How it works: Sound travels through the air as a longitudinal wave (top). Particles oscillate back and forth, creating areas of high pressure (compressions, where particles bunch up) and low pressure (rarefactions, where they spread apart).
We often graph sound as a transverse wave (bottom) for easier analysis. The peaks (crests) of the sine wave represent maximum pressure, which align perfectly with the red wave fronts where particles are most densely packed.
Try it: Change the note to see how higher pitches (frequencies) result in shorter wavelengths. The speed of the wave moving across the screen remains constant, just as the speed of sound is constant in the air.