wave is a perturbation that propagates in space and which can transport energy from one point to another. This perturbation consists of the variation of any physical quantity (for example pressure variation, temperature, electric field strength, position, etc.).

Many natural phenomena are described in terms of waves. The waves in the water are together the prototype of the wave and a rather particular case, as they are waves that mainly affect the surface of separation between two means (air and water), and therefore have less general characteristics of the waves traveling in a homogeneous medium (see transversal and longitudinal waves). The question of the nature of light is a typical example of a more difficult case to decide. Opposing theories in support of the corpuscular and wave-like nature of light have followed one another since antiquity, and found an original solution in contemporary physics, according to which both radiation and matter possess traits common to particles and waves when they are observed at a microscopic level (see waveband).

In the case of electromagnetic waves, due to the complexity of their interaction with matter, waves of the same physical nature can have very different effects depending on their frequency, varying from the radio waves used in telecommunications, to visible light, dangerous ionizing radiation such as x-rays and gamma rays.

The sound waves, as well as one of the physiological means of human communication, are actually a particular type of mechanical waves to which the whole section is dedicated, the sound and its perception.

The mechanical waves, moreover, concern many aspects of our daily life, from the most obvious on a small scale concerning oscillations and vibrations (see resonance phenomena in mechanical systems), to those less evident, but not less important on a large scale, such as the planetary waves, which occur in the fluids of the ocean and the atmosphere due to the rotation of the earth.

If the mode of propagation of a wave in a certain medium is known, the wave itself becomes a powerful tool for investigating the properties of that medium. For example, measuring the properties of seismic waves such as amplitude, the direction of oscillation, arrival times to the seismograph not only indicates where the epicenter of an earthquake is located but can give valuable information about the internal structure of the earth.

Most of the properties of matter at the molecular or atomic level are measured by irradiating a sample with waves (usually electromagnetic such as visible light, ultraviolet, X-rays, gamma rays, but also electron or neutron beams), and observing the sample reaction. The same principle underlies many modern diagnostic techniques in medicine: X-rays (X-ray) or ultrasound are used to “see” parts of the body that are not visible from the outside with normal visible light. The science of conservation and restoration of works of art also uses techniques based on the use of appropriate spectroscopies (fluorescence, absorption, transmission in the optical, infrared, ultraviolet, X bands).

Scientific investigations are nowadays a fundamental tool for law enforcement and based on a set of physico-chemical-biological investigation techniques they allow to acquire elements to reconstruct a crime scene that are often crucial for the investigation. Again the use of electromagnetic waves of various types to detect the presence of various types of traces, or to analyze them has now become common practice.

Often illuminating certain substances with waves of a certain type are highlighted aspects that otherwise remain hidden: in mineralogy it is common practice to use the light of Wood (ultraviolet) to verify the luminescence of minerals, and the police departments use similar methods to highlight traces otherwise invisible organic at the scene of a crime.

Measuring the change in direction of a light wave when it passes from the air to the glass tells us the value of the refractive index of the glass compared to that of the air (see the refraction section), but in general, the color or the transparency, reflectivity, and all the optical properties of a material are the results of the interaction (which can be very complex) of that material with electromagnetic waves.

Observing how a wave is reflected or transmitted at the interface between two different substances indicates directly how much the media is opposed to the transmission of energy by the wave itself (see the refraction section in one dimension), and allows us to optimize the ‘coupling between different media (such as a HiFi amplifier and microphone, or speakers), to get maximum efficiency

The waves allow us to study distant phenomena in space and time: astronomy and astrophysics base their observations on the study of the spectrum of electromagnetic radiation from celestial bodies, from interstellar matter, and from deep space. The radiations studied occupy the whole spectrum of electromagnetic waves, and come from such distances that their origin can go back to remote times as the first moments of life in the universe. In addition, frequency shifts by Doppler effect give us information on the evolution of the universe.

Finally, the general theory of relativity predicts that gravitational waves consisting of a fluctuation in the spacetime curvature can be generated in certain cases (as in a binary system, or in the explosion of a supernova) and propagate in space-time. The waves carry energy and momentum. In this case we speak of radiant energy, or radiation. A wide range of applications allows the transport and use of energy by means of waves, from lasers to microwaves, to be more efficient. However, the first and simplest device to irradiate and direct the energy produced by a source is the antenna.

Transmitted energy can become information, and waves become the most effective and rapid means of communication. Waves lend themselves to transmitting information through a modulation of their properties. In fact, for example, communications in amplitude modulation (AM), frequency (FM), phase (PM), etc. are distinguished in radio communications. Sound waves are the natural means of vocal communication, while electromagnetic waves are the main means of communication at a distance of our planet.

Much of the science of telecommunications has been devoted to the problem of how to generate signals suitable for the transmission of different types of information, and transmit them to the maximum possible distance while minimizing noise in the transmission channel. A good deal of analogue and digital electronics deals with the generation, conditioning, transmission and reception of the signal.

Acoustic wave (sound wave)

Acoustic waves (also known as sound waves) are a type of longitudinal waves that propagate by means of adiabatic compression and decompression.

Longitudinal sound waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle velocity, particle displacement, and sound intensity.

Acoustic waves travel with the speed of sound which depends on the medium they’re passing through.

Mechanical wave energy

Mechanical wave energy is kinetic and potential energy in an elastic material (medium) due to a propagated deformational wave (oscillation of matter). Mechanical waves transport energy. This energy propagates in the same direction as the wave. Examples: ocean wind-generated waves, sound waves, seismic waves.

Any kind of wave (mechanical or electromagnetic) has a certain energy. Mechanical waves can be produced only in media which possess elasticity and inertia. A mechanical wave requires initial energy input. Once this initial energy is added, the wave travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can still travel through one. One important property of mechanical waves is that their amplitudes are measured unusually, displacement divided by (reduced) wavelength.

When this gets comparable to unity, significant nonlinear effects such as harmonic generation may occur, and, if large enough, may result in chaotic effects. For example, waves on the surface of a body of water break when this dimensionless amplitude exceeds 1, resulting in foam on the surface and turbulent mixing. Some of the most common examples of mechanical waves are water waves, sound waves, and seismic waves. There are three types of mechanical waves: transverse waves, longitudinal waves, and surface waves.

  1. Transverse waves cause the medium to vibrate at a right angle to the direction of the wave, or energy being carried by the medium. In other words: a transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave). Transverse waves have two parts—the crest and the trough. The crest is the highest point of the wave, and the trough is the lowest. The distance between a subsequent crest and a trough is half of the wavelength. The wavelength is the distance from crest to crest or from trough to trough.
  2. Longitudinal waves cause the medium to vibrate parallel to the direction of the wave. It consists of multiple compressions and rarefactions. The rarefaction is the farthest distance apart in the longitudinal wave, and the compression is the closest distance together. In other words: longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave. Mechanical longitudinal waves are also called compressional or compression waves, because they produce compression and rarefaction when traveling through a medium, and pressure waves, because they produce increases and decreases in pressure. The speed of the longitudinal wave is increased in the higher index of refraction, due to the closer proximity of the atoms in the medium that is being compressed. The sound is considered a longitudinal wave.
  3. Surface waves travel along a surface that is between two media. An example of a surface wave would be waved in a pool, or in an ocean, lake, or any other type of water body. In seismology, several types of surface waves are encountered. Surface waves, in this mechanical sense, are commonly known as either Love waves (L waves) or Rayleigh waves.

Wave interference

Wave interference is a phenomenon that occurs when two waves meet while traveling along with the same medium, in which the two waves superpose to form a resultant wave of greater, lower, or the same amplitude. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.