In a longitudinal wave, what is the term for the area where particles are spread apart?

In a longitudinal wave, the area where particles are spread apart is referred to as rarefaction. In this type of wave, the propagation occurs through compressions and rarefactions. Compressions are regions where particles are close together, whereas rarefactions are the regions in the wave where the particles are more spread out. This spreading apart allows the wave to travel through the medium.

Understanding rarefaction is crucial because it helps in visualizing how sound, for example, travels through air. As sound waves move, they create alternating regions of high and low pressure, and the rarefactions correspond to those lower pressure regions where the particles are not as densely packed. This concept underpins the nature of how energy is transmitted in longitudinal waves, such as sound waves.