Disturbances All waves carry energy Waves displace matter –Waves do NOT carry matter...
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Transcript of Disturbances All waves carry energy Waves displace matter –Waves do NOT carry matter...
• 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 Medium – the material a wave travels throughtravels through– When sound travels through When sound travels through
air, the air is the mediumair, the air is the medium– When sound travels through a When sound travels through a
solid, such as glass, the glass is solid, such as glass, the glass is the mediumthe medium
Types of Types of WavesWaves
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
Trough
Wavelength amplitu
de
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://members.aol.com/nicholashl/waves/movingwaves.html
(Wave animation)
http://www.physicsclassroom.com/Class/waves/U10L2a.html
wavelength
amplitude
compression
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• Radar• Sonar
Refraction
• A wave changes speed and direction (bends) when it enters a new medium
Refraction animation - http://users.wpi.edu/~hkim/physics/refraction.swf
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
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)
http://www.williamson-labs.com/optical-body.htm
Diffraction
• A wave bends as it passes around a barrier
• Used in spectroscopy (learning about the 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 are added (constructive interference)
• 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