Demos about Traveling Waves

(Note: For many of these animations, the QuickTime 7 plugin for Firefox will only show the first second of time.  Download the file instead.)

This animation shows that in the time of one period, a wave travels a distance of one wavelength.

This animation demonstrates beats, where two waves of very similar wavelength combine to alternately reinforce or cancel out each other.  Note that the shape of the combined wave remains constant; the variation in time is only experienced by a person sitting in one place as the wave mores past.

Doppler Effect

These are from Physics 2000, which has a variety of excellent applets:

• "Doppler Effect I":  Shows how a moving source results in changes in the wavelength (and hence frequency) of the emitted sound.
• "Doppler Effect II (sound)":  If you have a sound card in your computer, this lets you hear a sound source passing by.  (As if you've never heard this before.)

This is from Virtual Physics Laboratory:

• Doppler Effect applet: Allows a lot of control, including making a shock wave (sonic boom).  A check box can turn on a detector as well.

And here is one where you have 2D control of the source velocity.

Reflection and Transmission

This PDF file enumerates what happens when waves reach boundaries between media.

Interference

Also from Virtual Physics Laboratory:  Double Slit Interference