Sound waves propagate in all directions because they are a type of mechanical wave that requires a medium (such as air, water, or solids) to travel through. When a sound is created, it sets off a series of compressions and rarefactions in the surrounding medium, which propagate as a wave. This wave spreads out spherically from its source, expanding in all directions.
The motion of particles in the medium when a sound wave passes through is more complex. As the sound wave travels, the particles of the medium vibrate back and forth in the same direction as the wave propagates. This back-and-forth motion is called longitudinal motion. However, the particles do not vibrate in all directions simultaneously.
When a sound wave passes through, the particles in the medium oscillate around their equilibrium positions. In the case of a sound wave traveling in air, the air particles move back and forth parallel to the direction of the wave propagation. This compression and rarefaction of the air particles result in the alternation of regions of higher and lower pressure, creating the characteristic pattern of a sound wave.
While the motion of the individual particles is along the same line as the sound wave, the wave itself expands spherically in all directions from its source. This is because each particle interacts with its neighboring particles, transferring the energy and motion along the chain. The collective motion of all the particles results in the sound wave spreading out in a spherical pattern, radiating from the source.
It is important to note that once the sound wave propagates through the medium, the particles return to their equilibrium positions, and their overall displacement is minimal. The primary motion occurs in the direction of the wave propagation, but the wave itself spreads out in all directions, allowing sound to be heard from different angles around the source.