) L- length (m)
d- diameter (m)
Ex: An open plastic pipe will resonate at its lowest frequency when a tuning fork is held over it.
A) If the pipe has a length of 60cm and a diameter of 4.0cm what is the wavelength?
λ = 2( L + 0.8d)
λ = 2(0.6m + 0.8(0.04m)
λ = 1.264m
B) If the sound produced has a speed of 342m/s, what is its frequency?
(Lowest frequency is the 1st harmonic.)
f1 = v/2L
f1 = 342m/s / (2 x 0.6m)
f1 = 285 Hz
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