Concepts

# Wave

The word “wave”, from the point of view of physics , is used to designate the transmission of energy without displacement of matter. It is a disturbance or agitation that moves in a certain environment and that, after passing, leaves it in its initial state. This mechanism covers a wide range of situations: From waves on the surface of a liquid to light, which is itself a type of wave.

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The transport of energy without matter is a common physical phenomenon . Imagine a pond on a sunny, windless day. The surface of the water is perfectly smooth. Now imagine someone throwing a stone: At the point of impact, we immediately see ripples appear that seem to move away from the center in concentric circles . After a few moments, the pond is smooth and still again.

### When throwing a stone into a pond, what happens?

The thrown stone created a disturbance in the water and the latter absorbs some of the stone’s energy . The disturbance spreads around the point of impact. The water moves up and down creating a ripple which in turn will create other ripples. This means that a part of the energy is transferred from one ripple to the next.

Once the energy of the stone has dispersed from wave to wave, the surface of the water returns to its initial state. The height, distance and duration of the waves depend on the energy supplied initially, in other words, on the mass of the stone and the force with which it was thrown.

These oscillations on the water surface allow the waves to be “seen” in the simplest and most direct way. However, there are many other types of wave that follow the same principle but are not visible to the naked eye.

### Types of waves

• Mechanical and acoustic

Simply tapping a finger on the corner of a table creates mechanical waves that travel through the air (the percussion sound) and across the table (in the form of vibration). Waves are another example, from ripples in a pond to a tidal wave. Seismic waves belong to this category, they are the consequence of deep geological shocks and propagate through the earth’s crust.

• From electromagnetic fields

Electromagnetic waves (also known as electromagnetic fields or EMFs) are an equally varied category, which can be classified by frequency bands (known as the electromagnetic “spectrum”). This spectrum ranges from the lowest frequencies (for example, those of power lines) to the highest frequencies (UV rays, X-rays, gamma rays). Between these two extremes are the radio waves (or radio frequencies) present and used in communications and, of course, light: Everything that our eyes see is transmitted by electromagnetic fields, whose frequency corresponds to the “visible” band of the spectrum.

• Ionizing and non-ionizing

The frequency of a wave also reflects the amount of energy it can carry. At very high frequencies, that is, well above the visible spectrum, the amount of energy is so great that it can modify the structure of the matter it passes through, for example, altering a molecule , freeing an electron from an atom and transforming it into a ion.

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