# Resonance of an Air Column

## Homework Statement

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When a stream of air is directed over the end of a 40 cm long piece of plastic pipe, open at both ends, a sound is produced.
(a) Explain why this occurs
(b) If the bottom end of the pipe is covered, what will happen to the pitch of the sound? Explain

## Homework Equations

Ln = (n x λ)/2
F1 = v/(2 x L1)
Ln = (2n-1) x (λ/4)
F1 = v/(4 x L1)

## The Attempt at a Solution

For a), my best guess is that the stream created vibrations in the air molecules which caused the plastic pipe to resonate at its natural frequency and that created a sound

For b), I recreated this question by blowing over a straw and noticed the pitch decreases when the bottom is covered, and I know that a decrease in pitch means a decrease in frequency, but I do not know why this happens.

A nudge in the right direction would be appreciated. Thank you.

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.Scott
Homework Helper
You are creating a standing wave in the straw. Opening or closing the end of the straw changes how the wave reflects of that endpoint.

I see. Is the standing wave created by vibrations in the pipe from the moving air?

haruspex