# Waves

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```					            • Disturbances
• All waves carry energy
• Waves displace matter
– Waves do NOT carry matter

http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
Medium
• Medium – the material a wave travels
through
–When sound travels through air,
the air is the medium
–When sound travels through a
solid, such as glass, the glass is the
medium
Types of
Waves
Transverse Waves
• Examples: water waves, light waves, waves in a
string or a rope, secondary seismic waves
• Displace the medium perpendicular to the
direction the wave travels

http://www.physicsclassroom.com/Class/waves/U10L1c.html
Crest
Wavelength
amplitude

Trough
Longitudinal Waves
(compression waves)
• Example: sound waves, primary seismic
waves
• Displace the medium parallel to the
direction the wave is moving

http://www.physicsclassroom.com/Class/waves/U10L1c.html
http://www.physicsclassroom.com/Class/waves/U10L2a.html

• http://members.aol.com/nicholashl/waves
/movingwaves.html
(Wave animation)
amplitude     compression

wavelength
rarefaction
Wave
Interactions
Reflection
• A wave “bounces
back” when it
encounters a new
medium
• Law of reflection:
the angle of
reflection equals
the angle of
incidence
Reflection
Reflection from a
fixed boundary

Reflection from
a soft boundary

http://www.kettering.edu/~drussell/Demos/reflect/reflect.html
Some Uses of Reflection
•   Mirrors
•   Communications
•   Sonar
Refraction
• A wave changes speed and direction
(bends) when it enters a new medium
Waves travel at different
speeds in different mediums
(due to density differences)
When a wave strikes the
boundary between mediums at
an angle, one part of the wave
slows down before another,
and the wave bends
Refraction animation - http://users.wpi.edu/~hkim/physics/refraction.swf
http://www.williamson-labs.com/optical-body.htm

Light reflected from fish is bent as it travels
from water into the air.
To the viewer, it appears as if the fish is
along a straight line (the refracted ray)
Diffraction
• A wave bends as it
passes around a
barrier
• Used in
spectroscopy
universe from the
colors of light
emitted from
objects)
Interference
• Two or more waves combine
– Because waves are not matter (they are
disturbances that displace matter), more than
one wave can occupy the same space at the
same time
– This is called superposition
Interference (continued)
• When two crests meet, their amplitudes
• When a crest and a trough meet, their
amplitudes cancel each other out
(destructive interference)
• The resulting wave is the sum of the
amplitudes at all points
Constructive and Destructive
Interference
Superposition of Waves
Constructive and Destructive
Interference

```
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 views: 5 posted: 3/15/2012 language: English pages: 21