Wave Motion

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Transcript Wave Motion

Today’s Agenda: Waves Day 2
Do Now:
1. Come up with at least 3 different
kind of waves.
2. Turn to your partner and
together think of two more types of
waves.
Schedule:
1. Do Now
2. Wave Activity
3. Groups present
4. Lecture on Wave Properties
5. Standing wave generator demo
**Homework: Conceptual Physics
Worksheet
Objectives:
1. The student will know the units of period, wavelength, frequency, and wave velocity.
2. The student will be able to classify wave types.
3. The student will be able to identify wave characteristics.
4. The student will identify the parts (nodes, antinodes) of a standing wave on a string.
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Wave Properties
Wave Motion
Ms. Kinney
Adapted from Lori Andersen
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What is a Wave?

A disturbance that travels
from one point to another.
 Waves transport energy
without transferring matter.
 A periodic wave is a regularly
repeating series of wave
pulses
 The direction of propagation is
the direction the wave is
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moving
Two Classifications of Waves
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Waves can be classified by
– Medium through which they
are transmitted
– Direction of vibration of
particles
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First type of Classification of
Waves
Mechanical Waves: waves that travel
through a medium.
Sound, Waves on a string
Electromagnetic Waves: waves that do
NOT travel through a medium
Visible light, X-Rays, Radio Waves, Ultraviolet
Rays, Gamma Rays, etc.
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Two Modes of Wave Travel
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Characteristics of a transverse
wave
The dashed line represents the equilibrium
position.
The points of greatest displacement are
called crests (+) and troughs (-).
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Longitudinal wave
The direction of vibration is parallel to the
direction of energy transport.
Example: Sound Wave
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Model of a Longitudinal Wave
http://www.acs.psu.edu/drussell/Demos/waves/
wavemotion.html
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Characteristics of a Longitudinal
Wave
Condensations and Rarefactions in longitudinal waves
correspond to crests and troughs in transverse waves.
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Water Waves
How would you describe the motion
of the particles?
http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.ht
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ml
 Sound
in air can best be classified using
which two of the following terms?
(A) Longitudinal
(B) Transverse
(C) Electromagnetic
(D) Mechanical
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 Sound
in air can best be classified using
which two of the following terms?
(A) Longitudinal
(B) Transverse
(C) Electromagnetic
(D) Mechanical
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 Light
can best be classified using which
two of the following terms?
(A) Longitudinal
(B) Transverse
(C) Electromagnetic
(D) Mechanical
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 Light
can best be classified using which
two of the following terms?
(A) Longitudinal
(B) Transverse
(C) Electromagnetic
(D) Mechanical
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 Crest
is to a transverse wave as
________ is to a longitudinal wave.
(A) condensation
(B) rarefaction
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 Crest
is to a transverse wave as
________ is to a longitudinal wave.
(A) condensation
(B) rarefaction
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 ___________
is to a transverse wave as
rarefaction is to a longitudinal wave.
(A) crest
(B) trough
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 ___________
is to a transverse wave as
rarefaction is to a longitudinal wave.
(A) crest
(B) trough
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 Waves
transfer ___________ without
transferring ___________!
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 Waves
transfer _energy__ without
transferring _matter___!
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Wavelength
Symbol - λ
(lambda)
 Units – any length
units
 Typical values:



Sound Waves: a
few meters
Visible Light
Waves: 400-700
nm (1 nm = 10-9 m)
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Amplitude

The displacement from the equilibrium position
 Units: any units of length
 Symbol: A
 Indicates how much energy the wave carries

Energy is proportional to the square of the amplitude
• Sound ~ loudness
• Light ~ brightness

Wave amplitude is independent of other wave
properties
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Frequency of a Wave

number of complete cycles per second.
 Symbol: f
 Units: hz

1 hz = 1 s-1
The frequency of a wave is always the
same as the frequency of the vibration that
created it.
 Frequency does not change as waves
travel.

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Frequency of a Wave

Frequency and wavelength are inversely
related
 Sound waves, frequency determines the pitch
we hear.
 Light waves, frequency determines the color
we see.
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Period of a Wave





The time for one complete oscillation
Symbol: T
Units: seconds
T = 1/f
If the frequency of the wave is 5 hz, what is the
period?
T = 1/5 = 0.2 s
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Wave Speed

Wave speed depends only on the medium
the wave travels through.


For waves on a string, speed depends on
string thickness and tension.
For sound waves in air, speed depends on air
temperature.
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Wave Speed
•Equation: V=f λ
–V is wave speed in m/s, f is frequency in hz, and  is
wavelength in meters.
–Wave Speed is determined solely by the properties of the
medium through which the wave travels.
–Waves on a String – speed is determined by density of
string and tension.
–Sound Waves – speed of sound in air is determined by
the temperature of the air.
–Light Waves – speed of light is determined by the optical
density of the material.
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Homework: Conceptual Physics
Worksheet
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