Which factors affect the speed of sound in water?

• A. Salinity
• B. Pressure
• C. Temperature
• D. All of the above

Answer: (D)

Speed of sound in water is controlled by how easily the fluid can be compressed (its stiffness) and how much mass there is to move (its density). A handy way to think about it is the relation c ≈ sqrt(B/ρ), where B is the bulk modulus (a measure of compressibility) and ρ is density. A stiffer medium or a less dense one transmits pressure waves faster.

Temperature affects both density and compressibility. As water warms, it becomes less dense and its compressibility changes in a way that, overall, increases the speed of sound. In practice, warmer seawater carries sound faster.

Pressure increases with depth, which raises the bulk modulus more than it raises density. The net effect is a faster propagation of sound in deeper water.

Salinity adds dissolved salt, which increases both density and stiffness slightly. This shifts speed upward, though the change is typically smaller than the changes caused by temperature or pressure.

Since each of these factors influences how quickly a pressure disturbance travels, all three affect the speed of sound in water.