Mechanical waves, such as sound waves, require a medium to propagate, which can be solids, liquids, or gases. The essential property of this medium is its ability to respond to mechanical actions, as described by Hooke's Law, where increased distention leads to a proportional counter-force. This response allows for the energy of the wave to travel through the medium via compression and stretching of its molecules. The wave itself is not the entire medium moving, but rather the localized reaction of the medium's structure to the applied forces. Understanding these properties is crucial for analyzing how mechanical waves function in various environments.