Download PPT Waves 12

What are waves?
These are just one of many
examples of waves...
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Waves Are a Form of Harmonic Motion
Motion that repeats over and over…
The pendulum is an example.
“There and Back Again” -- this represents 1 cycle or “period.”
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Scientists use pendulums to determine
predictable cycles in things such as:
Because these cycles are predictable,
we can use them to “mark” time.
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(Harmonic Motion)
Rhythmic disturbances that
carry energy through
matter and space
Results when matter
vibrates.
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Waves can travel through space.
Waves are made when you speak.
And make the light
you see as light.
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How dolphins
communicate
Waves can
travel
through a
medium.
Music from
your radio
to your ear
Solid – earth quake
is the material in which a wave moves.
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But there are some waves that don’t
travel through a medium…
Microwaves
Radio
Larger Waves
Infrared
Visible
X-Ray
Ultraviolet
Gamma
Smaller Waves
Electromagnetic waves
such as visible light travel throughout
“matter-less” space.
More on this later...
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Waves can be easily understood through...
...a wave whose oscillations are perpendicular
to the direction the wave travels.
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Crest – top of the wave
Trough
Crest
Trough – bottom of the wave
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Wavelength
Nodal Line
Amplitude
Wavelength – distance to include 1 crest and 1
trough- represented by (‫ – ג‬Lambda) symbol
or
Amplitude – (volume) height of crest or trough
from nodal line measured in decibels (db) and is
the total energy of the wave.
Nodal Line-resting line
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Wave frequency is the amount of waves
that move through a point per second
and is measured in the units of Hertz (Hz).
Point A
The diagram above shows 3 waves going
through point A in 1 second.
The frequency would be 3 Hz.
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Calculating the Velocity of a Wave
To find the velocity or speed of a wave, use the
following equation:
Velocity = Wavelength X Frequency
V=‫ג‬xf
V = Velocity in m/s
(‫ = )ג‬Wavelength in meters (m)
f = Frequency in hertz (Hz)
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Calculating the Velocity of a Wave
A wave moves through water. The length
of the wave is 5 meters. The frequency
is 2 waves per second (2 Hz). What is
the velocity of the wave?
Remember the 4 step process to
solving equations …
= 5 m
F = 2 Hz
V = 10m/s
Formula
Substitute
Answer
V= x f
5m x 2Hz
10 m/s
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Do problems 1, 2 & 3
in your notes.
Hint: You may have to manipulate the
formula – make a triangle.
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Longitudinal Waves
Also called compressional waves.
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Longitudinal Waves
Compression - part where molecules are pushed together
Rarefaction - part where molecules are spread apart
nodal line
Compression
Wavelength
amplitude
Rarefaction
Wavelength – 1 Compression and 1 Rarefaction
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Reflection
• the bouncing back of a wave as it strikes a hard surface.
• Reverberation –
• Combination of reflected waves
• Multiple Echoes like in concerts
• Example: when a water wave from the ocean hits the
beach
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Diffraction
• when waves spread out past the edge of a barrier or
through holes in the barrier.
• Example: You can hear someone talking around a
corner, because the waves move beyond the wall.
This is going to be
a great surprise!
Not anymore!
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Refraction
• To change the direction of a wave as it passes from one
medium to another.
• The frequency doesn’t change, but the speed and
wavelength do – they slow down.
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Absorption
• A wave that can be absorbed by the medium
material and disappear.
• The amplitude of the wave gets smaller and
smaller.
• Examples: sponge absorbs water wave
heavy curtain absorbs sound waves and
dark glass absorbs light waves
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Interference
• When 2 or more waves pass through a medium at the
same time.
Constructive
Hit the nodal line
together.
Basically music.
IN PHASE
Destructive
Hit the nodal line at
different times.
Basically noise.
OUT OF PHASE
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Natural Frequency and Resonance
Natural Frequency
– A special frequency at which objects vibrate if they are
disturbed
– All things in the universe have a natural frequency
– Changing the natural frequency:
• of a string-by tightness, lengthening or weight of
string
• in a system-change the factors that affect the size,
inertia or forces in the system.
Resonance
– Having the natural frequency of the system
exactly in tune with your forceamplitude grows, Example-swing set
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Standing waves on a string
Standing wave
– A wave that is trapped in one spot
Fundamental
– Natural frequency of a wave
Harmonic
– Fundamental and multiples of its frequency
– Node-point where the string does not move
– Antinode-points of the greatest amplitude
– Wavelength is the length of one complete
“S” shape of the string
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Seismic Waves
Seismic waves are vibrations that travel through
Earth, carrying energy released during an
earthquake.
• Earthquakes produce three main types of
seismic waves:
• P waves
• S waves
• Surface waves
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P waves
P waves are longitudinal waves similar to sound
waves.
• P waves compress and expand the ground
like an accordion.
• They are the fastest seismic waves.
• They can travel through both solids and
liquids.
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S waves
S waves are transverse waves, like light and
other electromagnetic radiation.
• S waves cause particles in the material
they pass through to vibrate at right
angles to the direction in which the waves
move.
• Unlike P waves, S waves cannot travel
through liquids.
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Surface Waves
Surface waves are waves that develop when seismic
waves reach Earth’s surface.
• Surface waves move more slowly than P waves or
S waves.
• Surface waves usually produce larger ground
movements and more damage than other types of
seismic waves.
• Some surface waves are transverse waves, and
others have a rolling motion similar to ocean
waves.
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Earth’s liquid
outer core
blocks S waves
and refracts P
waves. The
result is a
shadow zone
where no direct
seismic waves
from an
earthquake are
detected.
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