It is easier for sound waves to go through solids than through liquids because the molecules are closer together in solids. Similarly, it is harder for sound to pass through gases than through liquids, because gaseous molecules are farther apart. The speed of sound is faster in solid materials and slower in liquids or gases. The speed of sound is also different for different types of solids, liquids, or gases. Some materials, like nickel or iron, are more elastic than others.
Elasticity describes how quickly the molecules return to their original positions.
Molecules that return to their original shape quickly are ready to move again more quickly, thus can vibrate at higher speeds. Sound can travel faster through mediums that vibrate faster. Thus, sound travels faster through elastic solids like nickel or iron than through solids like lead, which is less elastic. The density of a medium also affects the speed of sound. Density describes the mass of a substance per volume.