Here's why:
* Absorption: When a wave enters a material, its energy can be transferred to the particles within the material. This causes the particles to vibrate, and the energy of the wave is essentially "absorbed" by the material. This is why certain materials are opaque to light - they absorb the light energy rather than reflecting it.
* Reflection: This occurs at the surface of a material when a wave encounters a change in medium. The wave bounces back off the surface.
* Refraction: This happens when a wave passes from one medium to another and changes direction due to a change in speed. This occurs at the boundary between two materials.
* Diffraction: This occurs when a wave encounters an obstacle or passes through a narrow opening. The wave spreads out, bending around the obstacle or opening. While diffraction can happen within a material if there are internal structures, it's primarily associated with interaction at the boundary of a material.
Therefore, absorption is the wave interaction that primarily takes place within a material.
