Transcript Bell Quiz - 2nd - Steinbrenner High School

Mechanical Wave
A disturbance which
propagates through a
medium with little or no net
displacement of the
particles of the medium.
Parts of a Wave
: wavelength
3
equilibrium
2
-3
y(m)
crest
A: amplitude
4
trough
6
x(m)
Speed of a wave

Speed of a wave

Period of a wave

Wave types: transverse
A transverse wave is a wave in
which particles of the medium
move in a direction
perpendicular to the direction
which the wave moves.
Example: waves on a string
Wave types: transverse
Wave types: longitudinal
A longitudinal wave is a wave in which
particles of the medium move in a
direction parallel to the direction which
the wave moves.
Longitudinal waves are also called
compression waves.
Example: sound
Wave types: longitudinal
Longitudinal vs Transverse
Other Wave Types
Earthquakes:
combination
Ocean waves: surface
Light: electromagnetic
Reflection of waves
• Occurs when a wave strikes a
medium boundary and
“bounces back” into original
medium.
• Completely reflected waves
have the same energy and
speed as original wave.
Reflection of waves

Fixed-end reflection: wave reflects
with inverted phase. This occurs
when reflecting medium has greater
density.
Reflection of waves

Open-end reflection: wave reflects
with same phase. This occurs when
reflecting medium has lesser density.
Refraction of waves
• Transmission of wave from
one medium to another.
• Refracted waves may change
speed and wavelength.
• Refracted waves do not
change frequency.
Principle of Superposition
When two or more waves pass a
particular point in a medium
simultaneously, the resulting
displacement at that point in the medium
is the sum of the displacements due to
each individual wave.
 The waves interfere with each other.

Types of interference.


If the waves are “in phase”, that is crests
and troughs are aligned, the amplitude is
increased. This is called constructive
interference.
If the waves are “out of phase”, that is
crests and troughs are completely
misaligned, the amplitude is decreased and
can even be zero. This is called destructive
interference.
Constructive Interference
crests aligned with crest
waves are
“in phase”
Destructive Interference
crests aligned with troughs
waves are
“out of
phase”
Sound is a longitudinal wave
Sounds in the Real World
Because of superposition and
interference, real world waveforms
may not appear to be pure sine or
cosine functions. That is because
most real world sounds are
composed of multiple frequencies.
Making Waves
A disturbance which
propagates through a
medium with little or no net
displacement of the
particles of the medium.
Standing Wave
A standing wave is a wave which is
reflected back and forth between
fixed ends (of a string or pipe, for
example).
 Reflection may be fixed or openended.
 Superposition of the wave upon itself
results in constructive interference
and an enhanced wave.

String Thing
String Thing
String Thing 1
String Thing 1.5
String Thing 2
Fixed-end standing waves
(violin string)
L
First Overtone
Second harmonic
L=2
Open-end standing waves
(organ pipes)
L
First Overtone
Second harmonic
L=2
Not on AP Formula Sheet;
however, need to know!
 Memorize:
Stringed
Instruments
or OpenPipe
Equation

Closed at One End (some organ
pipes)-How Odd Is That?
L
Not on AP Formula Sheet;
however, need to know!
 Memorize:
Closed-Pipe
Equation
 How Odd is
That?

Doppler Effect
 The
Doppler Effect is the raising
or lowering of the perceived pitch
of a sound based on the relative
motion of the observer and the
source of the sound.
Doppler Effect
When an ambulance is racing toward
you, the sound of its siren appears to
be higher in pitch.
 When the ambulance is racing away
from you, the sound of its siren appears
to be lower in pitch.

Doppler Effect
 The
Doppler Effect is the raising
or lowering of the perceived pitch
of a sound based on the relative
motion of the observer and the
source of the sound.
Doppler Effect
When an ambulance is racing toward
you, the sound of its siren appears to
be higher in pitch.
 When the ambulance is racing away
from you, the sound of its siren appears
to be lower in pitch.

A final word about “pitch”
 Pitch
rises when frequency
rises and the sound is
“higher”.
 Pitch is lowered when the
frequency is lowered and the
sound is “lower”.
Beats
The characteristic loud-soft pattern
that characterizes two nearly (but
not exactly) matched frequencies.
 Musicians call this “being out of tune”

What word best describes this
to physicists?
Amplitude
Answer: beats
What word best describes this
to musicians?
Amplitude
Answer: bad intonation
(being out of tune)
Resonance
Occurs when a vibration
from one oscillator occurs
at a natural frequency for
another oscillator.
The first oscillator will
cause the second to
vibrate.
Tacoma Bridge Incident

Resonance-Play Video