in chapter 13 we went over: work › how work relates to force and distance transfer and...
TRANSCRIPT
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Chapter 15Waves
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15.1: Waves transfer energy
In chapter 13 we went over: Work
› How work relates to force and distanceTransfer and conservation of energy
› Power Now we will learn:
› How forces create waves› How waves transfer energy› How waves are classified
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A wave is a disturbance
Wave:› The disturbance that transfers energy from
one place to another Can transfer energy over distance without
moving matter the entire distance.
› Ocean waves travel kilometers without the water itself moving the same distance-the water simply moves up and down (disturbance) transferring its energy
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Forces and waves
Forces start a disturbance which sends a wave through the material:
Rope waves:› If I flick the rope by applying a force
upward then quickly apply the opposite force down, it sends a wave through the rope.
› Both forces are required to start a wave
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Water waves:› When an object is dropped into the water,
the force applied causes waves to move through the water
› D:\wave-interference_en.jar
Earthquake waves:› Sudden release of energy that has built up
in the rock from a pushing and pulling (force) causes energy waves to be transferred through the ground
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Materials and waves:
Medium:› Any substance that a wave moves through
Water is the medium for ocean waves Rope is the medium for a rope wave
Mechanical waves:› Waves that transfer energy through matter
What is matter?
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Energy and waves:
Think about an earthquake:› What type of energy is transferred during
an earthquake (kinetic, potential, or mechanical)
› The disturbance causes the ground to shake from side to side and up and down
› As the energy is released, it travels in a wave but the ground itself does not travel with the wave
› Faults and Earthquakes
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Waves can be classified by how they move
Transverse waves:› The direction in which the wave travels is
perpendicular, or at right angles, to the direction of the disturbance
› “transverse” means across or crosswise› Look at the rope wave:
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Longitudinal waves:› A wave that travels in the same direction
as the disturbance Examples are:
› Sound waves Molecules of air are set in motion which
vibrate quickly causing more air molecules to vibrate
› Slinky wave demo: If I pull the slinky back straight and release
it, the coils move forward and backward.
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Math review: wave height
When tracking and recording the height of waves in the ocean, scientists use:
Mean:› The average of the recorded heights
Median:› The middle value when all values are
recorded from least to greatest Mode:
› The value that occurs the most out of the data set
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15.2: Waves have measurable properties
Measuring wave properties:› Crest:
The highest point or peak of a wave› Trough:
The lowest point or valley of a wave
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Amplitude:› The distance between the middle of the
crest to the middle of the trough in a transverse wave.
› Indicates how much energy the wave is carrying (bigger the wave, the more energy)
Wavelength:› The distance from the crest of one wave to
the crest of the next wave› Can also be measured from trough to
trough
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Frequency:› The number of waves passing a fixed point
in a certain amount of time› “frequent” means often
Frequency and wavelength are related:› If the frequency increases, the wavelength
shortens› If frequency decreases, the wavelength
increases
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Graphing wave properties
http://www.classzone.com/books/ml_science_share/vis_sim/wslm05_pg18_graph/wslm05_pg18_graph.html
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Measuring wave speed
Speed = wavelength times frequency S=λf
S means speed λ (Lamda) means wavelength f means frequency
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15.3: Waves behave in predictable ways
Reflection:› The bouncing back of a wave after it
strikes a barrier Refraction:
› The bending of a wave as it enters a new medium at an angle other than 90 degrees
Diffraction:› The spreading out of waves through an
opening or around the edge of an obstacle
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Reflection
reflection and refraction
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Refraction
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Diffraction› D:\wave-interference_en.jar
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Interference:› The meeting and combining of waves› They can add to or take away energy from
each other Constructive interference:
› The adding of two waves› Makes a larger wave out of two smaller
waves› When joined perfectly, the new amplitude
equals the combined amplitudes of the two original waves
Waves can cancel each other out
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Constructive interference
Destructive interference