The speed of sound depends on the medium through which it travels. It moves fastest in solids, slower in liquids, and slowest in gases. This variation is due to the differences in particle arrangement and intermolecular forces in different states of matter.

Why Does the Medium Matter?

Sound is a mechanical wave — it travels by making particles in a medium vibrate and pass the energy along. The closer and stronger the connection between particles, the faster sound can be transmitted.

• In Solids: Particles are tightly packed and strongly bonded. Vibrations are transferred quickly, so sound can travel very fast (e.g., ~5,100 m/s in steel).
• In Liquids: Particles are less tightly packed than in solids, so sound moves more slowly (e.g., ~1,480 m/s in water).
• In Gases: Particles are far apart with weak interactions, making it harder for sound to travel quickly (e.g., ~343 m/s in air at 20°C).

Temperature and Density Effects:

In gases, the temperature also affects the speed of sound — warmer gases allow particles to move faster and transmit vibrations more quickly. However, density alone doesn’t determine speed — it’s the ratio of elasticity to inertia (bulk modulus to density) that truly matters.

Practical Examples:

• When you place your ear to a railroad track, you can hear an approaching train long before the sound reaches you through the air — because sound travels faster in metal than in air.
• Ultrasound imaging relies on sound traveling through soft tissues at known speeds to create medical images.

This fundamental concept helps in fields like engineering, medicine, seismology, and acoustics, where understanding how sound behaves in various materials is crucial.