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
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.