Which statement accurately compares the speed of sound in seawater to that in air at sea level?

• A. Slower than air
• B. Approximately the same as air
• C. Much slower than air
• D. Faster than air

Answer: (D)

Sound speed hinges on how quickly a medium can transmit a pressure disturbance, which comes from the medium’s density and how compressible it is. Water is dense and only mildly compressible, so its bulk modulus is large. Using the relation v ≈ sqrt(B/ρ) gives a very high speed in seawater—about 1500 meters per second. In air at sea level, the density is far lower and the medium is more compressible, so the speed is around 343 meters per second. This makes sound travel much faster in seawater than in air, by roughly four to five times under typical conditions. Temperature and salinity adjust the exact numbers, but the general trend remains that seawater is the faster medium.