Speed of sound in different media:

Sound is a mechanical wave that travels by causing particles of the medium to vibrate and pass on that vibration to neighbouring particles through intermolecular forces; unlike electromagnetic waves, sound absolutely requires a material medium and cannot travel through a vacuum. The speed at which it propagates through a given medium is given by:

v = √(B/ρ)

where B is the bulk modulus of elasticity of the medium (a measure of its resistance to compression) and ρ is its density.

• Water is far less compressible than air, so its bulk modulus B is enormously larger than that of air — this increase in B dominates over the also-larger density ρ of water in the formula above, and the net effect is a substantially higher speed of sound in water.
• Quantitatively, sound travels at roughly 340 m/s in air but around 1480–1500 m/s in water — nearly four to five times faster.
• Physically, this can be understood in terms of intermolecular spacing and coupling: in a liquid such as water, the molecules are packed much more closely together than in a gas like air, and the intermolecular forces linking them are much stronger. This tight coupling means that when one water molecule is disturbed, it transmits that vibration to its neighbours almost immediately, whereas in air, the widely spaced gas molecules must physically travel some distance before colliding with and disturbing the next molecule, which takes comparatively longer.

This same trend continues into solids, which generally transmit sound even faster than liquids, since their particles are even more tightly bound and closely spaced (e.g., sound travels at several thousand metres per second in steel). The claim that sound cannot travel through water at all is factually incorrect — water is in fact an excellent conductor of sound, which is why it is used in technologies like sonar. The claim that sound travels at the same speed in air and water is also incorrect, since their bulk moduli differ enormously despite both being fluids. Similarly, the idea that sound is slower in water because its particles are “further apart” is the reverse of reality — water molecules are much more closely packed than air molecules, which is exactly why sound moves through water more readily and rapidly, not less.