Sound travels fastest through solids. The density of the substance that sound waves move through, as well as its elastic properties, determine its speed.
Sound is a disturbance through a substance that is perceived by the ear and responded to in the brain, as stated by NASA. A substance transmits sound the vibrations move from one molecule to another, creating a wave. The speed at which sound travels changes according to whether the substance it is moving through is a gas, liquid or solid.
When the molecules are far apart, such as in a gas like air, the sound wave travels more slowly because there is a greater distance between the molecules. If the gas is damp, such as humid air, the speed increases. Sound travels faster in a liquid; in fact, the speed is roughly four times greater in water compared to air because of the density of the molecules.
However, sound achieves its fastest speed in a solid, such as metal, where the molecules are tightly bonded and configured more densely than they are in gas or liquid. This means it takes less time for the sound vibration to move from molecule to molecule, so it travels more easily, and therefore, faster.