how will the air temperature in a room affect the pitch of organ pipes?
The speed of sound in air is determined by the properties of the air molecules -- speed, number density (number per unit volume), individual particle's inertia (mass)...
The speed of sound and the frequency determine the wavelength... and in the case of an organ pipe, the fundamental frequency (pitch) is determined by the length of the pipe (some frequencies of sound will "resonate" in the pipe... i.e. build up via constructive interference... and some frequencies will not).
To work through this in steps: do you know how the speed of sound changes with temperature?
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