This document discusses key properties of sound including: 1) Sound is a type of energy that moves through matter as vibrations called sound waves. Sound waves can be longitudinal or transverse. 2) Sound travels through solids, liquids, and gases at different speeds depending on how closely packed the particles are. It travels fastest through solids and slowest through gases. 3) Absorption occurs when sound waves hit a material and their energy is transferred to thermal energy, helping to cover rooms with absorbing materials.