Waves
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 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 Radar 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 (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