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# Wave fundamentals

## Waves as vibrations

A wave can be considered as a series of vibrations. A wave is formed from the many vibrations that occur along the path the wave takes.

An ocean wave causes an alternating rise-and-fall of the surface of the ocean.

The vibrations of a wave do not remain at a particular position; they move with a fixed direction. This means that waves move with time.

A wave transfers energy between two points without transferring matter. This means that the particles within a wave which move back-and-forth are not permanently moved to another location.

Other examples of waves include:

• Sound waves
• Light waves
• Waves on a guitar string
Ocean waves

## Waves as oscillations

A wave can be understood as a chain of oscillations.

A sound wave travelling through air involves multiple air particles oscillating at the same time and these oscillations follow a particular pattern (i.e. they do not all reach maximum displacement at the same time).

Ocean waves, sound waves and electromagnetic waves (such as light) share many similarities in behaviour. Most important among these are some of the patterns of interference (e.g. the interference of two ocean waves coming from different directions).

An important differentiation is made between:

• mechanical waves which involve oscillations of particles such as water molecules and
• electromagnetic waves which do not require particles to carry them.

Waves are produced by different types of sources (e.g. guitar strings, vibrating dippers, seismic tremors), each producing waves with a particular waveform.

A particle at a particular position along the wave oscillates in place as the wave moves from left to right.

## Waves and other disturbances

A wave is a disturbance (or a series of disturbances) that travels through space without the permanent movement of matter.

A stone dropped into a pool of water creates ripples (a series of disturbances) that travel outwards from the point that the stone was dropped.

Waves are not the only type of disturbance. Disturbances that do not travel are not waves.

Oscillations, like the swinging of a pendulum or the swinging of a mass suspended on a spring, are not waves.

Disturbances that cause the permanent movement of matter are also not waves.

The explosion of gunpowder in a gun "disturbs" a bullet. The bullet is fired from the gun (permanently displaced).

Ripples in a pool of water.

## Crests and troughs

A crest is a point on a wave with the highest possible value or upward displacement.

A trough is the opposite of a crest. It is the point on a wave with the lowest possible value.

Surfers try to ride the crests of water waves in the sea.

A wavefront is an imaginary line at right angles to the direction the wave travels. Every point on a wavefront has travelled the same distance from the source of the wave.

Dropping a stone into some water creates ripples. These are the wavefronts of the wave.

A wave moving from right to left