How Do Sound Waves Differ Between Solids, Liquids, and Gases?

A sound wave is a mechanical wave, meaning it requires a medium (a substance) to travel. It propagates by causing vibrations in the particles of that medium. The primary differences in how sound travels through solids, liquids, and gases are due to the spacing of the particles and the strength of the bonds between them.

1. Sound in Solids

• Particle Structure: Particles are tightly packed in a fixed, rigid lattice. They are strongly bonded to each other.
• Wave Propagation: When one particle vibrates, it immediately and forcefully collides with its neighbor. This creates a very rapid and efficient transfer of energy.
• Speed: Sound travels fastest in solids. The strong bonds and close packing (high elasticity) allow vibrations to pass through almost instantly. (e.g., ~5,120 m/s in steel).
• Efficiency: Sound travels very efficiently with low energy loss (low attenuation). This is why you can hear a train from far away by putting your ear to the rail.
• Wave Type: Solids can transmit both longitudinal (compression) waves and transverse (shear) waves because the rigid bonds can resist both types of motion.

2. Sound in Liquids

• Particle Structure: Particles are close together but are not in fixed positions; they can slide past one another.
• Wave Propagation: The vibration is passed along as a longitudinal (compression) wave, similar to in gases but more effective due to the proximity of particles.
• Speed: Sound travels slower than in solids but faster than in gases. The particles are much closer than in a gas, but the bonds are weaker than in a solid. (e.g., ~1,480 m/s in water).
• Efficiency: More efficient than gases but less efficient than solids.
• Wave Type: Liquids can generally only transmit longitudinal waves, as they do not have the strong "shear" resistance needed for transverse waves.

3. Sound in Gases (e.g., Air)

• Particle Structure: Particles are very far apart and move randomly with weak bonds between them.
• Wave Propagation: Sound travels as a longitudinal (compression) wave. A vibrating object pushes a group of particles, which then travels to push the next group. This process is relatively slow due to the large empty space between particles.
• Speed: Sound travels slowest in gases. A lot of time is lost as particles travel across the gaps to collide with their neighbors. (e.g., ~343 m/s in air at 20°C).
• Efficiency: This is the least efficient medium. Sound waves lose energy quickly (high attenuation) and disperse into the wide-open space.
• Wave Type: Gases can only transmit longitudinal waves.