Sound squashes and stretches the air along its travel; we graph the pressure against position, not a sideways string.
Example
Sound squashes and stretches the air along its travel; we graph the pressure against position, not a sideways string. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Sound squashes the air along its travel
Sound is a longitudinal wave: the air does not bob sideways like a string — it squashes and stretches back and forth along the same direction the sound travels, making regions of high and low pressure that move outward.
sound: compressions and rarefactions along the travel
We graph the pressure, not a sideways string
To use our wave tools we plot the pressure against position. Read this carefully: the up-and-down of this curve is PRESSURE, not the air moving sideways. The crests are compressions, the troughs are rarefactions. With that picture, wavelength and frequency mean the same as for any wave.
the curve is pressure vs position, not a transverse string
Louder sound means a larger pressure swing
A compression is pressure above the usual air pressure; a rarefaction is pressure below it. In this simplified picture, a larger pressure swing means a louder sound, but it is still pressure changing along the travel direction, not air moving sideways.