Sound waves are caused by the vibration or oscillation of particles in a medium, such as air, water, or solids. When a sound is produced, it creates a disturbance in the particles of the medium, causing them to compress and expand.
The compression and expansion of the particles occur due to changes in pressure. Let's take the example of sound traveling through air:
Compression: When a sound wave is generated, it creates a region of increased pressure called a compression. This compression occurs when the source of the sound pushes air molecules together, increasing their density. The molecules become closer to each other, resulting in a higher pressure region.
Expansion: Following the compression, the sound wave creates a region of decreased pressure called an expansion or rarefaction. This occurs when the source of the sound pulls air molecules apart, decreasing their density. The molecules become spread out, resulting in a lower pressure region.
As the sound wave propagates through the medium, these compressions and expansions continue to occur in a repeating pattern, creating a series of alternating high-pressure and low-pressure regions. This pattern of compression and expansion is what we perceive as sound.
It's important to note that sound waves are longitudinal waves, meaning the particles of the medium vibrate parallel to the direction of wave propagation. This is in contrast to transverse waves, where the particles oscillate perpendicular to the direction of wave motion.