Sound and Waves
Unit 4
Workshop Overview
Waves and Sound: Unit 4
 Inv. 11.1: Harmonic Motion (pendulum)
 Inv. 12.2: Waves in Motion (wave tray)
 Inv. 12.3: Natural Frequency and
Resonance (waves on a string)
 Selected parts of investigations in Chapter
13 – Sound.
Investigation 11.1
Harmonic Motion
Harmonic Motion
Motion that repeats itself over and over
Examples of harmonic motion
 Rotation and revolution of Earth
 Back and forth motion of a swing
 Turning bicycle wheel
Oscillator
Objects or systems that exhibit harmonic
motion
Examples of oscillators
 Earth
 Vibrating guitar string or tuning fork
 Quartz crystal timekeeper in watch or
computer
 Pendulum!
Pendulum
 Excellent device for learning about
oscillators and harmonic motion
 Apply basic pendulum concepts to more
sophisticated behavior, such as waves and
sound.
Four New Ideas
 Speed, velocity, and acceleration are great
ways to describe linear motion, but not
harmonic motion.
 Need 4 new ideas:




Cycle
Period
Frequency
amplitude
Experimenting with the Pendulum:
Investigation 11.1
Set up the pendulum
Setting up the Photogate
Using the Timer with the Pendulum
IMPORTANT INFO
 When you use the timer in period mode,
the period represents the time between
breaks of the photogate beam. Therefore,
since the pendulum bob breaks the beam
twice in one complete cycle, you need to
multiply the reading on the timer by TWO
to get the time for one cycle (period).
MORE IMPORTANT INFO
 The “reset” button works differently in period
mode.


When you hit reset once, it freezes the display.
Hit reset again, and you will reset the display.
 After a reset, you must let the bob swing through
the photogate at least twice before another
reading will show up on the timer.
Let’s investigate!
 Watch the pendulum swing through the
photogate. Play with this awhile until you
get the bob to swing through without hitting
the gate.
 Use leveling feet to level your stand
 Pull string out to the end of the slot so the
bob doesn’t hit the pole
 Cycle: smallest complete unit of motion
that repeats.
 Period: the time it takes to compete one
cycle
 Amplitude: maximum displacement the
oscillator moves away from average or
resting position
 Frequency: number of cycles an oscillator
completes per unit of time (cycles per sec).
About the pendulum…
 Demonstrate one complete CYCLE of the
pendulum.
 How will you measure the PERIOD of the
pendulum? (Period is more useful than
frequency when studying slow oscillators).
 How will you measure the AMPLITUDE of
the pendulum?
What variables affect the period
of the pendulum?
 You can change 3 variables of a
pendulum:



Mass
Amplitude
String length
 Devise a controlled experiment (or a series
of mini experiments) to determine which
variables significantly affect the period.
Change each variable by a large amount;
3 trials is sufficient.
Hints
 Changing mass:
use the cord stop to
hold washers on the
string behind the
pendulum face:
Measure from
top of string to
bottom of
washers
Which variable significantly
affects the period of the
pendulum?
String Length
Application
 Make a 30-sec clock, accurate to within 0.5
seconds!
 interactive stopwatch

This onscreen stopwatch makes the application
activity more fun!
Investigation 12.2
Waves in Motion
Bridging the Concepts
 Waves are oscillations that TRAVEL; a
pendulum stays in one place.
 Waves carry oscillations from one place to
another
 Waves carry information from one place to
another!
How do waves move and interact?
 Fill tray with about 1 cm of colored water
 Practice making transverse waves by
using plastic wand
 Practice making circular waves by dipping
your finger in the water
How do waves interact with
boundaries and materials?
 Diffraction: how waves change shape
when passing through openings or around
obstacles
 Model how diffraction can occur in the
wave tray
 Examples of diffraction


Hearing someone through a crack in a door
Diffraction grating glasses
How do waves interact with
boundaries and materials?
 Reflection: how waves bounce off of
things
 Model how reflection can occur in the
wave tray
 Examples of reflection:


Echo
Seeing yourself in a mirror
How do waves interact with
boundaries and materials?
 Refraction: how waves can be bent when
they pass through a boundary
 refraction will be modeled in the unit on
light
 Examples of refraction:


Eyeglasses
telescopes
Investigation 12.3
Natural Frequency and
Resonance
Bridging the Concepts
 Waves usually travel, but you can make a
wave stay in one place to study it.
 Standing Wave: wave trapped in one spot
 To make standing waves, you need
boundaries to bounce or reflect the wave
back on itself


Sound: boundaries are hard surfaces
Light: boundaries could be mirrors
Standing Waves in Daily Life
 Flute: standing wave of sound inside the
instrument
 Wave pool: standing wave of water
 Laser: standing wave of light
 Guitar string: standing wave on a vibrating
string
Standing Wave on a String
 We can make standing waves and study
them by using the CPO wave generator
equipment
Basic characteristics of waves
Frequency
 “how often” (cycles/sec,
wiggles/sec, ) Hertz
Wavelength

Length of one
wave (“S” shape)
Basic characteristics of
waves
 Node
 Points where the string
does not move
 Anti-node
 Points where the string
moves the most
Common Uses for Waves
 Radio waves are used to carry
signals over large distances
 Ultrasound uses very high
frequency sound waves to make
images of the inside of the body
 Light is a wave that has different
frequencies we call colors
Set up a Wave Experiment
Change The Frequency
 Observe the string as you change
the frequency
 Describe What Happens
Patterns on the String
Standing
Wave
Patterns
OBSERVATONS
 The string vibrates
 Standing Wave patterns appear at some
frequencies
 All of these frequencies are multiples of
the lowest one that produces this effect
 The frequency multiplied by the
wavelength of each standing wave is
the same for all of the waves
Other things to try
 Measure the amplitude at different
frequencies
 Measure the frequency at which a certain
harmonic occurs for different string
tensions
RESONANCE
 A Condition where a Driving Force or push
occurs at a frequency that results in a
Standing Wave
 These Standing Waves occur at what are
called Natural Frequencies or Harmonics
 Every object, substance and material has
its own Natural Frequencies, where they
“like” to vibrate
 All Natural Frequencies are multiples of the
Fundamental
FREQUENCY x WAVELENGTH
 Each Harmonic has a different frequency and
wavelength
 Frequency x Wavelength gives the same answer
for ALL Harmonics
 Cycles/Seconds x Meters/Cycle= Meters/Second
which is a value for speed of the Wave on the
string
 If Frequency increases, Wavelength decreases and
if Frequency decreases, Wavelength increases
Chapter 13 investigation overview
Sound Waves
 How do we perceive Sound Waves?
 What do they have in common with
other kinds of waves?
 What is different about Sound Waves?
Set Up a Sound Experiment
 Disconnect the Wiggler from the Sound and
Waves Machine
 Connect Mini-Speakers to the Sound and Waves
Machine
 Switch the CPO Timer II to Sound Mode
Tuning Notes for Chords
Note Name
C
D flat
D
E flat
Frequency
264
285
297
317
E
330
F
352
G flat
380
G
396
A flat
422
A
B flat
440
475
B
495
C
528
C major
C minor
D major
Tuning Notes for Chords
Note Name
C
D flat
D
E flat
Frequency
264
297
317
330
F
352
G flat
380
G
396
A flat
422
B flat
Yes
285
E
A
C major
Yes
Yes
440
475
B
495
C
528
Optional
C minor
D major
Tuning Notes for Chords
Note Name
C
D flat
D
E flat
Frequency
264
Yes
Yes
297
317
330
F
352
G flat
380
G
396
A flat
422
B flat
C minor
285
E
A
C major
Yes
Yes
Yes
Yes
440
475
B
495
C
528
Optional
Optional
D major
Tuning Notes for Chords
Note Name
C
D flat
D
E flat
Frequency
264
Yes
Yes
297
D major
Yes
317
330
F
352
G flat
380
G
396
A flat
422
B flat
C minor
285
E
A
C major
Yes
Yes
Yes
Yes
Yes
440
Yes
475
B
495
C
528
Optional
Optional
Sound and Music - Chords
 Different notes have different
frequencies
 Chords are combinations of different
notes with specific mathematical
relationships
 Different relationships of the notes will
produce chords with very different
“moods” or “feel”
The Musical Scale
 Mathematical Relationships in the form of
Ratios
1 9/8 5/4 4/3 3/2 5/3 15/8 2
DO RE MI FA SO LA TI DO
264 297 330 352 396 440 495 528
C D E
F
G
A
B
C
Different frequencies for Middle C
 Click on the link below for a brief
discussion of why the frequency of middle
C can differ.
 Frequency of Middle C
Sound and Music - Beats
 Small Difference in
Frequency
 Product of Interference
Note Name
Key Color Frequency
C
528
B
495
B flat
A
475
440
A flat
422
G
396
G flat
380
F
352
E
330
E flat
D
D flat
C
317
297
285
264
Musical Instruments
 Musical instruments play different
notes
 Frequencies are controlled by
altering wavelength
 Vibrating materials like strings or
reeds cause chunks or columns of
air to vibrate
Musical Instruments
 Natural Frequencies/Harmonics cause
amplification through Resonance
 Instruments can be amplified this way
and/or electronically
 The vibrating element vibrates at ALL its
Harmonics, not just the Fundamental.
 The combination of these frequencies
give an instrument its particular sound.
Questions/Answers