### KS3 Physics

Energy
Motion and Forces
Waves
Electricity and Electromagnetism
Matter
Space Physics

# Sound Waves

When an object vibrates, it produces sound. Sound can only travel through a medium, such as a solid, liquid or gas.

Sound waves are longitudinal, meaning the vibrations occur parallel to the direction of wave travel. This is why sound waves show periods of compression and rarefaction.

## Sound Travel

Loudspeakers work by converting electrical energy into kinetic energy.

When the speaker produces sound:

1. The speaker diaphragm oscillates (moves back and forth)

2. The oscillation causes movement in the surrounding air molecules

3. As the air molecules oscillate, energy is transferred to the surrounding air molecules

The periods of compression and rarefaction transfer energy through the air.

## The Speed of Sound

Sound travels at different speeds, depending on the medium. Even though sound travels very fast, its speed over a given distance can be measured in metres per second (m/s).

• The speed of sound in air is around 343 m/s
• Sound travels almost five times faster in liquids than in air – For example, the speed of sound in water is 1,481 m/s
• The speed of sound in solids is around 6000 m/s – Sound travels the fastest in solids

Sound travels faster through mediums where particles are closer together. As you can see in the list above, sound travels fastest in solids, then liquids and then slowest in gases. This is because the particles of solids are closest together, then liquids and then furthest apart in gases.

When sound travels in a solid, the particles are very close together. So as they collide, they can transfer energy much quicker than other mediums.

## Sound in Space

Because sound waves rely on the vibrations of particles, there is no sound in space where particles are absent.

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