Longitudinal Standing Waves - Walter Fendt
This applet shows the pressure and displacement variations as air resonates inside a tube (such as a trumpet or organ pipe. Note that there are many frequencies and wavelengths that will resonate, and that as the frequency increases, the wavelength decreases. This is why short instruments can only make high pitched notes.f\
Adjust the various settings on the right, and follow the motion of individual particles in the tube.
Click http://www.walter-fendt.de/ph14e/stlwaves.htm link to open resource.