Applets and sites worth your time

http://www.physicsclassroom.com/

A good source for general help.

Organ Pipe

http://www.walter-fendt.de/ph14e/stlwaves.htm

Doppler Effect

http://www.astro.ubc.ca/~scharein/a311/Sim/doppler/Doppler.html

(Enable "source motion" to make the source move.)

http://www.fisica.uniud.it/~deangeli/applets/Multimedia/Waves_java/Doppler/doppler.htm

http://www.falstad.com/ripple/ex-doppler.html

Waves on a string

http://zonalandeducation.com/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/string.html

http://hep.physics.indiana.edu/~rickv/Standing_Waves_on_String.html

Wave addition

http://www.smaphysics.ca/phys30s/waves30s/waveadd1.html

Interference

http://www.walter-fendt.de/ph14e/interference.htm

http://paws.kettering.edu/~drussell/Demos/superposition/superposition.html