Waves are made of vibrations which transfer energy from one place to another. However, no matter, so no solid, liquid or gas, is transferred.

Some waves have to travel through a substance. This is known as a medium and can be a solid, liquid or gas. For example, sound waves and seismic waves need to travel through a medium and it’s this medium that vibrates as the wave travels through it.

Other waves don’t require a medium. They can travel through one but it’s not necessary. For example, electromagnetic waves like infra red rays, visible light and microwaves. These waves are able to travel through empty space and it’s the electrical and magnetic fields which vibrate as the wave travels.

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Transverse waves

With transverse waves the oscillations (another terms for vibrations) are at right angles to the direction of travel and energy transfer.

Examples of transverse waves include:

• – light
• – Electromagnetic radiation
• – Water waves
• – S waves (a type of seismic wave)

When electromagnetic waves travel through a vacuum, like space, they move at a constant speed.

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Longitudinal waves

With longitudinal waves the oscillations move in the same direction as the direction of travel and energy transfer.

Examples of longitudinal waves include:

• – sound waves
• – waves in a stretched spring
• – P waves (a type of seismic wave which travels through solids and liquids)

The pattern formed by longitudinal waves includes areas of rarefaction and compression:

• – rarefaction areas are regions in which the waves are far apart
• – compression areas are regions in which the waves are close together