This java applet let you visualize the difference between transverse wave and longitudinal wave.

Longitudinal
and Transverse

You will find both moving wave and standing wave.

Usage :

1. You can view transverse wave or longitudinal wave from the above selection.
2. Those blue lines on the left are dispacements relative to the equilibrium point,
    while those red lines on the right are relate to velocity of wave medium at those points.
3. The distance between two circle dots are 0.5 wavelength. (moving out of phase)
    Click and drag left mouse button to move them horizontally but keep the same distances.
    Click the right mouse button to locate position for one of the black dot,
        drag the right mouse button to position the second one.
        The distance between dots will be shown in unit of wavelength.
4. Click the right mouse button and release it at the same location to toggle the animation.