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What is a wave?

We use the word wave in everyday conversation to refer to ocean, light, sound, or earthquake waves. But what do all of these seemingly different phenomena have in common, and why is it important to understand the nature of waves? Let's explore these topics.

Waves transmit the energy that topples buildings during an earthquake, energy that allows us to communicate in the modern world, and energy that allows for life on earth at all. Our observations of the earth from space are also dependent on waves, those that are received by satellites. Thus, waves are a basic feature of the natural world and our ability to understand waves has resulted in many useful devices, cell phones, garage door openers, and microwave ovens, to name a few. With such a variety, what do all waves have in common? Ocean, light, sound, and earthquake waves share the characteristics contained in the scientific definition of wave.

 Definition The Random House dictionary tells us that a wave is: Physics. a progressive disturbance propagated from point to point in a medium or space without progress or advance by the points themselves, as in the transmission of sound or light. It's a wave if: 1) energy moves from one place to another and 2) matter doesn't move from one place to another, for the most part.

For example, ocean waves ceaselessly arrive at the shore without piling up infinite amounts of water. The wave arrives, but the water doesn't.

We know that ocean waves carry energy because they are able to beat up and move objects at the shore. It takes a wave the same amount of energy to move a large boulder as it would for us to do the same, manually or with a bulldozer.

In understanding the earth, it's useful to concentrate on two general classes of waves, mechanical and electromagnetic waves.

Mechanical waves
Common types of mechanical waves include sound or acoustic waves, ocean waves, and earthquake or seismic waves. In order for compressional waves to propagate, there must be a medium, i.e. matter must exist in the intervening space. For our purposes, we use the term matter to mean that atoms must exist in the intervening space. To learn more about different types of mechanical waves such as earthquake waves, link to our module on Mechanical Waves.

Electromagnetic waves
Common types of electromagnetic waves include visible light, infrared, and ultraviolet radiation, among others. The transmission of electromagnetic waves does not require a medium and electromagnetic waves are able to travel through vacuums. Unlike mechanical waves such as sound, electromagnetic waves can travel successfully across the near emptiness of outer space. Thus humanity has been entertained for eons by the stars that light night skies. To learn more about different types of electromagnetic waves such as ultraviolet radiation, link to our module on Electromagnetic Waves.