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- Doppler Effect: An effect in which the observed frequency is different than the frequency being emitted by a source and is caused by a relative
motion between the observer and source of the sound.
- Reflection - waves “bounce” off of barriers - Refraction - when the speed of a wave changes for some reason. Often, but not always, refraction will cause a wave to change direction. Refraction
can happen when waves go from one medium to another or if the properties of a medium change.
- Diffraction - the ability of waves to bend around obstacles
- Interference - same ideas as earlier in the chapter…
!
f = f
v ± v
o
v ± v
s
$
%
%
&
'
(
(
- Resonance - an effect when a system is driven at (or near) a natural frequency. The resulting amplitude of the vibration
dramatically increases.
There are two “types” of resonances, narrow and broad. The Q-factor is the man way to categorize resonances.
The smaller the linewidth ( ∆f ) the sharper the resonance or the higher the Q-factor. Basically the higher the Q-factor, the
closer you have to get to resonance to see an effect. While resonance is an important acoustical phenomenon, resonant
effects are not always desired.
This is how the book arrives at the generalized formula for the frequencies of modes of vibration (for a string fixed at both
ends ).
here n = 1, 2, 3,… and fn will be the frequency of the n
th
harmonic (the 1
st
harmonic is usually called the fundamental).
f
n
n
2 L
T
μ
!
Q =
f
o
" f
- Pipe open at one end - the boundary conditions require an antinode at the open end and a node at the closed end. The resonant
frequencies are given by:
Note: only the odd harmonics are present (or audible) in this system
- Metallic rods with both ends free - the boundary conditions require antinodes at both ends. The resonant frequencies are given by:
n = 1, 3, 5,…
!
f
n
nv
4 L
n = 1, 2, 3,…
f
n
=
n
2 L
E
"
- Sympathetic vibrations - the vibration of one object due to the vibration of another object. Examples of this include the
tuning fork and speakers.
- Logarithms - y is the base , x is the power or exponent and N is the number generated by taking the base to the power
log
y
N = x
Review - Chapter 5
