When a sound source vibrates, it creates alternating regions of high and low pressure in the surrounding air, known as compressions and rarefactions, respectively. A vibrating object pushes air forward, creating a compression (high pressure), and then retracts, creating a rarefaction (low pressure). This alternating pattern of compressions and rarefactions propagates outward from the source as a sound wave.
Diagram and Explanation:
Imagine a tuning fork vibrating near a microphone:
1. Compression:
When the tuning fork prong moves outward, it compresses the air molecules in front of it, creating a region of higher pressure, which we call a compression.
2. Rarefaction:
When the tuning fork prong moves inward, it creates a region of lower pressure, where the air molecules are spread apart, called a rarefaction.
3. Propagation:
As the tuning fork vibrates back and forth, this alternating pattern of compressions and rarefactions moves away from the fork, traveling through the air as a sound wave.