Are you taking Phys. 1240, The Physics of Sound and Music, for

credit?A) yesB) no

Welcome to PHYS 1240Sound and Music

Professor Allen Hermann

Cell Phones offClickers on

7-8 L1 Sound, Oscillations,Waves, GraphsCh.1,2,S

7-9 L2 Forces, Mass, Acceleration, Pressure, Reviewof ExponentsCh.1,2, S

7-10 L3 Restoring Forces,Energy, PowerCh.1,2,S

7-11 L4 Oscillations and Waves Revisited, Interference, Waves on a StringCh.2,4,S

7-14 L5 Sound Waves, Frequency, Pitch, Tone Quality and HarmonicsCh.2,8,S

7-15 L6 Wave Intensity, Sound Level, DecibelsCh.5

7-16 L7 The Human Ear, Threshold of HearingCh.6

7-17 L8 Musical Scales, Chords, IntervalsCh.7,19

7-18 L9 Pythagorean ScalesCh.18,S

7-21 L10 The Just Scale, The Tempered ScaleCh.18,S

7-22 L11 Modes and Non-western ScalesCh.19,S

7-23 Midterm Exam 7-24 L12 String Instruments, Harmonics, the PianoCh.3,8,10,11

7-25 L13 Vibrating Rods and Membranes, Percussion InstrumentsCh.3,9

7-28 L14 Vibrating Air Columns, Organs, FlutesCh.3,12,13

7-29 L15 Brass InstrumentsCh.3,13,S

7-30 L16 Brass Instruments continued, WoodwindsCh,3,13,S

7-31 L17 Woodwinds continued, The Human VoiceCh.3,13,14,S

8-01 L18 Auditorium and Room AcousticsCh.15

8-04 L19 Auditorium and Room Acoustics continuedCh.15

8-05 L20 Electronic Sound, Analog and Digital DevicesCh.16,S

8-06 L21 Electronic Sound continued, Sampling, CD players and MP3 compression, Ch.16,S

8-07 Review for the Final Exam

8-8 Final Exam

M T W R F

GradesMid-term exam……….25%Final exam……………...35%Homework………………30%

Class participation (clicker) ..........…….10%Total……………………….100%

Exam dates:

Wed. July 23 midtermFri. Aug.8 final

CT 1.0.1

What instrument have you played? (If you have played several, which one the most?)

a) pianob) guitarc) any other instrument with stringsd) any wind instrumente) 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

isa) faster than the initial speedb) slower than the initial speedc) the same as the initial speed

PhET simulationsyou should gain access at

phet.colorado.edugo 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 shownin the simulation. What happens

at the extreme end of its motion?

A) The pendulum speeds up.B) The pendulum comes to amomentary 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 Periodf = 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

Amplitude

time (sec)1 2

Looking at the following waveform, what is the period?

a) 1 secb) 2 secc) 1 m/sd) 2 m/se) Not enough information

0

CT 2.1.2

When the amplitude of an oscillating object is doubled, the period becomes:

a) twice as bigb) 1/2 as bigc) Stays the same d) 1/4 times as bige) Not enough information to decide

When the frequency is doubled, the period becomes…

Pulses and Waves

Phet Wave on a StringPulse propagation

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) (no motion)E) (circular path)

CT 1.3.3x

PhET Wave on a StringPeriodic Oscillations or

Vibrations

Wave velocity for a periodic vibration

Let the wavelength be λand the frequency of the

vibration be f.The wave velocity v is just

V=λ/T, or

V= λf

The wavelength, λ, is 10 m. What is the speed of this wave?

a) 1 m/sb) 7 m/sc) 10 m/sd) 15 m/se) None of the above/not enough info?

CT 2.1.10

1Time (sec)

Amplitude

0

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).

m/Tv