Point source: Doppler effect and shock wave

Things to try:

    1. wave speed, wave length and the speed of the point source can be adjusted

    2. Click near tip of the corresponding arrows and drag the mouse

    3. Click the mouse button within the window to suspend the animation,
        click it again to continue.
       The mouse position(related to initial poition) will be shown.
       Left click the mouse button and drag it to show the displacememt.
       Right click the mouse button and drag the mouse to show the angle.

    4. Click at the center of the red ruler to drag it.
        Click at either end and drag the mouse to change its length.

    5. Shock wave is formed if the point source moving faster than the wave speed.