Summary
Superposition of waves
Waves can be combined together in such a manner as to cause either constructive or destructive interference.
Reflection
One dimensional waves reflecting from boundaries can be decomposed into two component waves. The phase of the reflected wave depends on the kind of boundary. Three dimensional waves reflecting from boundaries create more complicated patterns.
Refraction
When waves travel into a medium with a different wave speed they are refracted and travel in a different direction. This change of direction can be found from Snells law.
Diffraction
Diffraction involves the bending of waves as they pass through narrow openings or around corners.
Interference
Patterns of constructive and destructive interference are produced when two sources (or more) generate waves that combine together in such a manner as to cause either constructive or destructive effects.
Moving sources
Sound sources moving towards an observer are perceived as having a higher frequency, and vice versa.