What name is given to sections of longitudinal waves where the medium is "stretched out"?

The sections of longitudinal waves where the medium is "stretched out" are called rarefactions.

In longitudinal waves, the particles of the medium move parallel to the direction of the wave propagation. This movement creates alternating sections of compression and rarefaction.

1. Compressions are the regions where particles are close together, resulting in increased pressure.
2. Rarefactions, on the other hand, are the regions where particles are spread apart, leading to decreased pressure.

This alternating pattern is essential for the wave to travel through the medium. For example, in sound waves traveling through air, the areas of rarefaction allow the sound to propagate by creating zones of low pressure that follow the zones of high pressure (compressions). Understanding these concepts is fundamental to the study of wave mechanics and acoustics.