How do density and elasticity affect the speed of sound?

The speed of sound in a medium is fundamentally determined by its elastic modulus and its density. Specifically, the wave velocity is proportional to the square root of the ratio of the medium's elastic modulus to its density.1

• Elasticity: This refers to the ability of a medium to be compressed and subsequently return to its original volume or shape. A higher elastic modulus (such as the bulk modulus in fluids) indicates a material that is more resistant to compression, which generally facilitates faster transmission of sound waves.12
• Density: This is the mass per unit volume of the medium. Because density appears in the denominator of the velocity equation, an increase in density—while holding elasticity constant—typically results in a decrease in the speed of sound.1

In essence, sound propagates as an elastic wave, where the interplay between these two properties dictates how quickly particles can restore their position after being displaced.2