Click on the flag to start. This is an animation that illustrates the nature of sound (a longitudinal wave propagating through through the air) and how that links to variations in air pressure. When sound is captured by a microphone, the variations in air pressure translate to variations in voltage. The wave amplitude and frequency is constant. You can use the toggle on the lower right to enable using the microphone, in which case the amplitude varies according to the input's amplitude. (Scratch has no way of capturing frequency information so, when the microphone is used, the animation is illustrative but not accurate).
