Degenerate matter

Degenerate matter is a highly dense state of fermionic matter in which particles must occupy high states of kinetic energy in order to satisfy the Pauli exclusion principle. Under extremely high pressure, as in the cores of dead stars, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter, which […]

Quark matter (QCD)

Quark matter or QCD matter refers to any of a number of theorized states of matter whose degrees of freedom include quarks and gluons. In regular cold matter, quarks, fundamental particles of nuclear matter, are confined by the strong force into hadrons that consist of 2-4 quarks, such as protons and neutrons. Quark matter or quantum chromodynanamical (QCD) matter is […]

Thermal energy

It is called thermal energy that type of energy that anybody has at a temperature above zero. This condition represents an extensive quantity and is directly proportional to the temperature that the body generates. Thermal energy is the kinetic energy of the microscopic motion of particles, a form of a disordered equivalent of mechanical energy; […]

Rest energy

The rest energy E0 of a particle is defined as E0 = m0c2 where “c” is the speed of light in vacuum. In general, only differences in energy have physical significance. The concept of rest energy follows from the special theory of relativity that leads to Einstein’s famous conclusion about the equivalence of energy and mass. On the other […]

Radiant energy

Radiant energy is the potential energy stored in the fields of propagated by electromagnetic radiation (such as light, X-rays, gamma rays, and thermal radiation) which may be described in terms of either discrete packets of energy, called photons, or continuous electromagnetic waves. Radiant Energy to electricity Solar energy can be used to produce electricity. Two ways […]

Wind wave energy

Wind waves energy has a certain amount of randomness: subsequent waves differ in height, duration, and shape with limited predictability. They can be described as a stochastic process, in combination with the physics governing their generation, growth, propagation, and decay—as well as regulating the interdependence between flow quantities such as the water surface movements, flow velocities, and […]

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.

Mechanical energy

Mechanical energy is the sum of macroscopic translational and rotational kinetic and potential energies. Mechanical energy is the energy that is possessed by an object due to its motion or due to its position; can be either kinetic energy (energy of motion) or potential energy (stored energy of position). Objects have mechanical energy if they are in […]

Magnetic energy

Magnetic energy is the potential energy due to or stored in magnetic fields. Magnetic energy and electric energy are related to Maxwell’s equations. In fact, thanks to Maxwell’s work, magnetic and electric energy are more appropriately considered as a single force. Together, they are what is known as electromagnetic energy (a form of energy that has […]

Internal energy

Internal energy is a property of a thermodynamic system. In an ideal gas, the internal energy is the statistical mean of the gas particles’ kinetic energy, and it is this kinetic motion that is the source and the effect of the transfer of heat across a system’s boundary. For this reason, the term “thermal energy” is […]

Gravitational energy

Gravitational energy is the potential energy a body with mass has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field. Gravitational energy is dependent on the masses of two bodies, their distance apart, and the gravitational constant G. The general expression for gravitational potential energy arises from the law of […]

Electric energy

Electric energy is the energy newly derived from electric potential energy or kinetic energy due to or stored in charged particles within an electric field. When loosely used to describe energy absorbed or delivered by an electrical circuit (for example, one provided by an electric power utility) “electrical energy” talks about energy which has been converted […]

Baryonic matter

By definition, baryonic matter should only include matter composed of baryons. In other words, it should include protons, neutrons and all the objects composed of them (i.e. atomic nuclei), but exclude things such as electrons and neutrinos which are actually leptons. The name “baryon”, introduced by Abraham Pais, comes from the Greek word for “heavy” […]

Dark energy

Dark energy is a form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. It has been hypothesised to account for the observational properties of distant type Ia supernovae, which show the universe going through an accelerated period of expansion. Like dark matter, dark energy is not directly observed, but […]


Superfluidity is a special quantum state of matter in which a substance (called superfluid) flows with zero viscosity (without loss of kinetic energy), by the absence of entropy and by having infinite thermal conductivity. The superfluids, if placed in a closed path, can flow infinitely without friction.


Superfluids have many unusual properties. They behave like typical components of solutions, with all the properties associated with normal fluid and superfluid components. Therefore it is impossible to set a temperature gradient in a superfluid, as it is impossible to set a potential difference in a superconductor. Superfluidity was discovered by Pëtr Leonidovič Kapica, John […]


In Physics, a fluid is a substance that continually deforms (flows and cannot resist deformation) under applied shear stress or external force. Fluids include gases, liquids, and plasma. All fluids are compressible (that is, their density increases under increasing pressure) to some extent, but liquids are much less compressible than gases and are generally considered incompressible. Even gases may […]

Thermodynamic temperature (kelvin)

The definition of the unit of thermodynamic temperature was given in substance by the 10th CGPM (1954) which selected the triple point of water as the fundamental fixed point and assigned to it the temperature 273.16 K, so defining the unit. The 13th CGPM (1967/68) adopted the name kelvin, symbol K, instead of “degree Kelvin,” symbol °K, […]

Curie temperature (or Curie point)

The Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism.


Temperature gradient. Critical temperature.


Heat transfer. Heat flux. Heat capacity. Latent heat of fusion. Latent heat of condensation. Latent heat of sublimation. Latent heat of vaporization.


Sound pressure (acoustic pressure). Sound intensity. Sound propagation speed. Infrasound. Ultrasound (ultrasonics). Soundproofing.


Friction coefficient. Static friction. Kinetic or dynamic friction. Sliding friction. Rolling friction.


Antiferromagnetism is a characteristic property of some materials such as manganese, chromium, hematite, oxides MnO2, FeO, CoO, etc. (called antiferromagnetic materials); in these materials, contrary to what happens for ferromagnetic materials (in which the configuration of minimum energy occurs for parallel spins), the interaction between the atoms is such as to create a configuration of minimum energy when […]


Ferrimagnetism is a type of permanent magnetism that occurs in some crystals when the magnetic moments of nearby ions tend to align antiparallel: it is, therefore, a type of antiferromagnetism; this situation occurs mainly in compounds known as ferrites. The term ferrimagnetism was originally proposed by Néel to describe the magnetic ordering phenomena in ferrites, in which iron […]


Ferromagnetism is the property of some materials, called ferromagnetic materials, to magnetize very intensely under the action of an external magnetic field and to remain magnetized for a long time when the field is canceled, thus becoming magnets. This property is maintained only below a certain temperature, called Curie temperature, above which the material behaves like […]


A magnet is a material or object that produces a magnetic field. The name derives from the Greek μαγνήτης λίθος (magnétes líthos), that is “Magnesia stone,“ from the name of a place in Asia Minor, known since ancient times for the huge deposits of magnetite. A permanent magnet is an object made from a material that is […]


Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. Paramagnetic materials are characterized at the atomic level by magnetic dipoles that align with the applied magnetic field, being weakly attracted to it.


Diamagnetism is a form of magnetism that some materials show in the presence of a magnetic field. Diamagnetic materials are characterized by the fact that magnetization has the opposite direction with respect to the magnetic field; therefore these materials are weakly “rejected.“ This is a very weak quantum effect, which is voided if the material has […]

Nuclear force

Strong nuclear interaction, has a property called color charge, holds quarks together, elementary constituents of protons and neutrons, and also the latter within the nucleus. It is absolutely the most intense force among those known so far, to the point that it is not possible at low energy to isolate and separate a single quark from […]

Weak interaction

The weak interaction, which is also often called the weak force or weak nuclear force, is responsible for some nuclear phenomena such as beta decay of the atomic nuclei associated with radioactivity and acts between leptons and quarks (semileptonic interactions), between only leptons (leptonic interactions) and between only quarks (non-leptonic interactions) through the exchange of massive vector bosons […]


Piezoelectricity, also called the piezoelectric effect, is the property of some crystalline materials to polarize generating a voltage when they are subject to mechanical deformation (direct piezoelectric effect) and at the same time to deform in an elastic way when subjected to a voltage (reverse piezoelectric effect or Lippmann effect); the sign of polarization reverses depending on […]

Relative motion

Relative motion is the study of the motion of an object with regard to some other moving object. Thus, the motion is not calculated with reference to the earth but is the velocity of the object in reference to the other moving object as if it were in a static state. Normally the reference system used […]


Law of conservation of energy. Energy sources. Renewable energy. Non-renewable energy. Chemical energy. Elastic energy. Electric energy. Gravitational energy. Internal energy. Magnetic energy. Mechanical energy. Principle of the conservation of mechanical energy. Mechanical wave energy. Nuclear potential energy. Kinetic energy. Potential energy. Nuclear potential energy. Quantum chromodynamics binding energy. Radiant energy. Rest energy. Soundwave energy. Thermal energy. Wind wave energy. Energy harvesting. Unconventional energy.

Quantum chromodynamics binding energy

Quantum chromodynamics binding energy (QCD binding energy), gluon binding energy or chromodynamic binding energy is the energy binding quarks together into hadrons. It is the energy of the field of the strong force, which is mediated by gluons. QCD binding energy contributes most of the hadron’s mass. Most of the mass of hadrons is actually QCD binding energy, […]

Kinetic energy

Kinetic energy is the energy of motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body […]

Elastic energy

Elastic energy is potential energy related to elastic force, stored in the deformation of a material (compression or stretching) or a physical system (distortion of volume or shape) exhibiting a restorative force. This also means that elastic potential energy is zero in objects that have not been stretched or compressed. The elastic potential energy equation is […]


Translation; Rotation; Rototranslation; Plane motion; Uniform motion; Uniform straight motion; Smoothly accelerated motion; Relative motion; Cyclical motion; Circular motion; Steady motion; Transient motion; Anharmonic motion.


The force may be thought of as an influence which tends to change the motion of an object. Forces are inherently vector quantities, requiring vector addition to combine them. The SI unit for force is the newton [N], which is defined by Newton = kg·m/s2 as may be seen from Newton’s second law. In mechanics, forces are seen as the causes of […]


To accelerate means to speed up. The greater the acceleration, the greater the change in velocity over a given time. The average acceleration is the rate at which velocity changes: \[a_{avg}=\dfrac{\Delta v}{\Delta t}=\dfrac{v_f-v_0}{t_f-t_0}\] where \(v\) is velocity, and \(t\) is time. Acceleration is a vector in the same direction as the change in velocity, \(\Delta v\). Since velocity […]


Infrared radiation. Infrared spectroscopy. Infrared astronomy.


Acoustic impedance. Electrical impedance. How to calculate electrical impedance. Mechanical impedance. Wave impedance.

Quantum spin liquid (QSL)

The quantum spin liquid is a state of matter that can be achieved in a system of interacting quantum spins. The word “liquid“ refers to a disordered state in comparison to a ferromagnetic spin state (as much in the way liquid water is in a disordered state compared to crystalline ice). However, unlike other disordered states, a quantum spin […]


A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term “laser“ originated as an acronym for “light amplification by stimulated emission of radiation“. The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by […]


Humidity is the amount of water vapor in the air, measured as mass of water per unit volume or mass of air, or as a percentage of the maximum amount the air would support without condensation, or indirectly via the dew point. Saturation of the air occurs when the water vapor pressure reaches the vapor pressure […]


The potential energy, stored in the form of an electric charge imbalance and capable of provoking electrons to flow through a conductor, can be expressed as a term called voltage (or electric potential difference, electric pressure, and electric tension), which technically is a measure of potential energy per unit charge of electrons or something a physicist would call […]

Pyroelectricity (pyroelectric effect)

Pyroelectricity is a property of certain materials (especially crystals which are naturally electrically polarized) to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage […]

Triboelectric effect

The triboelectric effect (also known as triboelectric charging) is a type of contact electrification in which certain materials become electrically charged after they come into frictional contact with a different material, and are then separated. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties. It is […]


Parallax is a deceptive change in the relative position of an object with a change in the position of the observer. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances. Parallax error The parallax error is due to the fact that the […]


Inertia is the resistance, of any physical object, to any change in its velocity. This includes changes to the object’s speed or direction of motion. The principle of inertia No force is required to maintain motion with constant velocity in a straight line, and absolute motion does not cause any observable physical effects.


Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. This definition can be stated for the generic point of any stressed surface (not necessarily flat but without angular points): considering a surface element small enough to be considered flat (as it can be confused […]


Density of a mixture. Relative density (specific gravity).


In geology, a rheid is a substance whose temperature is below the melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude \((10^3)\) greater than the elastic deformation under the given conditions. A material is a rheid by virtue of the time of observation. The term, coined […]


Viscoelasticity is the study of materials which have a time-dependent strain that exhibit both viscous and elastic characteristics when undergoing deformation. Viscoelastic response is often used as a probe in polymer science, since it is sensitive to the material’s chemistry and microstructure. The identification of the viscoelastic behavior is carried out by measuring the variation in viscosity \((\mu)\) […]


Anelasticity is a characteristic of viscoelastic materials that depends on some physical properties of the material itself. Anelasticity is the opposite of elasticity. An anelastic material subjected to stress undergoes deformations that are not proportional to the stresses and that do not disappear when the force is zeroed. In other words, an anelastic material will fully […]


Elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate forces are applied to them. If the material is elastic, the object will return to its initial shape and size when these […]


Buoyancy or upthrust is an upward force exerted by a fluid that opposes the weight of an immersed object; it is what makes an object float, sink, or remain neutrally buoyant in the water (or other fluids). The symbol for the magnitude of buoyancy is \(B\) or \(F_B\). As a vector, it must be stated with both magnitude […]


The candela (cd) is the base unit of luminous intensity in the International System of Units (SI); that is, luminous power per unit solid angle emitted by a point light source in a particular direction. The units of luminous intensity based on flame or incandescent filament standards in use in various countries before 1948 were replaced initially […]


Light is part of the electromagnetic radiation within the portion of the electromagnetic spectrum which ranges from radio waves to gamma rays. Visible light is not inherently different from the other parts of the electromagnetic spectrum with the exception that the human eye can detect visible waves. Electromagnetic radiation can also be described in terms of a stream […]


Specific weight. Apparent weight.


An absorber is any material that is efficient at stopping (absorb) ionizing radiation from passing through. Absorbers can be made of a variety of materials, depending on the purpose; lead, tungsten and liquid hydrogen are common choices. Most absorbers are used as part of a particle detector, particle accelerators use absorbers to reduce the radiation damage on […]


In general, work is defined as a productive activity, which implies the implementation of rigorous and methodical, intellectual and/or manual knowledge, to produce and distribute goods and services in exchange for compensation, monetary or otherwise, an important topic of study for both social sciences (sociology, politics, law, economics) that the abstract and natural sciences (physics and geography). […]

Surface tension

The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. In the International System, it is measured in Pascal. The molecules at the surface do not have other like molecules on all sides of them […]


Adhesion is the set of physicochemical phenomena that occur in the molecular attraction between two materials of different nature placed in contact. Thus the force depends on the nature of the materials, temperature, and the pressure between the surfaces. Adhesion is due to intermolecular forces of the same kind as that causing cohesion. While the term […]

Electric field

The electric field is defined as the electric force per unit charge; it surrounds an electric charge, and exerts a force on other charges in the field, attracting or repelling them. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is […]

Electric charge

The electric charge is a type of physical property of matter, scalar and signed, responsible for one of the fundamental interactions of matter, the electromagnetic interaction, and the source of the electromagnetic field. There are two types of electric charges: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike […]


The average speed of an object is defined as the distance traveled divided by the time elapsed. The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is a vector quantity, and average velocity can be defined as […]


The speed, according to its technical definition in kinematics, is a scalar quantity that indicates the rate of motion distance per time and represents the magnitude of the change in position of an object. Its units are length and time. \[v=\dfrac{d}{t}\] where \(v\) is speed (also called average speed), \(d\) is distance, and \(t\) is time. […]

Magnetic field

A magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials.

Renewable and Non-Renewable resource

Renewable resources Renewable resources, whether they are material or energy, are natural resources which, due to natural characteristics or due to the production of man, are renewed over time (at a higher, or equal, renewal rate than the rate of consumption/use) and can be considered inexhaustible, or may be available for use by humans almost […]

Brownian motion

The brownian motion is the mathematical model used to describe the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid.


Vaporization. Evaporation. Water vapor. Saturated vapor. Wet saturated vapor. Dry saturated vapor. Superheated vapor.


Reflection is the change in direction (rebounding) of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Most objects are visible because of the light that reflects from them.


In physics, refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium with a different refractive index (\(n\)). In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material. This […]


Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. In general, diffraction is defined as the spreading or bending of waves as they pass round the edge of an obstacle or through an opening whose size is roughly the same as the wavelength of the waves. The disturbed […]


Astronomy is defined as the study of the objects that lie beyond our planet Earth and the processes by which these objects interact with one another. But it is much more. It is also humanity’s attempt to organize what we learn into a clear history of the universe, from the instant of its birth in the […]

Static electricity

Static electricity is the superficial and localized accumulation of electric charges on a body. It can occur both in a conductive material and in an insulator. It was discovered centuries ago that certain types of materials would mysteriously attract one another being rubbed together. For example: after rubbing a piece of silk against a piece […]

Electrostatic induction

Electrostatic induction is a redistribution of electric charge in an object, caused by the influence of nearby charges, and a method to create or generate static electricity in a material by bringing an electrically charged object near it. This causes the electrical charges to be redistributed in the material, resulting in one side having an […]

Particle beam

A particle beam is an ensemble of charged or neutral particles that move together in close proximity, in many cases moving at near the speed of light. A beam is characterized by a few basic parameters such as the particle species and the average energy of the particles. The beam of particles must be well collimated so […]


Seismic magnitude scales. Seismometer.


Classical physics. Modern physics. Biophysics.

Lenz’s law

Lenz’s law, named after the physicist Emil Lenz (pronounced /ˈlɛnts/) who formulated it in 1834, states that the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.

Coulomb’s law

Coulomb’s law, or Coulomb’s inverse-square law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles; or the force exerted by an electric field on an electric charge. This is the force that acts between electrically charged objects and is operationally defined by the value of the interaction […]

Biot–Savart law

The Biot–Savart law is an equation describing the magnetic field generated by a constant electric current. It relates the magnetic field to the magnitude, direction, length, and proximity of the electric current.

Abbe number

In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is an approximate measure of the material’s dispersion (change of refractive index versus wavelength), with high values of V indicating low dispersion. It is named after Ernst Abbe (1840-1905), the German physicist who defined it. The term V-number should not be […]

Ohm’s law

Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship: \[I=\dfrac{V}{R}\] where \(I\) is the current through the conductor in units of amperes, \(V\) is the […]

Electromagnetic field

An electromagnetic field (also EM field) is a classical field produced by moving electric charges. Consisting of the combination of the electric field and the magnetic field, it is generated locally by any distribution of electric charge that varies over time and propagates in space in the form of electromagnetic waves. The electromagnetic field interacts in space […]


The atmosphere is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is more likely to be retained if the gravity it is subject to is high and the temperature of the atmosphere is low.


A thermodynamic system or process is called adiabatic when occurs without the transfer of heat or mass of substances between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as work. The adiabatic process provides a rigorous conceptual basis for the theory used to expound the first law of […]

Sublimation (phase transition)

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state; this transformation occurs with heat acquisition and is, therefore, an endothermic process. Usually, in normal environmental conditions, to pass from solid to gaseous state it is necessary to go through the liquid state. Under certain pressure conditions, as the […]


Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere.

Freezing (solidification)

Freezing (or solidification) is a phase transition where a liquid (a disordered structure) turns into a solid (a more ordered structure) when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to […]


Condensation is the change of the physical state of matter from the gas phase into the liquid phase, transferring heat to the external environment (the inverse process of vaporization). It is a phase transition not characterized by a specific value of temperature for each substance, nor of pressure; can be performed: at constant temperature by compression, […]

Deposition (phase transition)

Deposition is the phase transition in which gas transforms into solid without passing through the liquid phase. Deposition is a thermodynamic process. The reverse of deposition is sublimation and hence sometimes deposition is called desublimation.