Understanding Standing Waves in Open Tubes

[WRS]

Homework Statement

standing waves

Relevant Equations

harmonics, wavelength

Hello everyone.

I'm having some trouble understanding waves. Particularly standing waves in an open tube.

So we have an open tube, someone blowing air into it creating a first harmonic and we have particles oscillating back and forth. The particles oscillating pressurize where the air displacement nodes exist.

This is a bit intuitively conflicting with the idea of a standing wave.. That being a standing wave is a wave in which the peaks/troughs of the wave occur at the same points.

How is it that I can blow on a tube, have noticeable air come out of the other side yet it produces a 'non moving wave' while air particles are being blown out the other end?

Is it due to the fact that blowing on a tube creates a momentary high pressure inside the tube? So when I blow into the tube the air is essentially being 'pushed back' into the tube when it meets the end of the tube... creating oscillations of pressure? I feel I'm missing something here.

Thank you very much

 

[haruspex]

I don't see the conflict. It's just that the air in the pipe undergoes longitudinal oscillations, whereas your canonical standing wave model has lateral oscillations.
At some instant, the standing wave peaks and troughs are at a maximum; correspondingly, there are instants when there is max displacement one way at one point in the tube and max displacement the other way half a wavelength further on.

When creating a sound by blowing, the movement of air through the tube is largely irrelevant. Typically one either blows across a hole or through a reed to create the initial sound. Certainly the molecules are moving much faster in executing their oscillations than in traversing the tube.