How Sound Travels Through Matter
When a guitar string vibrates, the movement reaches your ears even though the string never touches them. Sound carries energy through a material as nearby particles push and pull on one another. It needs matter to travel, which is why an empty vacuum cannot carry ordinary sound.
A vibration creates a pressure wave
A vibrating object moves the particles beside it. When a loudspeaker cone moves forward, it crowds nearby air particles together, creating a compression. When it moves backward, it leaves a region where particles are more spread out, called a rarefaction.
These compressions and rarefactions travel outward as a longitudinal wave. The air particles move back and forth around their usual positions, while the disturbance and energy move through the room. The particles do not travel all the way from the speaker to your ear.
When the wave reaches the ear, it makes the eardrum vibrate. Tiny bones transfer the movement into the inner ear, where specialised cells help turn it into electrical signals for the brain. Hearing depends on both the physical wave and the biological system that detects it.
Frequency and amplitude change the sound
Frequency is the number of complete vibrations each second and is measured in hertz. A higher frequency is usually heard as a higher pitch, while a lower frequency produces a lower pitch. Human hearing covers only part of the full range of possible sound frequencies.
Amplitude describes the size of the vibration. A wave with greater amplitude usually sounds louder because it transfers more energy. Loudness also depends on distance, the surroundings and how sensitive the listener's ear is.
Pitch and loudness are different properties. A note can be high and quiet or low and loud. Keeping frequency separate from amplitude prevents two common ideas from becoming tangled simply because both are drawn as waves.
Sound travels differently in each material
Sound usually travels faster in solids than in liquids and faster in liquids than in gases. Particles in solids are close together and strongly connected, so vibrations can be passed along quickly. The exact speed depends on the material's stiffness, density and temperature.
Sound can reflect from a surface to create an echo. It can also be absorbed, transmitted or scattered. Soft porous materials often reduce reflections, while hard smooth surfaces produce clearer echoes. These effects shape the acoustics of rooms and halls.
Remember the basic pattern:
- •A source begins by vibrating.
- •Particles oscillate around fixed positions.
- •Compressions and rarefactions carry energy.
- •Frequency affects pitch.
- •Amplitude affects loudness.
The takeaway
Sound is a mechanical wave that transfers energy through vibrating particles. Frequency helps determine pitch, amplitude affects loudness and the material changes the speed and path. Picture particles passing a disturbance to their neighbours, and sound becomes easier to understand than the misleading idea of air carrying tiny pieces of music.