1 what are waves? these are just one of many examples of waves
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What are What are waves?waves?
These are just one of many examples of waves...
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Waves Are a Form of Harmonic MotionMotion 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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Rhythmic disturbances that carry energy
through matter and space
(Harmonic Motion)
Results when matter vibrates.
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Waves are made when you speak.
Waves can travel through space.
Waves c
an make th
e
earth m
ove and shake.
And make the light you see as light.
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Waves can
travel through a medium.
is the material in which a wave moves.is the material in which a wave moves.
How dolphins communicate
Solid – earth quake
Music from your radio to your ear
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But there are some waves that don’t travel through a medium…
Electromagnetic waves such as visible light travel throughout
“matter-less” space.
More on this later...
Radio
Microwaves
Infrared Ultraviolet
VisibleX-Ray
Gamma
Larger Waves Smaller Waves
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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 – bottom of the wave
Crest
Trough
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Am
plitu
de
Am
plitu
de
Wavelength
oror
Wavelength – distance to include 1 crest and 1 trough- represented by (ג – Lambda) symbol
Amplitude – (volume) height of crest or trough from nodal line measured in decibels (db) and is the total energy of the wave.
Nodal Line
Nodal Line-resting line
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Wave frequency is the amount of waves that move through a point
per secondand is measured in the units of Hertz (Hz).
The frequency would be 3 Hz.
Point APoint A
The diagram above shows 3 waves going through point A in 1 second.
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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 = ג x fV = Velocity in m/s
Wavelength in meters (m) = (ג)
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?
= F =V =
2 Hz5 m
10m/s
Formula Substitute Answer
V= x f 5m x 2Hz 10 m/s
Remember the 4 step process to solving equations …
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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 WavesLongitudinal WavesAlso called compressional waves.
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Longitudinal WavesLongitudinal Waves
Compression
Rarefaction
Wavelength
Rarefaction - part where molecules are spread apart
Compression - part where molecules are pushed together
Wavelength – 1 Compression and 1 Rarefaction
nodal line
amplitude
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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 Destructive
Hit the nodal line together.
Basically music.
IN PHASE
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 force-amplitude 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
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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 WavesSurface 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.