Q1.
How does sound reach your ear from the source? Sound travels through air but does it also travel through solids and liquids?
Answer
Sound reaches the ear through a material medium, and yes — it travels through solids and liquids as well as gases.
The source sets the particles next to it oscillating. Those particles collide with their neighbours and pass on the compression; the neighbours pass it on further; and so the disturbance is relayed, particle to particle, all the way to the eardrum. The material that does this relaying is called the medium.
- Solid: Activity 10.3 — a scratch on a desk is heard much more clearly with the ear pressed on the desk than through the air.
- Liquid: Activity 10.4 — two spoons tapped under water are still heard.
- Gas: ordinary hearing through air.
Why solids carry sound best: in a solid the particles are packed close together and are strongly bonded, so a push is handed on to the next particle almost immediately. In a gas the particles are far apart and must travel some distance before colliding, so the disturbance creeps along. That is why sound is fastest in solids (steel ≈ 5000 m s⁻¹), slower in liquids (water ≈ 1500 m s⁻¹) and slowest in gases (air ≈ 340 m s⁻¹).