Are you taking Phys. 1240, The
Physics of Sound and Music, for
credit?
A) yes
B) no
Welcome to PHYS 1240
Sound and Music
Professor Allen Hermann
Cell Phones off
Clickers on
M
T
W
7-8 L1 Sound,
Oscillations,
Waves, Graphs
Ch.1,2,S
R
F
7-9 L2 Forces, Mass,
Acceleration, Pressure,
Review
of Exponents
Ch.1,2, S
7-14 L5 Sound
7-15 L6 Wave
7-16 L7 The Human
Waves, Frequency, Intensity, Sound Level, Ear, Threshold of
Pitch, Tone Quality Decibels
Hearing
and Harmonics
Ch.5
Ch.6
Ch.2,8,S
7-21 L10 The Just 7-22 L11 Modes and
7-23 Midterm Exam
Scale, The
Non-western Scales
Tempered Scale
Ch.19,S
Ch.18,S
7-10 L3 Restoring
Forces,
Energy, Power
Ch.1,2,S
7-28 L14 Vibrating 7-29 L15 Brass
Air Columns,
Instruments
Organs, Flutes
Ch.3,13,S
Ch.3,12,13
7-31 L17 Woodwinds 8-01 L18 Auditorium
continued, The Human and Room Acoustics
Voice
Ch.15
Ch.3,13,14,S
8-04 L19
Auditorium and
Room Acoustics
continued
Ch.15
8-05 L20 Electronic
Sound, Analog and
Digital Devices
Ch.16,S
7-30 L16 Brass
Instruments
continued,
Woodwinds
Ch,3,13,S
8-06 L21 Electronic
Sound continued,
Sampling, CD players
and MP3 compression,
Ch.16,S
7-11 L4 Oscillations
and Waves Revisited,
Interference,
Waves on a String
Ch.2,4,S
7-17 L8 Musical Scales, 7-18 L9 Pythagorean
Chords, Intervals
Scales
Ch.7,19
Ch.18,S
7-24 L12 String
Instruments,
Harmonics, the Piano
Ch.3,8,10,11
8-07 Review for the
Final Exam
7-25 L13 Vibrating
Rods and Membranes,
Percussion
Instruments
Ch.3,9
8-8 Final Exam
Grades
Mid-term exam……….25%
Final exam……………...35%
Homework………………30%
Class participation (clicker)
..........…….10%
Total……………………….100%
Exam dates:
Wed. July 23 midterm
Fri. Aug.8 final
CT 1.0.1
What instrument have you played? (If you have played several, which
one the most?)
a)
b)
c)
d)
e)
piano
guitar
any other instrument with strings
any wind instrument
never played any instrument
What is sound?
Sound is produced by periodic vibrations, but we need a
medium as well for the sound to propagate. Sound is different
from light in that it cannot travel in empty space. So an explosion
of a distant star would never be heard by us on earth.
Sound travels as mechanical waves, through solids liquids and
gases.
So to understand sound, we must understand periodic vibrations
or oscillations (the source of sound), the movement of the
disturbance which these vibrations cause through a material
medium (sound wave), and the reception of this disturbance by,
e.g. the ear.
Graphs
The slope is the speed
(discuss the term “velocity”).
In the last slide the initial slope
corresponds to about 180 m
traversed in about 3 minutes (180
sec), or the initial speed is about
180m/180 sec= 1 m/s
In the period between second 6
and second 9, the student’s speed
is
a) faster than the initial speed
b) slower than the initial speed
c) the same as the initial speed
PhET simulations
you should gain access at
phet.colorado.edu
go to Play with SIMS
we will do The Moving Man
To learn about Periodic
Vibrations or
Oscillations, we must
first learn about Forces
A little about Vectors
The bigger the weight (force on the
spring), the more the spring extends
and the more the spring “pulls back”,
i.e. the greater the restoring force.
We can write the restoring force Fr is
proportional to the extension x,
Fr=-kx
PhET Masses and Springs
PhET Pendulum Lab
Consider the pendulum shown
in the simulation. What happens
at the extreme end of its motion?
A) The pendulum speeds up.
B) The pendulum comes to a
momentary full stop.
C) The pendulum reaches its
maximum frequency.
D) The pendulum reaches its
minimum angle with respect to
a vertical line.
E) The pendulum’s weight
increases.
Simple Harmonic Motion
• Position x vs. time t
• Definition of period T
• Definition of amplitude A
SHM Systems
Let the period be T (in
seconds).
The number of times the
vibrating source executes SHM
in one second (i.e. the
frequency, f, units of Hz)) is
1/T.
For example, if T is 0.1 s, f is
just 1/0.1=10 Hz
Frequency and Period
f = 1/T or T = 1/f or f T =1
T period, in seconds (s)
f = frequency in Hertz (Hz)
Metric prefixes:
centi- (c), milli- (m), micro- (m)
kilo- (k), mega- (M)
CT 2.1.8
Looking at the following waveform, what is the period?
Amplitude
0
a) 1 sec
b) 2 sec
c) 1 m/s
d) 2 m/s
e) Not enough information
1
2
time (sec)
CT 2.1.2
When the amplitude of an oscillating object is doubled, the period
becomes:
a) twice as big
b) 1/2 as big
c) Stays the same
d) 1/4 times as big
e) Not enough information to decide
When the frequency is doubled,
the period becomes…
Pulses and Waves
Phet Wave on a String
Pulse propagation
CT 1.3.3x
I grab the left end of a LONG string and wiggle it up and
down. There is a purple painted spot somewhere on the string.
What choice below best shows the motion of the purple
spot?
A)
(up and down)
B)
(pushed steadily to the right)
C)
(left and right)
D)
E)
(no motion)
(circular path)
PhET Wave on a String
Periodic Oscillations or
Vibrations
Wave velocity for a
periodic vibration
Let the wavelength be λ
and the frequency of the
vibration be f.
The wave velocity v is just
V=λ/T, or
V= λf
CT 2.1.10
The wavelength, λ, is 10 m. What is the
speed of this wave?
Amplitude
0
a)
b)
c)
d)
e)
Time (sec)
1
1 m/s
7 m/s
10 m/s
15 m/s
None of the above/not enough info?
What determines the velocity of a
transverse pulse or wave on a
string (v=λf simply constrains f and
λ) ?
The velocity is determined by the
tension T ( a force in N) applied to
the string, and the mass per unit
length μ ( in kg/m).
v T /m