phys 20 lessons unit 6: simple harmonic motion mechanical waves lesson 6: mechanical waves
TRANSCRIPT
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PHYS 20 LESSONS
Unit 6: Simple Harmonic
Motion
Mechanical Waves
Lesson 6: Mechanical Waves
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Reading Segment:
Mechanical Waves
To prepare for this section, please read:
Unit 6: pp.18 - 19
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MECHANICAL WAVES
There are two types of mechanical waves:
1. Transverse Waves
- wave motion is perpendicular to particle
vibration
2. Longitudinal Waves
- wave motion is parallel to particle vibration
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Transverse Waves
Consider a vertical vibration at the end of a spring:
spring (medium)
Vibration
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wave motion
Vibration
The vibration is the source of energy for the wave.
It creates a disturbance in the medium, moving away from the
source.
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wave motion
Vibration
All particles are vibrating perpendicular to the wave motion.
They never move left or right.
Thus, it is called a transverse wave.
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Crests
Vibration
Troughs
The top of the transverse wave is called the crest.
The bottom of the wave is called the trough.
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Equilibrium
Vibration
The rest position of the medium is called the equilibrium
position. This is where the particles would be if there was
no wave going through it.
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A
A
Vibration
The maximum amplitude (A) is the energy of a wave.
It is the distance from equilibrium to the crest
(or from equilibrium to the trough).
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Vibration
The wavelength () is the length of 1 cycle or repetition
of the wave.
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Vibration
The wavelength could be the length from crest to crest.
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Vibration
The wavelength could also be the length from trough
to trough.
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Vibration
Note: If two particles are one wavelength apart, they will move
identically as the wave train goes through the medium.
We say that they are in phase.
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Animations
Transverse Waves
http://surendranath.tripod.com/Applets.html
Go to: "Waves"
"Transverse Waves"
"Transverse Waves"
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Animations
Anatomy of Transverse Waves
1. http://id.mind.net/~zona/mstm/physics/waves/partsOfAWave/waveParts.htm
2. http://id.mind.net/~zona/mstm/physics/waves/introduction/intr
oductionWaves.html
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Longitudinal Waves
Consider a horizontal vibration at the end of a spring:
Vibration
spring (medium)
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Direction of wave
Vibration
The vibration is the source of energy, and it causes
a horizontal disturbance in the medium.
The wave moves away from the source.
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Direction of wave
Vibration
The particles are always vibrating parallel to the wave motion.
Thus, this is called a longitudinal wave.
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C C C C
Vibration R R R R
The regions of high density are called compression (C) regions.
The regions of low density are called rarefaction (R) regions.
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Vibration C C
The wavelength of a longitudinal wave is the distance
between two successive compression regions
i.e.
"from C to C"
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Animations
Longitudinal Waves
http://surendranath.tripod.com/Applets.html
Go to: "Waves"
"Longitudinal Waves"
"Transverse Waves"
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Note:
Due to friction, waves will lose their energy
- transverse waves lose their amplitude
- longitudinal waves will lose their density
But, the frequency will never change.
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Surface waves (e.g. water waves) are circular waves
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Surface waves (e.g. water waves) are circular waves
Upper particles move
in circles
Lower particles move
in ellipses
Deep particles move back
and forth
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Earthquakes create all 3 kinds of waves
Primary (P) waves
- the first to arrive
- longitudinal waves
Secondary (S) waves
- second to arrive
- transverse waves
Surface waves
- last to arrive
- these do the most damage
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Animation
Earthquakes
1. http://www.pbs.org/wnet/savageearth/animations/earthquakes/
main.html
2. http://schools.matter.org.uk/Content/Seismology/index.html
3. http://encyclopedia.thefreedictionary.com/Seismic%20wave