Know that, in general, sound travels faster in solids than in liquids and faster in liquids than in gases

3.4 Sound

Speed of Sound in Different Media

Sound travels as a pressure wave through a medium. The speed at which it moves depends mainly on how tightly packed the particles are and how stiff the medium is. In general:

• Solids ➜ fastest
• Liquids ➜ medium speed
• Gases ➜ slowest

Why Does This Happen?

The speed of sound is given by the equation:

\$v = \sqrt{\dfrac{B}{\rho}}\$

where \$B\$ is the bulk modulus (stiffness) and \$\rho\$ is the density. Solids have a high bulk modulus and relatively low density, giving a high speed. Gases have a low bulk modulus and low density, resulting in a lower speed.

Typical Speeds (at 20 °C)

Analogy: The Marching Band

Imagine a marching band moving through three different places:

1. In a solid hallway (like a steel bridge). The band can move quickly because the floor is rigid and the band members are tightly packed.
2. In a water pool (like a swimming pool). The band moves slower because the water is less rigid, but still faster than in air.
3. In an open field (like the air). The band moves the slowest because the air offers the least resistance.

Just as the band’s speed changes, so does the speed of sound in different media.

Key Takeaway

Sound travels fastest in solids, slower in liquids, and slowest in gases. This order is due to the increasing stiffness and decreasing density from solids to gases.