• 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