Speeding sound

In this chapter

The 'speed' of a sound wave refers to how fast the disturbance is passed from particle to particle
Sound travels at different speeds depending on what it is travelling through
Sound waves travel slowest through gases, faster through liquids, and fastest through solids
The temperature and other properties of the medium determine how fast the sound moves
The sound barrier was once believed to be a physical barrier preventing large objects from travelling faster than sound, but is has been broken by aeroplanes and other vehicles

Introduction

As we know, a sound wave is a pressure disturbance which travels through a medium by means of particle interaction. As with any wave, the 'speed' of a sound wave refers to how fast the disturbance is passed from particle to particle.

Sound travels at different speeds depending on what it is travelling through. Sound waves travel the slowest through gases, faster through liquids, and fastest through solids. The temperature of the medium also affects the speed of sound.

Gases

The speed of sound in a gas depends on the type and temperature of the gas. The relative humidity of air also has a slight effect on the speed of sound. At 20^oC, or room temperature, sound travels at approximately 343 meters per second. This speed will differ based on the type of gas or composition of air and the temperature of the medium.

Liquids

The molecules in a liquid are more tightly packed than in a gas, therefore sound can travel faster in liquids than in gases. In fresh water, sound waves travel at around 1435 metres per second -; over four times faster than in air. In salt water, sound travels at around 1500 metres per second. The speed of sound in seawater depends on several factors: temperature, pressure (caused by depth) and salinity (how salty it is).

Marine animals like whales and dolphins use sound waves to communicate with other animals and to locate food and other objects. This method of communication is particularly effective over long distances because sound travels much faster in water.

See Image 1

Solids

Sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or a gas. This allows sound waves to travel more quickly through solids. Sound waves travel over 17 times faster through steel than through air. The speed of sound in steel is 5960 meters per second. This is not a universal rule, however, as sound can travel faster in some liquids than in some solids.

See video Speeding sound

The sound barrier

The sound barrier was once believed to be a physical barrier preventing large objects from travelling faster than sound. Jet aeroplanes (including the commercial Concorde, now no longer in service), however, can travel faster than the speed of sound (a land vehicle also broke the sound barrier in 1997). 'Breaking' the sound barrier is the term given to the transition from subsonic (slower than the speed of sound) to supersonic (faster than the speed of sound) travel. As a plane breaks the sound barrier, a sonic boom is heard -; this is the audible component of a shock wave that travels through air. Also, a condensation cloud can be seen to form when a jet breaks the sound barrier. This is due to the sudden drop in air pressure.

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