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## Waves and Sound

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### Waves and Sound Honors Physics Chapter 14 – PowerPoint PPT presentation

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Title: Waves and Sound

1
Waves and Sound
• Honors Physics
• Chapter 14

2
Definition of a wave
• A disturbance that propagates from 1 place to
another.
• Characterized by a large transfer of energy
without a large transfer of medium

3
Types of waves
• Mechanical waves require a medium (air, water,
ropes) to travel
• Electromagnetic waves do not require a medium to
• Matter waves produced by electrons and particles

4
Mechanical Waves
• Transverse the displacement of the individual
particles is perpendicular to the direction of
propagation.

5
Mechanical Waves
• Longitudinal The displacement of the individual
particles is parallel to the direction of
propagation.

6
Mechanical Waves
• Surface waves the displacement of individual
particles is circular (result of both transverse
and longitudinal motion)

7
Waves in motion
• Longitudinal and Transverse Wave Motion

8
Properties of waves
1. Amplitude (A) the maximum displacement from
equilibrium position, measured in meters.
2. Wavelength ( ?) the distance between 2 particles
that are in phase with each other, measured in
meters.

9
10
Properties of waves
• 3. Frequency (f) number of complete waves that
pass a point in one second, measured in 1/seconds
or Hertz (Hz)
• 4. Period (T) the time it takes for one complete
wave to pass a given point, measured in seconds.

11
Properties of waves
• Velocity of propagation (v) horizontal speed of
a point on a wave as it propagates, measured in
m/s.

12
Relationships/equations
• T 1/ f
• or f 1/T
• v f ?

13
Phase
• In-phase when waves are synchronized (crest
meets crest)
• Out-of-phase waves are not synchronized
• Opposite phase (180º out-of-phase) crest meets
trough

14
Reflections
• Fixed End
• Explanation
• Animation
• Open End
• Explanation
• Animation
• Between different mediums scroll down (What do
you notice about the phases? Transmitted?
Reflected?)

15
Principle of Superposition
• Occurs when two waves travel through the same
medium at the same time.
• Each wave affects the medium independently.
• The displacement of the medium is the algebraic
sum of the displacements.
• Animation

16
Interference
• Constructive occurs when wave displacements are
in the same direction (in-phase)
• Destructive occurs when wave displacement are in
different directions (out-of-phase)
• Animation(try at home)

17
What is Sound?
• Longitudinal
• Rarefaction low air pressure
• Compression high air pressure
• module (sources of sound)

18
Speed of sound
• Depends on
• Temperature
• V air 331m/s (0.6 m/s/ºC)T
• Density/kind of medium
• Gases ltliquidsltsolids
• Chart of speeds

19
Speed of sound
20
Pitch
• How we perceive variations in frequency
• Audible range 20-20,000 Hz (listen)
• Infrasonic vs. ultrasonic
• Most sensitive to 1,000 to 5,000Hz
• Loudness can distort our perception of pitch
(listen tape)
• Module (pitch)

21
Doppler Effect
• Variation in the frequency of sound due to the
relative motion of the sound source or the
listener.
• Animation1 (try at home)
• Picture of a sonic boom
• Video of sonic boom
• mythbuster

22
Doppler Effect Results
• As an moving sound source approaches a listener
the frequency (pitch) increase.
• As a moving sound source passes by a listener the
frequency (pitch) decreases.
• Same effect if sound source is stationary and
listener is moving.

23
Calculating Frequency change
• f f (v vR / v vs)
• f new frequency
• f original frequency of source sound
• v velocity of sound
• vs velocity of source

24
Loudness
• How we perceive variations in amplitude and
intensity.
• Module (loundness)
• In general, sound waves of higher intensity sound
louder but we are not equally sensitive to all
frequencies.

25
Sound Intensity
• The amount of energy that passes through a given
area in a given time.
• IP/A
• Ppower (watts)
• A area (m2)
• I intensity (W / m2)
• Directly proportional to the square of the
amplitude.
• Inversely proportional to the square of the
distance from the source.

26
Relative Intensity
• Logarithmic scale used to indicate the intensity
level of a sound.
• Measured in decibels or dB
• ß 10 log (I / Io)
• Io 110-12 W/m2 (intensity of the faintest sound
that can be heard)
• I intensity of sound in W/m2

27
How loud is a decibel?
• Threshold of hearing( Io ) 0dB (air pressure
210-5 Pa)
• Threshold of pain 120 dB (air pressure 20 Pa)
• We perceive a 10 dB increase as twice as loud.
• Every 20 decibels air pressure increases 10 times
• Table of sound levels

28
Resonance
• Causing the vibration of an object by the
influence of another vibrating body.
• Must match the natural frequency of vibration of
the object
• Whole-number multiple of the natural frequency
work too.
• Breaking a glass with resonance

29
Standing waves
• Caused by the interference of reflected waves
with incident waves from the source.
• Nodes pts of no displacement
• Antinodes pts of maximum displacement
• Applet (try at home)

30
Vibrating Columns of Air
• Column will emit a sound when the air inside
achieves resonance.
• DEMO (cardboard moose call)
• Frequency of vibration depend on
• Length of column
• Type of column
• Open end
• Closed end

31
Fundamentals and Harmonics
• Fundamental Frequency lowest frequency of
vibration
• Harmonics whole number multiples of the
fundamental
• Note the fundamental frequency is the 1st
harmonic.
• Animation

32
Calculations for closed pipe
• Fundamental frequency
• f1 v /4L (Llength of air column)
• Harmonics
• fn nf1 (n1,3,5,)
• ? 4L/n
• Note only ODD harmonics are produced
• Animation

33
Closed (at one end) pipe
• The standing wave created has
• Node at closed-end
• Antinode at open-end

A
N
34
Open pipe
• The standing wave created has
• Antinode at both ends

A
A
35
Calculations for open pipe
• Fundamental frequency
• f1 v /2L (Llength of air column)
• Harmonics
• fn nf1 (n1,2,3,)
• ? 2L/n
• Note ALL harmonics are produced
• animation

36
Frequency
• Light
• Sound (listen)
• BACK