1. How Sound Travels
Sound travels by the transfer of vibrations from one particle to the next. When an object vibrates, it disturbs nearby particles, and this disturbance moves forward as a wave.
The particles themselves do not travel with the wave. They only vibrate around their rest positions.
2. Need for a Medium
Sound requires a material medium (air, water, or solids) to propagate because the vibrations must pass from particle to particle.
In a vacuum, there are no particles to carry the disturbance, so sound cannot travel.
2.1. Why Sound Cannot Travel in Vacuum
Since vibration transfer depends on the presence of particles, the absence of particles in a vacuum means there is nothing to push or pull. Therefore, sound stops completely.
3. Propagation in Different Media
Sound behaves differently depending on the medium it travels through. The arrangement and closeness of particles affect the speed and clarity of sound.
3.1. Propagation in Solids
Particles in solids are tightly packed. This allows vibrations to pass quickly from one particle to another.
3.1.1. Example
Placing an ear on a railway track lets you hear an approaching train earlier because sound moves faster through iron than through air.
3.2. Propagation in Liquids
Particles in liquids are not as close as in solids but are still fairly packed. Sound travels slower than in solids but faster than in gases.
3.2.1. Example
Underwater communication in oceans uses sound waves because they travel well through water.
3.3. Propagation in Gases
Particles in gases are far apart, so it takes longer for vibrations to pass between them. This makes sound slowest in gases.
3.3.1. Example
Talking to someone far away in open air feels delayed compared to listening through a solid surface.
4. Compressions and Rarefactions During Propagation
As sound moves through a medium, it creates regions of high and low pressure:
- Compression: Particles are pushed close together.
- Rarefaction: Particles spread apart.
4.1. How These Regions Travel
The vibrating source produces a repeating pattern of compressions and rarefactions. These move forward as a wave while particles only vibrate locally around their positions.
5. Energy Transfer in Sound
Sound propagation is the transfer of energy, not matter. Each particle transfers energy to the next by pushing and pulling, while staying close to its own place.
5.1. Example to Imagine
Think of a row of people standing in a line. If the first person gently pushes the next, the push reaches the last person, but no one actually moves far from their spot. The energy travels, not the people themselves.