What defines a mechanical wave?

A mechanical wave is defined by its requirement to travel through a material medium, which can be a solid, liquid, or gas. This definition emphasizes that mechanical waves involve disturbances that move through these materials by transferring energy without the permanent displacement of the medium itself. For example, when a person creates ripples in a pond by throwing a stone, the water molecules oscillate and pass energy along, but they do not travel with the wave itself.

The other options do not meet the criteria for a mechanical wave. Waves that do not require a medium are classified as electromagnetic waves, while those traveling through a vacuum fall into the same category, as they can propagate through empty space. Finally, waves generated by a periodic electric field pertain to electromagnetic radiation rather than mechanical waves. This understanding clarifies why choice C is the only option that correctly identifies the essential characteristic of mechanical waves.