Explanation:
While all waves adhere to the principle of “transport of energy without moving matter”, wave forms consitiute a vast family of forms within which one can ideintify types with varied physical properties.
Specifically, there are two broad classes of waves: mechanical waves which must pass through physical matter in order to propagate, and electromagnetic waves which need not to do so.
Mechanical and acoustic waves
Simply tapping a finger on the corner of a table creates mechanical waves that spread in the air (the sound of tapping) and in the table (as vibrations. Water waves are another example – from the ripples on a pond up to a tidal wave. Seismic waves belong to this category: they are created by deep geological shocks and propagate through the Earth’s crust.
At the other end of the scale, plucking on a stretched rubber band makes it vibrate, generating mechanical waves that move through the rubber.
Sound is even more universal: it is a wave generated by the mechanical vibration of a material and moves through air or water. These so-called acoustic waves are particularly easy to use and adjust or ‘modulate’: if speak in one direction or another, shout or whisper – each such change will alter the wave length, amplitude and frequency of the sound.
Electromagnetic fields
Electromagnetic waves (also known as Electromagnetic fields or EMF) form an equally varied category, which can be classified by frequency bands: this is known as the electromagnetic “spectrum”. It extends from the lowest frequencies (those of power lines, for example) to the highest frequencies (UV, X-rays, gamma rays). In between are radio waves (or radio frequencies), found naturally and used in communications and of course, light. Everything our eyes see is transmitted by EMFs the frequency – or colour – of which corresponds to the “visible” band of the spectrum. What then distinguishes EMFs from acoustic waves? They, EMFs, do not require any medium to move at very high speeds over vast distances (like starlight), or to travel through empty space or pass through specific materials.
