This java applet show the Doppler effect.
Click inside the simulation region to select initial position for wave center.
While press down the mouse, drag the mouse to change the velocity for the wave source. (This is a moving point source)

The wave speed and the period of the wave (f=2*?/T) is adjustable by sliders.
If the source speed is smaller than wave speed. An ear gif image will appear in the simulation region(you can drag it to other position).
You will hear a sound click when the wave front pass the ear. (The frequency of the click sound is related to Doppler effect)

You will find wave pattern for shock wave when the source speed is larger than wave speed.
applet width="645" height="373" code="users.ntnu.fkh.dopplerxy_pkg.dopplerxyApplet.class" codebase="/ntnujava/ejs4/" archive="ejs_dopplerxy.jar" name="dopplerxy" id="dopplerxy" mayscript="true" /applet[/hide]

translate strings in simulation to different language format before download
Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
Download EJS jar file(1538.9kB):double click downloaded file to run it. (66 times by 44 users) , Download EJS source (14 times by 12 users) View EJS source

The following is a flash demo