Glossary Of Physics

This glossary of physics is a meticulously curated compendium of terms and concepts fundamental to physics, its intricate sub-disciplines, and the interconnected fields that orbit it. We're talking about the bedrock of mechanics, the intricate dance of materials science, the potent forces within nuclear physics, the elusive realm of particle physics, and the fundamental laws governing heat and energy in thermodynamics. Should your curiosity extend beyond these confines, a broader spectrum of scientific terminology can be found in related glossaries, such as the Glossary of chemistry terms, the Glossary of astronomy, the comprehensive Glossary of areas of mathematics, and the pragmatic Glossary of engineering. It's a rather extensive undertaking, I'll grant you, but someone has to catalogue the sheer chaos of existence.

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E
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See also
References
External links

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A

ab initio This refers to a mathematical model that attempts to describe atomic nuclei by directly solving the non-relativistic Schrödinger equation for all the nucleons and the forces that bind them. It’s a rather earnest effort, yielding precise results for the lightest nuclei, but naturally, it becomes more of an approximation as the nuclei get heavier. The universe, it seems, rarely cooperates perfectly.

Abbe number Also known as the V-number or constringence, this is a measure, particularly relevant in optics and lens design, of how much a transparent material disperses light. Specifically, it quantifies the variation of the refractive index with respect to the wavelength of light. Higher Abbe numbers signify less dispersion, meaning the material bends different colors of light less.

absolute electrode potential In the field of electrochemistry, this is the potential of an electrode measured relative to a universally accepted reference system, bypassing any additional metal-solution interfaces. It's an attempt at a true baseline, though "universal" is a rather ambitious claim in physics.

absolute humidity This is simply the ratio of the mass of water vapor present in a given sample of air to the total volume of that air sample. It’s a direct measure of moisture content, unburdened by temperature or pressure variations that complicate other humidity measures.

absolute motion A concept that posits motion relative to an absolute, unchanging frame of reference. Spoiler alert: such a frame is rather difficult to pin down.

absolute pressure This pressure is measured relative to a perfect vacuum, meaning its zero point is the absence of all pressure. Consequently, it's the sum of the gauge pressure (the pressure measured relative to atmospheric pressure) and the atmospheric pressure itself.

absolute scale Any system of measurement that commences at a natural minimum, or zero point, and progresses in a single direction. Unlike arbitrary scales, which can be set anywhere, an absolute scale’s zero is a fundamental limit, like the absence of temperature or motion.

absolute zero The theoretical nadir of temperature, the point at which all thermal motion ceases. Officially, it's defined as 0 Kelvin or −273.15 degrees Celsius (−459.67 degrees Fahrenheit). At this point, the enthalpy and entropy of an ideal gas would theoretically reach their absolute minimums, and the constituent particles would achieve their lowest possible vibrational state. A theoretical limit, of course, which we can approach but never quite touch.

absorption spectroscopy A collection of spectroscopic techniques that quantify how much electromagnetic radiation is absorbed by a sample. When a sample absorbs energy, specifically in the form of photons, its absorption varies with frequency or wavelength, creating what is known as an absorption spectrum. This method is applicable across the entire electromagnetic spectrum.

absorptivity This term, often used interchangeably with absorptivity, refers to the measure of the amount of light absorbed by a substance.

accelerating expansion of the universe This is the observation that the expansion of the universe is not only ongoing but is, in fact, speeding up. The farther away a galaxy is, the faster it recedes from us, and this recession velocity is continuously increasing over time. It’s a disconcerting thought, suggesting a future that stretches out, ever faster and farther.[1] [2] [3] [4]

acceleration The rate at which the velocity of an object changes over time. More precisely, it's the rate of change of the rate of change of an object's position. It’s the universe’s way of saying, “You’re not staying still, are you?”

acceleration due to gravity The acceleration imparted to an object solely by the force of gravitation. It's the universe's constant, gentle (or not so gentle) nudge.

accelerometer An instrument designed to measure the proper acceleration of a body, independent of any other forces acting upon it. It’s a device that feels the real acceleration, not just the effects of external forces.

acoustics The branch of physics dedicated to the study of sound: how it's produced, how it travels, and what effects it has. It’s the science of vibrations and echoes.

adhesion This is the force that causes dissimilar objects or surfaces to stick together. Think of tape clinging to a wall or glue bonding two pieces of wood. It's the opposite of cohesion, which is about like things sticking together.

adiabatic cooling The process by which the temperature of a substance decreases due to a decrease in pressure, without any heat being exchanged with the surroundings. Imagine expanding a gas – it cools down.

adiabatic heating Conversely, this is the increase in temperature of a substance due to an increase in pressure, again, without heat exchange with the environment. Compressing a gas makes it hotter.

adiabatic process A thermodynamic process that occurs without any transfer of heat or mass between a system and its surroundings. In such a process, any energy exchange with the surroundings is strictly in the form of work. This concept is crucial for understanding the first law of thermodynamics, providing a rigorous foundation for its principles.[5] [6]

aerodynamics This is the fascinating study of how air, or any gas, moves, and more specifically, how it interacts with solid objects. Think of an airplane wing cutting through the air; aerodynamics is the physics behind that interaction. It’s a subset of fluid dynamics and gas dynamics, sharing many theoretical underpinnings.

aerophysics This term encompasses the study of air itself and the design, construction, and operational principles of devices that traverse the atmosphere at high speeds, such as aircraft, missiles, and rockets. It bridges the gap between pure physics and practical engineering.

afocal system An optical system that does not converge or diverge light beams; it has an infinite effective focal length.[7] This is often achieved by pairing two optical elements where the distance between them equals the sum of their individual focal lengths. It’s like a telescope that doesn't magnify, but rather changes the beam's collimation.

air mass

In meteorology, this refers to a large body of air characterized by its uniform temperature and water vapor content. These masses can span vast regions and tend to adopt the properties of the surface beneath them, often classified by latitude and source region.
In astronomy, it signifies the "amount of air one is looking through"[8] when observing celestial objects from within Earth's atmosphere. It's essentially an integral of air density along the light path, affecting how we perceive the light.

air mass coefficient This coefficient quantifies the direct optical path length of solar radiation through the Earth's atmosphere, expressed as a ratio relative to the vertical path at the zenith. It's used to understand how atmospheric travel modifies the solar spectrum.

albedo The fraction of total incident light that a surface, particularly a celestial body, reflects back in all directions. It's a measure of reflectivity.

alloy A metallic substance formed by mixing a metal with one or more other metals or non-metallic elements. It's metallurgy's way of creating materials with enhanced properties.

alpha decay Also known as α-decay, this is a type of radioactive decay where an atomic nucleus emits an alpha particle, transforming into a different nucleus. The mass number decreases by four, and the atomic number decreases by two. It's a fundamental process in nuclear physics.

alpha particle (α) Also symbolized as α 2+ , He 2+ , or 4 2 He 2+ , this is a subatomic particle consisting of two protons and two neutrons bound together, essentially the nucleus of a helium-4 atom. It carries a +2 elementary charge and a mass of approximately 4 atomic mass units. Alpha particles are typically emitted during radioactive alpha decay.

alternating current (AC) This is a form of electric current where the flow of electric charge periodically reverses direction. It's the current that powers most of our homes and devices, a constant push and pull. Contrast this with direct current (DC).

ammeter An instrument specifically designed to measure electric current. A straightforward tool for a fundamental electrical quantity.

amorphous solid A type of solid that lacks a definite, ordered geometric structure. Think of glass or certain plastics; they have rigidity but no long-range crystalline order.

ampere (A) Often shortened to "amp," this is the SI base unit for electric current. It's defined as the flow of one coulomb of electric charge per second. It quantifies the rate of electrical flow.

amplifier Also informally called an "amp," this is an electronic device capable of increasing the power of a signal, typically a time-varying voltage or current. It takes a weak input signal and produces a stronger output signal, using power from a power supply. The amount of amplification is measured by its gain. By definition, an amplifier must have a power gain greater than one.[9] [10] [11]

amplitude The maximum displacement or extent of oscillation, measured from the equilibrium or resting position. It’s the height of a wave, essentially.

angle of incidence In geometric optics, this is the angle formed between an incident ray striking a surface and the normal, a line perpendicular to the surface at the point of incidence. This applies to any wave – light, sound, microwaves, even X-rays.

angle of reflection This describes the change in direction of a wavefront when it encounters an interface between two different media, causing it to return into the medium from which it originated. The law of reflection states that for specular reflection, the angle of incidence equals the angle of reflection. It’s why mirrors work.

ångström (Å) A unit of length, equal to 10⁻¹⁰ meters, primarily used for measuring atomic and subatomic distances. It's a scale for the incredibly small.

angular acceleration The rate at which an object's angular velocity changes over time. In three dimensions, it's a pseudovector. Its SI unit is radians per second squared (rad/s²), typically denoted by the Greek letter alpha (α). There are two types: spin and orbital, reflecting the change in spin or orbital angular velocity, respectively. Interestingly, it doesn't always require an external torque; a figure skater speeding up her spin by pulling in her arms is a prime example.[12]

angular displacement The angle, measured in radians, degrees, or revolutions, through which a point or object has rotated around a specific axis. It's the measure of rotational change.

angular frequency (ω) Also known as angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, or pulsatance, this is a scalar measure of how fast something rotates or oscillates. It quantifies the rate of change of phase in a sinusoidal waveform or the angular displacement per unit time. It's related to the ordinary frequency (f) by the equation ω = 2πf, where f is in hertz and ω is in radians per second.[13] [14]

angular momentum Often referred to as the rotational equivalent of linear momentum. It's a crucial conserved quantity in physics, meaning the total angular momentum of a closed system remains constant. It's essentially the "oomph" of rotation.

angular velocity (ω) This measures how fast an object rotates or revolves relative to another point. It describes the rate of change of angular position over time. It can be spin angular velocity (rotation about its own center) or orbital angular velocity (revolution around an external point). The SI unit is radians per second (rad/sec). Conventionally, counter-clockwise rotation is positive, and clockwise is negative. The Greek letter omega (ω) is the usual symbol.[13]

anion An ion carrying a net negative electric charge. The opposite of a cation.

annihilation In particle physics, this is the process where a subatomic particle collides with its corresponding antiparticle, resulting in their mutual destruction and the creation of other particles, often photons.[15] The total energy and momentum are conserved, and since antiparticles have opposite quantum numbers to particles, the resulting particles have a net quantum number of zero.[16]

anode The electrode where conventional electric current enters a polarized electrical device. Electrons, conversely, flow out of the anode. In a galvanic cell, it's the negative terminal; in an electrolytic cell, it's the positive one. It's where oxidation occurs. Contrast with cathode.

anti-gravity A theoretical concept proposing a way to create a region or object that is unaffected by the force of gravity. It's distinct from simply being in free fall or orbit, or counteracting gravity with other forces.

antimatter Matter composed of antiparticles, mirroring ordinary matter but with opposite charges and quantum numbers. When matter and antimatter meet, they annihilate each other in a burst of energy.

antineutron The antiparticle of the neutron. It has the same mass and no net electric charge, but possesses an opposite baryon number and is composed of antiquarks.

antiparticle For every fundamental particle, there exists an antiparticle with the same mass but opposite electric charge and other quantum numbers. For example, the antiparticle of the electron is the positron. Some particles, like the photon, are their own antiparticles.

antiproton The antiparticle of the proton, possessing the same mass but a negative electric charge and an opposing magnetic moment.[17]

antiquark The antimatter counterpart to a quark. Antiquarks have the same mass but opposite electric charge and other quantum numbers.

arc length The distance along a curved line or arc.

Archimedes' principle This fundamental principle of fluid mechanics states that the upward buoyant force exerted on an object immersed in a fluid is equal to the weight of the fluid displaced by the object. This force acts at the center of mass of the displaced fluid.[18]

area moment of inertia A geometric property of a cross-section used in structural engineering to calculate the resistance of a beam to bending.

astrophysics A branch of astronomy that applies the principles of physics to understand the Universe, focusing on the physical nature and behavior of celestial objects rather than just their positions or motions.

attenuation coefficient A measure of how much the intensity of an energy beam, such as ultrasound or X-rays, is reduced as it passes through a material.[19]

atom The fundamental building block of matter, consisting of a central nucleus (containing protons and neutrons) surrounded by a cloud of electrons.

atomic line filter A filter that transmits only a specific wavelength of light emitted or absorbed by a particular atom.

atomic mass The mass of an atom, typically expressed in unified atomic mass units.

atomic mass unit A unit of mass used to express atomic and molecular masses. Historically, it was based on oxygen, but is now defined as one-twelfth the mass of a carbon-12 atom.

atomic number (Z) The number of protons in the nucleus of an atom, which uniquely identifies a chemical element. It's the primary organizing principle of the periodic table.

atomic orbital A mathematical function describing the wave-like behavior of an electron in an atom. It defines the region of space where an electron is likely to be found.

atomic packing factor A measure of the efficiency with which atoms are packed in a crystalline solid structure.

atomic physics The branch of physics that studies atoms as isolated systems, focusing on their electronic structure and interactions. It's distinct from nuclear physics, which deals with the nucleus itself.

atomic structure The arrangement of electrons, protons, and neutrons within an atom.

atomic weight (A) Historically, the average mass of atoms of an element, calculated using the relative abundance of isotopes. More precisely, it refers to the mass number for a specific isotope.

audio frequency Also known as audible frequency (AF), this refers to vibrations within the range of human hearing, typically from 20 Hz to 20,000 Hz. It's what we perceive as sound pitch.

Avogadro constant The number of constituent particles (such as atoms or molecules) per mole of a substance. Its exact value is 6.02214076×10²³ mol⁻¹.

Avogadro number This is simply the numerical value of the Avogadro constant, representing the number of entities in one mole of a substance.

Avogadro's law A gas law stating that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. It implies that the volume of a gas is directly proportional to the number of moles.

axion A hypothetical elementary particle proposed to explain the rarity of certain charge-parity symmetry-violating processes. It is theorized to be very light, electrically neutral, and pseudoscalar.

azimuthal quantum number Also known as the orbital quantum number, this quantum number describes the shape of an atomic orbital and determines its orbital angular momentum.

B

Babinet's principle A theorem in diffraction theory stating that the diffraction pattern produced by an opaque object is identical to that produced by a hole of the same size and shape, except for the overall intensity of the forward beam. It's a rather elegant symmetry in wave behavior.

background radiation The ubiquitous ionizing radiation that permeates the environment and to which the general population is exposed. It's the universe's ambient hum.

balanced forces When all the forces acting on an object cancel each other out, resulting in no net force. The object remains at rest or continues in uniform motion. It's equilibrium.

ballistics The science of the motion of projectiles, particularly bullets, rockets, and missiles. It’s the physics of flight, often with explosive beginnings.

Balmer series A set of spectral lines emitted by hydrogen atoms in the visible spectrum. Discovered by Johann Balmer, these lines are described by the Balmer formula and are a cornerstone of atomic spectroscopy.

barometer An instrument used to measure atmospheric pressure. Changes in pressure can often forecast short-term weather shifts.

baryon A class of composite subatomic particles, such as protons and neutrons, made up of three quarks. Most of the ordinary matter we encounter is baryonic. They are a type of fermion.

battery (electricity) A device that converts chemical energy into electrical energy, consisting of two or more connected electrical cells.

beam A structural element designed to resist loads primarily through bending. Found in buildings, bridges, and even machine frames, beams are fundamental to structural integrity.

bending Also known as flexure, this describes the behavior of a structural element, like a beam, when subjected to a load perpendicular to its longitudinal axis, causing it to deform.

bending moment The internal reaction within a structural element caused by an external force or moment, leading to bending. Beams are particularly susceptible to bending moments.[20] [21]

Bernoulli equation An equation describing the conservation of energy in fluid flow.

Bernoulli's principle In fluid dynamics, this principle states that an increase in the speed of a fluid is accompanied by a decrease in pressure or a decrease in the fluid's potential energy. It explains phenomena from airplane lift to why a shower curtain billows inward.[22] : Ch.3 [23] : 156–164, § 3.5

Bessel function A solution to Friedrich Bessel's differential equation, these functions are crucial in solving problems involving wave propagation and potential theory, particularly in cylindrical coordinates and spherical coordinates.[25]

beta decay Also denoted as β-decay, this is a type of radioactive decay in which an atomic nucleus emits a beta particle (an electron or positron), transforming into a different nuclide.

beta particle A high-energy, high-speed electron or positron emitted from the nucleus of a radioactive atom during beta decay.

Big Bang The prevailing cosmological model that describes the origin and early evolution of the Universe. It posits that the universe began in an extremely hot, dense state and has been expanding and cooling ever since.

binding energy The energy required to disassemble a system into its constituent parts. For bound systems, this energy is negative, indicating that the combined entity has lower energy than its separate components.

binomial random variable A random variable that describes the number of successes in a fixed number of independent Bernoulli trials.

biocatalysis The process of accelerating a chemical reaction using biological catalysts, such as enzymes.

biophysics An interdisciplinary field that applies the principles and methods of physics to the study of biological systems. It seeks to understand life at its most fundamental physical level.

black body An idealized object that absorbs all incident electromagnetic radiation without reflection. It's a theoretical construct used in thermodynamics to study radiation emission.

black-body radiation The electromagnetic radiation emitted by a black body in thermal equilibrium with its surroundings. Its spectrum is solely dependent on the temperature of the body, a fundamental concept in quantum physics.

block and tackle A system of pulleys and ropes used to lift or pull heavy loads by multiplying force. A classic example of mechanical advantage.

Bohr model An early model of the atom that proposed electrons orbit the nucleus in specific energy levels. While superseded, it was a crucial step in understanding atomic structure.

boiling point The temperature at which the vapor pressure of a liquid equals the ambient pressure, causing it to transition into a gas.

boiling point elevation The phenomenon where the boiling point of a liquid solvent increases when a non-volatile solute is dissolved in it. The resulting solution has a higher boiling point than the pure solvent.

Boltzmann constant A fundamental physical constant that relates the average kinetic energy of particles in a gas to the temperature of the gas. It's a bridge between the microscopic and macroscopic worlds.

Bose–Einstein condensate (BEC) A state of matter formed by cooling a gas of bosons to near absolute zero, where a large fraction of the bosons occupy the lowest quantum state, behaving like a single quantum entity.

boson A type of subatomic particle that follows Bose–Einstein statistics and has integer spin. Examples include photons, gluons, and the Higgs boson. Unlike fermions, multiple bosons can occupy the same quantum state.

Boyle's law A gas law stating that at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

Bra–ket notation A standard notation in quantum mechanics for representing quantum states and operators.

Bragg's law A law describing the diffraction of X-rays by crystals, relating the wavelength of the X-rays, the spacing between crystal planes, and the angle of diffraction.

bremsstrahlung Radiation produced when a charged particle is decelerated as it passes through matter. It's often seen in X-ray tubes.

Brewster's angle Also known as the polarization angle, this is the specific angle of incidence at which light with a particular polarization is completely transmitted through a transparent dielectric surface without reflection. Unpolarized light incident at this angle will be reflected in a perfectly polarized state.

british thermal unit (btu) An older unit of energy, defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Largely replaced by the joule in scientific contexts.

brittleness The tendency of a material to fracture with little or no plastic deformation when subjected to stress. Brittle materials absorb less energy before breaking.

Brownian motion The random movement of particles suspended in a fluid (liquid or gas) resulting from their continuous bombardment by the molecules of the fluid. It provides compelling evidence for the existence of atoms and molecules.

bubble A globule of gas enclosed within a liquid or solid.

Bulk modulus A measure of a substance's resistance to uniform compression. It is defined as the ratio of the applied pressure to the resulting fractional decrease in volume. Its SI unit is the pascal.

buoyancy The upward force exerted by a fluid that opposes the weight of an immersed object. It's why things float.

C

calculus A fundamental branch of mathematics dealing with change. It comprises differential calculus, which studies rates of change and slopes, and integral calculus, which deals with accumulation and areas. These two are linked by the fundamental theorem of calculus.

capacitance The ability of a system to store electric charge. It's defined as the ratio of the change in electric charge to the corresponding change in electric potential. The SI unit is the farad.

capacitive reactance The opposition offered by a capacitor to the flow of alternating current, which is inversely proportional to the frequency and capacitance.[24]

capacitor An electrical component consisting of two conductive plates separated by an insulating dielectric material, used to store electrical energy in an electric field.

Carnot cycle A theoretical thermodynamic cycle that sets the maximum possible efficiency for converting heat into work. It’s an idealization used to understand the limits of heat engines.

Cartesian coordinate system A coordinate system that defines each point in space by its signed distances from a set of mutually perpendicular axes. It's the familiar (x, y, z) system.

cathode The electrode through which conventional electric current flows out of a polarized electrical device. In a galvanic cell, it's the positive terminal; in an electrolytic cell, it's the negative one. It's where reduction occurs. Contrast with anode.

cathode ray A beam of electrons emitted from the negative electrode (cathode) in a vacuum tube.

cation An ion carrying a net positive electric charge. The opposite of an anion.

celestial mechanics The branch of astronomy and physics that deals with the motion of celestial bodies, governed by the laws of gravitation.

Celsius scale Also known as the centigrade scale, this is a widely used scale for measuring temperature. Water freezes at 0°C and boils at 100°C at standard atmospheric pressure.

center of curvature The center of the sphere or circle of which an arc or surface is a part.

center of gravity The point in a body where the force of gravity can be considered to act. For uniform gravitational fields, it coincides with the center of mass.

center of mass The unique point in space representing the average position of all the mass in a system. It's the point where an object would balance.

center of pressure The point on a submerged surface where the resultant hydrostatic force acts.

centigrade See Celsius scale.

central-force problem A classic problem in potential theory describing the motion of a particle under the influence of a force directed towards a fixed center. Gravity and electromagnetism are examples of central forces.

centrifugal force An apparent outward force experienced by an object moving in a curved path. It's a consequence of inertia, often described as a fictitious force in a rotating frame of reference.

centripetal force A real force directed towards the center of a circular path, necessary to keep an object moving in that path. Without it, the object would move in a straight line due to inertia.

cGh physics A hypothetical framework in theoretical physics aiming to unify relativity, gravitation, and quantum mechanics by considering the fundamental constants speed of light (c), the gravitational constant (G), and Planck constant (h) as dimensions. The realm where all three constants are simultaneously significant, quantum gravity, remains the most challenging corner.

chain reaction A self-sustaining series of reactions where a product of one reaction triggers subsequent similar reactions. Most notably seen in nuclear fission.

change of base rule A rule in logarithms that allows conversion between different bases.

charge carrier A mobile entity carrying an electric charge, such as an electron or ion, responsible for electric current.

chemical physics An interdisciplinary field that applies the principles of physics to study chemical phenomena and processes.

chromatic aberration An optical distortion where a lens fails to focus all colors of light to the same point, resulting in color fringing.

circular motion Motion along the path of a circle.

classical mechanics Also known as Newtonian mechanics, this is the branch of physics that describes the motion of macroscopic objects under the influence of forces, based on Newton's laws of motion.

coefficient of friction A dimensionless quantity representing the ratio of the force of friction between two bodies and the normal force pressing them together.

coherence A property of waves where their phase relationship is constant over time and space. Lasers produce highly coherent light.

cohesion The tendency of similar particles or surfaces to cling to one another. It's the force that holds molecules of the same substance together, contrasting with adhesion.

cold fusion A hypothesized type of nuclear reaction that would occur at or near room temperature, unlike conventional fusion which requires extremely high temperatures. It remains a controversial and unproven phenomenon.

complex harmonic motion The superposition of two or more simple harmonic motions, resulting in more intricate oscillatory patterns.

composite particle A particle made up of two or more smaller particles, such as protons and neutrons (which are made of quarks).

Compton scattering The scattering of a photon by a charged particle, typically an electron, resulting in a decrease in the photon's energy (and an increase in wavelength) and the acceleration of the electron. The opposite is inverse Compton scattering.

concave lens A lens that is thinner in the middle than at the edges, causing parallel light rays to diverge.

condensation point The temperature at which a gas or vapor turns into a liquid. It's the same as the boiling point at a given pressure.

condensed matter physics A major branch of physics that studies the macroscopic and microscopic physical properties of matter, particularly the solid and liquid phases.

conservation of momentum A fundamental principle stating that the total momentum of a closed system remains constant over time.

conservation law A principle stating that a particular quantity (e.g., energy, momentum) remains constant in an isolated physical system.

constructive interference The superposition of two or more waves that results in a wave of increased amplitude. This occurs when wave crests align with crests and troughs with troughs.

continuous spectrum A spectrum in which there are no gaps, containing radiation over a range of wavelengths. Stars emit continuous spectra.

continuum mechanics A branch of mechanics that treats matter as a continuous medium rather than as discrete atoms or molecules. It's used to study the behavior of fluids and solids.

convection The transfer of heat through the movement of fluids (liquids or gases). Hotter, less dense fluid rises, while cooler, denser fluid sinks, creating a circulation.

convex lens A lens that is thicker in the middle than at the edges, causing parallel light rays to converge.

coulomb (C) The SI derived unit of electric charge. It's defined as the charge transported by a constant current of one ampere in one second.

Coulomb's law The fundamental law describing the electrostatic force between two point charges, stating that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

converging lens See convex lens.

cosmic background radiation The faint electromagnetic radiation filling the universe, considered a remnant of the Big Bang.

creep The tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses. It's often observed at high temperatures.

crest The highest point of a wave cycle.

crest factor The ratio of the peak value of a waveform to its root mean square (RMS) value.

critical angle The angle of incidence above which a ray of light striking an interface between two media is totally internally reflected.

critical mass The minimum amount of fissile material required to sustain a nuclear chain reaction.

cube of theoretical physics See cGh physics.

Curie temperature The temperature above which a ferromagnetic material loses its permanent magnetism and becomes paramagnetic.

current density The electric current per unit area, flowing perpendicular to the current.

current length This seems to be a placeholder or a term not commonly used in standard physics. It might refer to the instantaneous length of a conductor carrying current, but without further context, its meaning is ambiguous.

curvilinear motion Motion along a curved path. Both planar and cylindrical coordinate systems are used to describe it.

cyclotron A type of particle accelerator that uses a magnetic field to accelerate charged particles outwards from the center along a spiral path.

D

Dalton's law Specifically, Dalton's law of partial pressures states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases.

damped vibration Oscillations that decrease in amplitude over time due to energy dissipation, often caused by friction or resistance.

Damping ratio A measure of how oscillations in a system decay after a disturbance. A high damping ratio means oscillations die out quickly.

Darcy–Weisbach equation An empirical equation used in fluid mechanics to calculate the pressure drop of a fluid in a pipe.

dark energy A mysterious form of energy hypothesized to permeate all of space and drive the accelerating expansion of the universe. Its nature remains one of the biggest puzzles in cosmology.

dark matter A hypothetical form of matter that does not interact with light or other electromagnetic radiation, making it invisible. Its existence is inferred from its gravitational effects on visible matter.

DC motor An electric motor that runs on direct current (DC) power.

decibel (dB) A logarithmic unit used to express the ratio of two values of a physical quantity, commonly used for sound intensity or signal power.

definite integral An integral that yields a numerical value, representing the net area under a curve between two specified limits.

deflection The displacement or bending of a structural element under load. It can be measured as an angle or a distance.

deformation The change in shape or size of a body due to applied forces or stresses.

density Also known as mass density, this is a fundamental physical property of a substance, defined as its mass per unit volume. It tells you how much "stuff" is packed into a given space.

derivative In calculus, the derivative measures the instantaneous rate of change of a function with respect to its variable. It's the slope of the tangent line at any point on a curve, fundamentally describing how things change.

destructive interference The superposition of two or more waves that results in a wave of reduced amplitude, often canceling each other out. This happens when wave crests align with troughs.

diamagnetism A property of materials that are weakly repelled by an external magnetic field. All materials exhibit diamagnetism to some extent.

dielectric An electrical insulator that can be polarized by an applied electric field. When placed in an electric field, charges within the dielectric shift slightly, creating an opposing internal field.

diffraction The phenomenon where waves bend and spread out as they pass through an opening or around an obstacle. It's a key characteristic of wave behavior.

direct current (DC) Electric current that flows in only one direction. Batteries provide DC power. Contrast with alternating current (AC).

dispersion The phenomenon where the speed of light in a medium depends on its wavelength, causing different colors to refract at slightly different angles. This is responsible for prisms splitting white light into a spectrum.

displacement A vector quantity representing the shortest distance from an object's initial position to its final position. It indicates both distance and direction, unlike scalar distance.

distance A numerical measure of how far apart two points or objects are. It's a scalar quantity.

drift velocity The average velocity attained by charged particles (like electrons in a conductor) in a material due to an electric field. It's typically much slower than the random thermal motion of the particles.

Doppler effect The change in frequency (and wavelength) of a wave in relation to an observer who is moving relative to the wave source. This is why the pitch of a siren changes as it passes.

drag A resistive force exerted by a fluid (liquid or gas) on an object moving through it, acting in the direction opposite to the object's motion. It depends on velocity, shape, and fluid properties.

ductility The ability of a solid material to deform under tensile stress without fracturing, often characterized by its ability to be drawn into a wire.

dynamics The branch of classical mechanics that studies forces and torques and their influence on motion, as opposed to kinematics, which describes motion itself.

dyne A unit of force in the cgs system, equal to the force required to accelerate a mass of one gram by one centimetre per second squared. It's an older unit, largely superseded by the newton.

E

econophysics An interdisciplinary field that applies the methods of physics to the study of economics.

elastic collision A collision in which both momentum and kinetic energy are conserved. Particles bounce off each other perfectly.

elastic energy Potential energy stored in a material when it is deformed elastically.

elastic instability A phenomenon where a structure loses its stability and undergoes large deformations under load, even if the stress remains below the material's yield strength.

elastic modulus A measure of a material's stiffness or resistance to elastic deformation. It relates stress to strain.

elasticity The property of a material that allows it to return to its original shape and size after being deformed.

electric charge A fundamental property of matter that causes it to experience a force when placed in an electric or magnetic field. It exists in positive and negative forms.

electric circuit A closed path through which electric current can flow, consisting of electrical components and a power source.

electric current The flow of electric charge through a conductor. Measured in amperes.

electric displacement field A vector field used in electromagnetism that relates to the electric field and the polarization of a dielectric medium.

electric field A region of space around an electric charge or a changing magnetic field where electric forces can be detected. It exerts a force on other charges.

electric field gradient The rate of change of the electric field with respect to position.

electric field intensity See electric field.

electric generator A device that converts mechanical energy into electrical energy, typically through electromagnetic induction.

electric motor A device that converts electrical energy into mechanical energy, using the interaction between magnetic fields and electric currents.

electric potential The amount of work needed per unit charge to move a charge from a reference point to a specific point in an electric field. Measured in volts.

electric power The rate at which electrical energy is transferred or consumed. Measured in watts.

electrical conductor A material that allows electric charge to flow freely through it, such as metals.

electrical insulator A material that strongly resists the flow of electric charge, such as rubber or glass.

electrical potential energy The potential energy a charged object possesses due to its position in an electric field.

electrical and electronics engineering An engineering discipline that deals with electricity, electronics, and electromagnetism.

electrical network A system of interconnected electrical components.

electrical resistance The opposition to the flow of electric current in a material or component. Measured in ohms.

electricity The phenomenon associated with the presence and flow of electric charge.

electro-optic effect Changes in the optical properties of a material in response to an applied electric field.

electrochemical cell A device that generates electric current from chemical reactions or uses electricity to drive chemical reactions.

electrodynamics The branch of physics that studies electric charges and currents and their interaction with electric and magnetic fields.

electrolytic cell An electrochemical cell that uses electrical energy to drive a non-spontaneous chemical reaction.

electromagnet A magnet whose magnetic field is produced by an electric current. The magnetism disappears when the current is turned off.

electromagnetic field A field that permeates space, consisting of electric and magnetic fields, generated by charged objects and varying currents. It mediates the electromagnetic force.

electromagnetic induction The production of an electromotive force (voltage) across an electrical conductor in a changing magnetic field. This is the principle behind electric generators.

electromagnetic radiation Energy that travels and spreads in the form of waves, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

electromagnetic spectrum The entire range of electromagnetic radiation, ordered by frequency or wavelength.

electromagnetic wave equation A set of equations that describe the propagation of electromagnetic waves.

electromagnetism The branch of physics that studies the phenomena associated with electric charges and currents, and their interactions with electric and magnetic fields.

electromechanics The study and application of the interplay between electrical and mechanical systems.

electromotive force (emf or E) The energy per unit charge supplied by a source of electrical energy, such as a battery or generator. It's the "electrical pressure" that drives current. Measured in volts.

electron A fundamental subatomic particle with a negative electric charge and a very small mass. Electrons orbit the atomic nucleus and are responsible for chemical bonding and electric current.

electron capture A type of radioactive decay in which an atomic nucleus absorbs an electron, converting a proton into a neutron and emitting a neutrino.

electron cloud The region around an atomic nucleus where electrons are likely to be found, described by atomic orbitals.

electron pair Two electrons, often with opposite spins, that are bound together.

electron paramagnetic resonance Also known as electron spin resonance (ESR), this is a spectroscopic technique used to study materials with unpaired electrons, exploiting the Zeeman effect.

electronvolt (eV) A unit of energy commonly used in particle physics, equal to the energy gained by an electron moving through an electric potential difference of one volt. Approximately 1.6×10⁻¹⁹ joules.

electronegativity A measure of the tendency of an atom or molecule to attract electrons or electron density towards itself in a chemical bond.

electronics The branch of physics and engineering that deals with the behavior and control of electrons, particularly in circuits containing active components like transistors and diodes.

electrostatics The study of stationary electric charges and the forces and fields they produce.

electrostriction The phenomenon where a dielectric material deforms in response to an applied electric field, regardless of the field's polarity.

elementary charge (e) The magnitude of the charge of a single proton or electron, approximately 1.602 × 10⁻¹⁹ coulombs.

elementary particle A particle that cannot be subdivided into smaller particles. Examples include quarks, leptons, and bosons.

emission spectrum A spectrum showing discrete lines of specific wavelengths emitted by excited atoms or molecules as they return to a lower energy state.

emissivity A measure of how effectively a surface emits thermal radiation, expressed as a fraction of the radiation emitted by a perfect black body at the same temperature.

energy The capacity to do work. It exists in various forms, such as kinetic, potential, thermal, and electromagnetic.

energy level Specific discrete values of energy that a quantum system, such as an atom or molecule, can possess.

endothermic Describes a process or reaction that absorbs energy from its surroundings, usually in the form of heat. Contrast with exothermic.

engineering physics An interdisciplinary field that combines principles of physics with engineering applications, often focusing on advanced technologies and materials.

enthalpy A thermodynamic property representing the total heat content of a system. It is the sum of the internal energy and the product of pressure and volume.

entropy A measure of the disorder or randomness in a system. According to the second law of thermodynamics, the entropy of an isolated system tends to increase over time.

equilibrant force A force that balances a system of other forces, bringing it into equilibrium.

equipartition In statistical mechanics, the principle that energy is distributed equally among all possible degrees of freedom of a system in thermal equilibrium.

escape velocity The minimum speed an object must achieve to overcome the gravitational pull of a celestial body and escape into space without further propulsion.

excited state A state of an atom, molecule, or nucleus in which its energy is higher than its ground state.

exothermic Describes a process or reaction that releases energy into its surroundings, usually in the form of heat. Contrast with endothermic.

experimental physics The branch of physics that relies on observation and experimentation to test theories and discover new phenomena.

F

farad (F) The SI derived unit of electrical capacitance. One farad is the capacitance of a capacitor across which a potential difference of one volt results in a stored charge of one coulomb.

falling bodies Objects moving under the influence of gravity, typically towards a larger celestial body.

faraday A unit of electric charge, equal to the charge of one mole of electrons.

Faraday constant The magnitude of the electric charge per mole of electrons, approximately 96,485 coulombs per mole.

Fermat's principle A principle in optics stating that light travels between two points along the path that requires the least time. This leads to the laws of reflection and refraction.

Fermi surface In solid-state physics, a surface in reciprocal space separating occupied electron states from unoccupied states at absolute zero temperature.

fermion A type of subatomic particle that obeys Fermi–Dirac statistics and the Pauli exclusion principle, meaning no two identical fermions can occupy the same quantum state. Examples include electrons, protons, and neutrons.

ferrimagnetism A type of magnetism similar to ferromagnetism, but where the magnetic moments of neighboring atoms are aligned in opposite directions with unequal magnitudes, resulting in a net magnetic moment.

ferromagnetism A property of materials, like iron, that exhibit a strong attraction to magnets and can be magnetized themselves. They possess spontaneous magnetic ordering below a certain temperature (the Curie temperature).

field line A graphical representation of a vector field, such as an electric or magnetic field. The lines indicate the direction and strength of the field.

first law of thermodynamics The principle of conservation of energy applied to thermodynamic systems. It states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

fission A nuclear reaction in which an atomic nucleus splits into two or more smaller nuclei, releasing a large amount of energy and neutrons.

flavour A property of quarks and leptons, analogous to electric charge, that distinguishes different types of these particles. There are six flavors of quarks (up, down, charm, strange, top, bottom) and six flavors of leptons (electron, muon, tau, and their corresponding neutrinos).

fluid A substance that can flow and take the shape of its container, exhibiting no resistance to shear stress. Liquids and gases are fluids.

fluid mechanics The branch of mechanics that studies the behavior of fluids (liquids, gases, and plasmas) at rest (fluid statics) and in motion (fluid dynamics).

fluid physics A broad term encompassing the study of the physical properties and behavior of fluids.

fluid statics The branch of fluid mechanics concerned with fluids at rest. It deals with concepts like pressure and buoyancy.

fluorescence A type of photoluminescence where a substance absorbs light at one wavelength and emits it at a longer wavelength almost instantaneously.

flux A measure of the flow of a substance or property through a surface. In physics, it often refers to the rate of flow of energy or particles.

flux density The amount of flux passing through a unit area. For magnetic fields, this is magnetic flux density, measured in teslas.

focal length The distance from the center of a lens or mirror to its focal point, where parallel rays of light converge or appear to diverge from.

focus The point at which parallel rays of light converge after passing through a lens or reflecting off a mirror.

force (F) An interaction that, when unopposed, will change the motion of an object. It has both magnitude and direction, making it a vector quantity. Measured in newtons.

force carrier A fundamental particle (like a photon or gluon) that mediates one of the fundamental forces of nature.

force field A region in space where a force can be detected, characterized by a vector at each point indicating the force's magnitude and direction.

frame of reference A coordinate system used to describe the position and motion of objects. The laws of physics are the same in all inertial frames of reference.

Fraunhofer lines Dark lines in the solar spectrum that correspond to specific wavelengths of light absorbed by elements in the Sun's atmosphere.

free body diagram A diagram used in physics to illustrate all the forces acting on an object.

frequency The number of cycles or oscillations of a wave or periodic phenomenon per unit time. Measured in hertz.

frequency modulation (FM) A method of encoding information in a carrier wave by varying its frequency.

free fall Motion under the sole influence of gravity. An object in free fall experiences weightlessness.

freezing point The temperature at which a substance transitions from a liquid to a solid state.

friction A force that opposes motion between surfaces in contact. It can be static (preventing motion) or kinetic (resisting motion).

function A relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output.

fundamental forces The four basic interactions in nature: strong nuclear, weak nuclear, electromagnetic, and gravitational. Also known as fundamental interactions.

fundamental frequency The lowest frequency of a periodic waveform, which determines the fundamental pitch of a sound.

fundamental theorem of calculus A theorem linking differential and integral calculus, stating that differentiation and integration are inverse operations.

fusion A nuclear reaction in which two or more atomic nuclei combine to form a heavier nucleus, releasing immense amounts of energy. This is the power source of stars.

G

gamma ray A high-energy form of electromagnetic radiation, typically produced by radioactive decay or nuclear reactions. They have very short wavelengths and high penetrating power.

gas One of the states of matter, characterized by having no fixed shape or volume, and consisting of particles that move randomly and rapidly.

general relativity Einstein's theory of gravitation, which describes gravity not as a force, but as a curvature of spacetime caused by mass and energy.

geophysics The branch of Earth science that applies the principles of physics to study the Earth and its atmosphere.

gluon The elementary particle that mediates the strong interaction, binding quarks together to form protons and neutrons.

Graham's law of diffusion States that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass.

gravitation Also known as gravity, this is the fundamental force of attraction between any two objects with mass. It governs the motion of planets, stars, and galaxies.

gravitational constant (G) A fundamental physical constant that appears in Newton's law of universal gravitation and Einstein's field equations. It determines the strength of the gravitational force.

gravitational energy The potential energy an object possesses due to its position in a gravitational field.

gravitational field A region of space around a massive body where gravitational forces can be detected. It's often visualized using field lines.

gravitational potential The work done per unit mass to move an object from a reference point to a specific point in a gravitational field.

gravitational wave Ripples in the fabric of spacetime, predicted by general relativity, caused by accelerating massive objects. Their detection confirmed a major prediction of Einstein's theory.

graviton A hypothetical elementary particle that mediates the force of gravitation. It is predicted to be massless and travel at the speed of light.

gravity See gravitation.

ground A common reference point in an electrical circuit, typically set to zero potential.

ground reaction force The force exerted by the ground on an object in contact with it, equal and opposite to the force exerted by the object on the ground (Newton's third law).

ground state The lowest possible energy state of a quantum mechanical system, such as an atom or molecule.

group velocity The velocity at which the envelope of a wave packet, representing the overall shape of the wave, propagates.

H

hadron A composite particle made of quarks and/or antiquarks, held together by the strong interaction. Protons and neutrons are examples of hadrons.

half-life The time required for half of a sample of a radioactive substance to undergo decay. It's a measure of radioactive decay rate.

Hamilton's principle A fundamental principle in classical mechanics stating that the path taken by a physical system between two points in time is the one that minimizes the action.

Hamiltonian mechanics A reformulation of classical mechanics that uses generalized coordinates and momenta, providing a more abstract and powerful framework.

harmonic mean A type of average, calculated as the reciprocal of the arithmetic mean of the reciprocals of the numbers.

heat Energy transferred between systems due to a temperature difference. It flows from hotter to colder objects.

heat transfer The study of the mechanisms by which thermal energy is exchanged between physical systems. The primary modes are conduction, convection, and radiation.

Helmholtz free energy A thermodynamic potential, defined as the internal energy minus the product of temperature and entropy. It represents the maximum amount of work that a thermodynamic system can perform at constant temperature and volume.

hertz (Hz) The SI unit of frequency, defined as one cycle per second.

Higgs boson An elementary particle in the Standard Model of particle physics that is associated with the Higgs field, which permeates space and gives mass to other fundamental particles.

homeokinetics The physics of complex, self-organizing systems.

horsepower (hp) A unit of power, historically used for engines. One horsepower is approximately 746 watts.

Huygens–Fresnel principle A principle that explains wave propagation by considering each point on a wavefront as a source of secondary spherical wavelets.

hydrostatics The branch of fluid mechanics that studies fluids at rest, including concepts like pressure and buoyancy.

I

ice point The temperature at which ice melts or water freezes at standard atmospheric pressure (0°C or 32°F).

impedance The total opposition that a circuit presents to alternating current, combining resistance and reactance. Measured in ohms.

implosion A process in which an object collapses or breaks inward due to external pressure being greater than internal pressure.

impulse The change in momentum of an object, equal to the product of the average force acting on it and the time interval over which it acts.

indefinite integral The antiderivative of a function, representing a family of functions differing by a constant.

inductance The property of an electrical conductor or circuit element to oppose a change in the electric current flowing through it, by storing energy in a magnetic field. Measured in henries.

infrasound Sound waves with frequencies below the lower limit of human audibility, typically below 20 Hz.

inertia The resistance of any physical object to any change in its state of motion; its tendency to remain at rest or in uniform motion in a straight line. It's quantified by mass.

inductive reactance The opposition offered by an inductor to the flow of alternating current, which is directly proportional to the frequency and inductance.

integral A fundamental concept in calculus representing the area under a curve or the accumulation of quantities.

integral transform A mathematical operation that converts a function from one domain to another, often simplifying analysis. Examples include the Laplace and Fourier transforms.

International System of Units (SI) The modern, standard system of measurement, based on seven base units (meter, kilogram, second, ampere, kelvin, mole, candela) and a decimal system of prefixes.

invariant mass In particle physics, a quantity that is the same for all observers, regardless of their frame of reference. It's related to the rest mass of a particle.

ion An atom or molecule that has gained or lost one or more electrons, resulting in a net electric charge.

ionic bond A chemical bond formed by the electrostatic attraction between oppositely charged ions.

ionization The process of converting an atom or molecule into an ion by adding or removing charged particles, typically electrons.

ionization chamber A type of radiation detector that measures ionizing radiation by detecting the ions produced when the radiation passes through a gas.

ionizing radiation Radiation with enough energy to remove electrons from atoms and molecules, such as alpha particles, beta particles, gamma rays, and X-rays.

isotope Atoms of the same element that have different numbers of neutrons in their nucleus. They have the same atomic number but different mass numbers.

J

Josephson effect A quantum mechanical phenomenon occurring in superconductors, where a supercurrent can flow across a thin insulating barrier between two superconductors.

joule (J) The SI derived unit of energy, work, or heat. It is defined as the work done when a force of one newton displaces an object by one meter.

jerk The rate of change of acceleration; the third derivative of displacement with respect to time. It describes how quickly acceleration changes.

K

Kelvin (K) The SI base unit of thermodynamic temperature. It is defined such that absolute zero is 0 K.

kinematics The branch of classical mechanics that describes motion without considering its causes. It focuses on displacement, velocity, and acceleration.

kinetic energy The energy possessed by an object due to its motion. It is given by the formula KE = ½mv², where m is mass and v is velocity. Contrast with potential energy.

Kirchhoff's circuit laws Two fundamental laws governing electric circuits: the current law (sum of currents entering a junction is zero) and the voltage law (sum of voltage drops around a closed loop is zero).

Kirchhoff's equations In fluid dynamics, these equations describe the motion of a rigid body within an ideal fluid.

L

Lagrangian mechanics A reformulation of classical mechanics that uses the Lagrangian function (kinetic energy minus potential energy) to describe the motion of a system.

laminar flow A flow regime characterized by smooth, parallel layers of fluid with no significant mixing between layers. Contrast with turbulent flow.

Laplace transform An integral transform used extensively in solving differential equations, particularly in engineering and physics.

Laplace–Runge–Lenz vector (LRL vector) A vector used in celestial mechanics that is conserved for systems with a 1/r² central force, describing the orientation of the orbit.

laser A device that emits a highly concentrated, monochromatic, and coherent beam of light through stimulated emission. The acronym stands for "light amplification by stimulated emission of radiation."

law of universal gravitation See Newton's law of universal gravitation.

LC circuit An electrical circuit consisting of an inductor (L) and a capacitor (C), used in resonant circuits and filters.

Lenz's law A law stating that the direction of an induced current in a conductor due to electromagnetic induction is such that it opposes the change in magnetic flux that produced it.

lepton A type of elementary particle that does not interact via the strong force. Electrons and neutrinos are examples of leptons.

lever A simple machine consisting of a rigid rod pivoted at a fixed point (fulcrum), used to multiply force or change its direction.

levitation The phenomenon of suspending an object in the air by means of magnetic or acoustic forces.

light Electromagnetic radiation within the range of wavelengths visible to the human eye. More broadly, it encompasses all electromagnetic radiation.

linear actuator A device that produces motion in a straight line.

linear algebra The branch of mathematics dealing with vector spaces, linear mappings, and systems of linear equations.

line of force A curve drawn in a force field such that its tangent at any point gives the direction of the force at that point.

linear elasticity A simplified model of material behavior where stress is directly proportional to strain, and the material returns to its original shape upon removal of the load.

Liouville's theorem A theorem in classical mechanics stating that the volume occupied by a system of particles in phase space is conserved over time.

liquid A state of matter with a definite volume but no fixed shape, taking the form of its container.

liquid crystal (LC) A state of matter with properties between those of a conventional liquid and a solid crystal, exhibiting ordered molecular arrangement.

longitudinal wave A wave in which the particles of the medium vibrate parallel to the direction of wave propagation, such as sound waves.

M

M-theory A proposed unified theory in string theory that encompasses five different superstring theories and 11-dimensional supergravity.

Mach number A dimensionless quantity representing the ratio of the speed of an object or fluid flow to the speed of sound in the surrounding medium.

Mach's principle A concept suggesting that an object's inertia is determined by its interaction with all the matter in the universe.

machine A device that uses mechanical power to perform some task. It typically involves multiple parts working together.

machine element A basic component of a machine, such as a gear, lever, or bearing.

Maclaurin series A specific case of the Taylor series, representing a function as an infinite sum of terms calculated from the function's derivatives at a single point (the origin).

magnetic field A vector field that describes the magnetic influence of electric currents and magnetic materials. It exerts forces on moving electric charges and magnetic dipoles.

magnetism A physical phenomenon produced by moving electric charges and electric currents, associated with magnetic fields.

magnetostatics The study of magnetic fields that are constant in time, typically produced by permanent magnets or steady electric currents.

mass A fundamental property of matter, representing its resistance to acceleration (inertia) and the strength of its gravitational attraction.

mass balance An accounting of all the mass entering, leaving, and accumulating within a system, based on the law of conservation of mass.

mass density See density.

mass flux The rate of mass flow per unit area.

mass moment of inertia The rotational analogue of mass, measuring an object's resistance to changes in its rotational motion.

mass number The total number of protons and neutrons (nucleons) in an atomic nucleus.

mass spectrometry An analytical technique used to measure the mass-to-charge ratio of ions, allowing for the identification and quantification of chemical substances.

material properties The characteristics of a material that describe its behavior under various physical conditions, such as strength, elasticity, and conductivity.

materials science An interdisciplinary field that studies the properties, structure, and applications of materials, often focusing on solids.

mathematical physics The application of advanced mathematical methods to problems in physics and the development of new mathematical techniques for physical theories.

mathematics The abstract study of quantity, structure, space, change, and related concepts.

matrix A rectangular array of numbers or symbols, used extensively in linear algebra and various areas of physics.

matter Anything that has mass and occupies space. It is composed of fundamental particles.

Maxwell's equations A set of fundamental equations that describe the behavior of electric and magnetic fields and their interactions with charges and currents. They form the basis of classical electrodynamics.

measure of central tendency A statistical value that represents the center or typical value of a dataset, such as the mean, median, or mode.

mechanical energy The sum of the kinetic and potential energy of an object.

mechanical filter A device that selectively transmits or blocks mechanical vibrations or waves.

mechanical equilibrium A state where the net force and net torque on an object are zero, resulting in no change in its state of motion.

mechanical wave A wave that requires a medium (solid, liquid, or gas) to propagate, such as sound waves.

mechanics The branch of physics that studies the motion of objects and the forces that affect motion.

melting Also known as fusion, this is the phase transition of a substance from a solid to a liquid state, occurring at its melting point.

meson A type of hadron composed of a quark and an antiquark. Mesons are typically unstable particles.

modulus of elasticity See elastic modulus.

molar concentration The amount of a substance in moles per unit volume of solution.

molar mass The mass of one mole of a substance, expressed in grams per mole (g/mol).

molecule A group of two or more atoms held together by chemical bonds.

molecular physics The branch of physics that studies the physical properties and behavior of molecules.

moment In physics, a measure of the tendency of a force or mass distribution to cause rotation about an axis.

moment of inertia The rotational analogue of mass, quantifying an object's resistance to angular acceleration.

momentum A vector quantity defined as the product of an object's mass and its velocity. It represents the "quantity of motion."

monochromatic light Light of a single wavelength or a very narrow range of wavelengths.

motion Any change in the position of an object over time. Described by concepts like velocity and acceleration.

muon An elementary particle, a type of lepton, similar to the electron but much more massive and unstable.

N

nanoengineering The application of engineering principles to the nanoscale, focusing on the design, fabrication, and use of nanoscale materials and devices.

nanotechnology The manipulation of matter on an atomic and molecular scale (typically 1 to 100 nanometers). It involves the design, production, and application of structures, devices, and systems through the control of matter on this scale.

Navier–Stokes equations A set of partial differential equations that describe the motion of viscous fluid substances. They are fundamental to fluid dynamics.

neurophysics An interdisciplinary field applying physics principles to understand the nervous system.

neutrino A very light, electrically neutral elementary particle that interacts only via the weak force and gravity. They are notoriously difficult to detect.

neutron A subatomic particle found in the nucleus of an atom, having no net electric charge and a mass slightly greater than that of a proton. It consists of one up quark and two down quarks.

prompt neutron Neutrons emitted immediately after a nuclear fission event.
delayed neutron Neutrons emitted from the radioactive decay of fission products, occurring seconds or minutes after fission.

neutron cross-section A measure of the probability that a neutron will interact with a nucleus.

newton (N) The SI unit of force, defined as the force required to accelerate a mass of one kilogram by one meter per second squared.

Newton's laws of motion Three fundamental laws that form the basis of classical mechanics:

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F=ma).
For every action, there is an equal and opposite reaction.

Newton's law of universal gravitation The law stating that every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

Newtonian fluid A fluid whose viscosity remains constant regardless of the shear rate or stress applied. Water and air are common examples.

Newtonian mechanics See classical mechanics.

normal force The component of a contact force that is perpendicular to the surface of contact. It prevents objects from passing through each other.

nuclear force The strong force that binds protons and neutrons together within the atomic nucleus.

nuclear physics The branch of physics that studies the atomic nucleus, its constituents (protons and neutrons), and the forces governing them.

nuclear reaction A process that involves changes in the nucleus of an atom, such as fission or fusion.

nuclear transmutation The conversion of one chemical element or isotope into another through nuclear reactions.

nucleon A constituent particle of the atomic nucleus, referring to either a proton or a neutron.

nucleus The dense, positively charged central core of an atom, containing protons and neutrons.

nuclide An atom characterized by a specific number of protons and neutrons in its nucleus.

O

ohm (Ω) The SI derived unit of electrical resistance. One ohm is the resistance between two points of a conductor when a constant potential difference of one volt, applied between these points, produces in this conductor a current of one ampere.

Ohm's law The relationship between voltage (V), current (I), and resistance (R) in an electrical circuit, stating that V = IR for a conductor at constant temperature.

optical tweezers Devices that use a highly focused laser beam to trap and manipulate microscopic dielectric objects.

optically detected magnetic resonance A technique combining optical spectroscopy with magnetic resonance to study the properties of materials.

optics The branch of physics that studies the behavior and properties of light, including its interaction with matter and the construction of optical instruments. It also applies to other forms of electromagnetic radiation.

P

paraffin A flammable, waxy solid mixture of hydrocarbons, often used as an insulator.

parallel circuit An electric circuit where components are connected across common points, so the voltage across each component is the same.

parity

(mathematics) A property of a function related to its symmetry.
(physics) A quantum mechanical property associated with the symmetry of a system's wave function under spatial inversion.

particle A small, discrete unit of matter or energy.

particle accelerator A device used to accelerate charged particles to very high speeds and energies, used in fundamental physics research and medical applications.

particle displacement The change in position of a particle.

particle physics The branch of physics that studies the fundamental constituents of matter and radiation, and the interactions between them.

Pascal's law A principle in fluid mechanics stating that pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

Pauli exclusion principle A fundamental principle in quantum mechanics stating that no two identical fermions (e.g., electrons) can occupy the same quantum state simultaneously.

pendulum A weight suspended from a pivot so that it can swing freely. Its motion is often used to illustrate principles of simple harmonic motion.

periodic table of the elements A tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties.

phase (matter) A distinct state of matter, such as solid, liquid, or gas, characterized by uniform physical properties.

phase (waves) The position of a point in time on a waveform cycle, often expressed as an angle.

phase equilibrium A state where different phases of a substance can coexist in equilibrium.

phenomenology The study of physical phenomena without necessarily delving into their underlying causes or fundamental principles.

phosphorescence A type of luminescence where a substance absorbs light and re-emits it slowly over time.

photoelectric effect The emission of electrons from a material when light shines on it. This phenomenon provided crucial evidence for the particle nature of light (photons).

photon The quantum of the electromagnetic field, including light. It is a massless particle that carries the electromagnetic force.

photonics The science and technology of light, encompassing its generation, detection, and manipulation.

physical chemistry The study of macroscopic, microscopic, and particulate phenomena in chemical systems by applying principles of physics.

physical constant A physical quantity that has a fixed numerical value, believed to be universal. Examples include the speed of light and Planck's constant.

physical quantity A property of a phenomenon, body, or substance that can be quantified by measurement.

physics The natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. It's the most fundamental of the natural sciences.

piezoelectricity The property of certain materials to generate an electric charge in response to applied mechanical stress, and vice versa.

pion A type of meson, composed of a quark and an antiquark, that plays a role in the strong interaction between nucleons.

Planck constant (h) A fundamental constant of nature that relates the energy of a photon to its frequency (E = hf). It is central to quantum mechanics.

Planck units A system of natural units of length, mass, time, etc., based on fundamental physical constants.

Planck's law A law describing the spectral distribution of black-body radiation as a function of temperature. It was a foundational step in the development of quantum theory.

plasma A state of matter consisting of ionized gas, where a significant fraction of the particles are charged. Often called the "fourth state of matter."

plasma physics The branch of physics that studies plasmas.

plasticity The ability of a solid material to undergo permanent deformation without fracturing when subjected to stress.

pneumatics The study and application of compressed gas to generate mechanical force and motion.

positron The antiparticle of the electron, having the same mass but a positive electric charge.

potential energy The energy stored in an object or system by virtue of its position or state. Examples include gravitational potential energy and elastic potential energy. Contrast with kinetic energy.

power The rate at which work is done or energy is transferred. Measured in watts.

pressure Force applied perpendicular to a surface per unit area.

principle of relativity The principle that the laws of physics are the same for all observers in uniform motion (inertial frames of reference).

probability A measure of the likelihood that an event will occur, expressed as a number between 0 and 1.

probability distribution A function that describes the likelihood of obtaining the possible values that a random variable can take.

probability theory The mathematical framework for quantifying uncertainty and randomness.

proton A subatomic particle found in the nucleus of an atom, carrying a positive electric charge and having a mass approximately equal to that of a neutron. It consists of two up quarks and one down quark.

psi particle A type of meson containing a charm quark and a charm antiquark.

pulley A simple machine consisting of a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt.

pulse A brief, transient disturbance or oscillation in a medium or field.

pulse wave A wave of increased pressure that propagates through a fluid or solid, often associated with biological systems like blood flow.

Q

quantization The process by which a physical quantity, such as energy or angular momentum, is restricted to discrete values. A core concept in quantum mechanics.

quantum The minimum discrete amount of any physical entity (such as energy or momentum) involved in an interaction.

quantum chromodynamics (QCD) The theory describing the strong interaction between quarks and gluons, which binds quarks together to form protons and neutrons.

quantum electrodynamics (QED) The quantum field theory of electromagnetism, describing the interaction between light and matter with extreme precision. It was the first theory to successfully reconcile quantum mechanics and special relativity.

quantum field theory A theoretical framework that combines quantum mechanics, special relativity, and classical field theory, used to describe elementary particles and their interactions.

quantum gravity A hypothetical theory that aims to unify quantum mechanics and general relativity to describe gravity at the quantum level.

quantum mechanics The fundamental theory in physics describing nature at the smallest scales of energy and matter, where classical physics breaks down. It deals with probabilities, wave-particle duality, and quantization.

quantum number A set of numbers that describe the state of a quantum system, such as an electron in an atom.

quantum physics See quantum mechanics.

quantum state A complete description of a quantum system, often represented by a wave function.

quark A fundamental constituent of matter, quarks combine to form hadrons like protons and neutrons. They are subject to the strong force and come in six "flavors."

quasiparticle An entity in condensed matter physics that behaves like a particle but is actually a collective excitation of the underlying system.

R

radiant energy Energy that is transmitted by electromagnetic radiation.

radiation The emission or transmission of energy in the form of waves or particles.

radioactive decay The spontaneous process by which an unstable atomic nucleus loses energy by emitting radiation, transforming into a different nucleus.

radionuclide An atom with an unstable nucleus that undergoes radioactive decay. Also known as a radioisotope or radioactive isotope.

radius of curvature The radius of the sphere or cylinder of which a lens or mirror surface is a part.

redshift The phenomenon where electromagnetic radiation from an object undergoes an increase in wavelength, typically observed for distant galaxies due to the expansion of the universe.

refraction The bending of a wave (like light or sound) as it passes from one medium to another, due to a change in speed.

refractive index A measure of how much light slows down when passing through a medium, related to the degree of refraction.

relative atomic mass The ratio of the average mass of atoms of an element to one-twelfth the mass of an atom of carbon-12.

relativistic mechanics The branch of mechanics that incorporates the principles of special relativity, dealing with objects moving at speeds close to the speed of light.

relativity Einstein's theories of special relativity and general relativity, which revolutionized our understanding of space, time, gravity, and the universe.

rest frame A frame of reference in which an object is considered to be at rest.

rigid body An idealized object whose shape and size do not change under the influence of external forces. In reality, all objects deform to some extent.

rotational energy The kinetic energy possessed by an object due to its rotation.

rotational speed The rate at which an object rotates, often measured in revolutions per minute (RPM) or radians per second.

Rydberg formula An empirical formula used to calculate the wavelengths of spectral lines emitted by hydrogen atoms.

S

scalar A quantity that is fully described by a single number, representing its magnitude. Examples include mass, temperature, and speed. Contrast with vector.

scattering The process by which particles or waves are deflected from their original trajectory due to interactions with other particles or obstacles.

science A systematic approach to acquiring knowledge about the natural world through observation, experimentation, and the formulation of testable explanations and predictions.

screw A simple machine that converts rotational motion into linear motion, providing mechanical advantage.

second law of thermodynamics A fundamental law stating that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases where the system is in a steady state or undergoing a reversible process. It implies a directionality to natural processes.

Seebeck effect The phenomenon where a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.

series circuit An electric circuit in which components are connected end-to-end, so the same current flows through each component.

shadow matter Hypothetical matter that interacts only through gravity, proposed as a candidate for dark matter.

shear modulus A measure of a solid material's resistance to shear deformation. Also known as the modulus of rigidity.

shear strength The maximum shear stress a material can withstand before failure.

shear stress Stress applied parallel to a surface, causing deformation.

shortwave radiation (SW) Electromagnetic radiation with wavelengths typically ranging from 0.1 to 5.0 micrometers, primarily from the sun.

Schrödinger equation The fundamental equation of quantum mechanics, describing how the quantum state of a physical system changes over time.

simple harmonic motion Oscillatory motion where the restoring force is directly proportional to the displacement from equilibrium. Examples include a mass on a spring and a simple pendulum.

simple machine A basic mechanical device that changes the direction or magnitude of a force. The six classical simple machines are the lever, wheel and axle, pulley, inclined plane, wedge, and screw.

siphon A tube used to transfer liquid from a higher reservoir to a lower one, utilizing atmospheric pressure and gravity.

Snell's law The law that describes the relationship between the angles of incidence and refraction and the refractive indices of the two media, governing how light bends when passing between them.

solar cell A device that converts sunlight directly into electricity using the photovoltaic effect.

solid A state of matter characterized by a definite shape and volume, with particles held in fixed positions.

solid mechanics The branch of mechanics that studies the behavior of solid materials under stress and strain.

solid-state physics The study of the physical properties of solid materials, particularly their electronic and magnetic properties.

solubility The ability of a solute to dissolve in a solvent to form a homogeneous solution. It depends on temperature, pressure, and the nature of the solute and solvent.

sonoluminescence The emission of light from collapsing bubbles in a liquid when excited by sound.

sound A mechanical wave that propagates through a medium (solid, liquid, or gas) as vibrations, typically within the range of human hearing.

special relativity Einstein's theory describing the relationship between space and time for objects moving at constant speeds, postulating that the laws of physics are the same for all non-accelerating observers and that the speed of light in a vacuum is constant.

specific activity The activity of a radioactive substance per unit mass.

speed The rate at which an object covers distance. It is the magnitude of velocity.

speed of light (c) The speed at which light propagates in a vacuum, a fundamental physical constant approximately equal to 299,792,458 meters per second. It is the ultimate speed limit in the universe.

speed of sound The speed at which sound waves propagate through a medium. It varies depending on the medium's properties (temperature, density, etc.).

spherical aberration An optical distortion where light rays passing through the edges of a spherical lens or mirror are focused at a different point than those passing through the center.

spin quantum number A quantum mechanical property of particles, representing their intrinsic angular momentum.

stable isotope ratio The relative abundance of naturally occurring, non-radioactive isotopes of a chemical element.

stable nuclide An atomic nuclide that does not undergo radioactive decay.

standard atomic weight The weighted average of the atomic masses of the naturally occurring isotopes of an element.

Standard Model The theory in particle physics that describes the known fundamental particles and three of the four fundamental forces (strong, weak, and electromagnetic), but not gravity.

standing wave A wave pattern formed by the superposition of two waves traveling in opposite directions, resulting in points of no motion (nodes) and maximum motion (antinodes).

state of matter The distinct forms in which matter can exist, such as solid, liquid, gas, and plasma.

statics The branch of mechanics concerned with forces acting on objects in equilibrium (not accelerating).

statistical mechanics A branch of physics that uses probability theory and statistics to study the behavior of large collections of particles, bridging the microscopic and macroscopic realms.

stiffness The resistance of an elastic body to deformation under an applied force. It's the inverse of compliance.

strain The measure of deformation representing the relative change in shape or size of a material under stress.

strain hardening The strengthening of a metal by plastic deformation.

strength of materials A field of mechanics that studies the behavior of solid materials under stress and strain, focusing on their load-bearing capacity.

stress

A measure of the internal forces within a deformable body, per unit area.
The applied force or system of forces tending to deform a physical body.

stress–strain curve A graphical representation of a material's response to applied stress, showing the relationship between stress and strain.

string duality In string theory, relationships suggesting that different string theories are actually different perspectives of a single underlying theory.

string theory A theoretical framework in physics that postulates that the fundamental constituents of the universe are one-dimensional vibrating strings, rather than point-like particles.

strong interaction One of the four fundamental forces, responsible for binding quarks together to form protons and neutrons, and holding atomic nuclei together. Also known as the strong force or strong nuclear force.

structural load Forces applied to a structure, such as weight, wind pressure, or seismic activity.

subatomic particle A particle smaller than an atom, such as a proton, neutron, or electron.

sublimation The direct transition of a substance from the solid to the gas phase without passing through the liquid phase. Dry ice (solid CO₂) sublimes at room temperature.

superconductivity A phenomenon observed in certain materials below a critical temperature, characterized by zero electrical resistance and the expulsion of magnetic fields.

superconductor A material exhibiting superconductivity.

superhard material Materials with a very high resistance to scratching and indentation, such as diamond and cubic boron nitride.

superposition principle In wave phenomena, the principle that the net displacement of the medium at any point where two or more waves overlap is the algebraic sum of the displacements due to each individual wave.

supersymmetry (SUSY) A proposed theoretical symmetry that relates two fundamental classes of particles: bosons and fermions. It predicts that every known particle has a "superpartner" with different spin.

surface tension The tendency of liquid surfaces to shrink into the minimum surface area possible. It arises from the cohesive nature of liquid molecules.

T

temperature A measure of the average kinetic energy of the particles in a substance, quantifying its hotness or coldness.

tensile modulus See Young's modulus.

tensile strength The maximum stress a material can withstand while being stretched or pulled before breaking.

tesla (T) The SI unit of magnetic flux density.

test particle In physics, a hypothetical particle with negligible mass and charge used to probe a field without significantly disturbing it.

theoretical physics The branch of physics that uses mathematical models and abstractions to explain and predict physical phenomena, complementing experimental physics.

theory of everything (ToE) A hypothetical framework in theoretical physics that fully explains and links together all known physical phenomena, unifying all fundamental forces and particles.

theory of relativity See relativity.

thermal conduction The transfer of heat through a material by direct contact of particles, without bulk movement of the material itself. Metals are good thermal conductors.

thermal equilibrium A state where there is no net flow of heat between systems in contact, meaning they are at the same temperature.

thermal radiation Electromagnetic radiation emitted by all matter above absolute zero temperature, due to the thermal motion of its atoms and molecules.

thermionic emission The release of electrons from a heated surface.

thermodynamic equilibrium A state of a system where its macroscopic properties (like temperature, pressure, and volume) are constant over time and there is no net flow of energy or matter.

thermodynamic free energy A thermodynamic potential that measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure (Gibbs free energy) or temperature and volume (Helmholtz free energy).

thermodynamics The branch of physics that deals with heat, work, temperature, and energy, and their interrelations. It governs the flow of energy in the universe.

thermometer An instrument used to measure temperature.

third law of thermodynamics A law stating that the entropy of a system approaches a constant minimum value as the temperature approaches absolute zero. It implies that absolute zero is unattainable.

threshold frequency The minimum frequency of light required to eject an electron from a metal surface in the photoelectric effect.

torque Also known as moment or moment of force, this is the rotational equivalent of force. It's the tendency of a force to rotate an object about an axis or pivot.

total internal reflection The phenomenon where a wave striking the boundary between two media is completely reflected back into the first medium when the angle of incidence exceeds the critical angle.

toughness The ability of a material to absorb energy and deform plastically before fracturing. It's a measure of resistance to fracture.

trajectory The path followed by a projectile or other moving object under the action of given forces.

transducer A device that converts one form of energy into another, such as a microphone (sound to electrical) or a loudspeaker (electrical to sound).

transmission medium The substance or material through which a wave propagates.

transverse wave A wave in which the particles of the medium move perpendicular to the direction of wave propagation, such as light waves or waves on a string.

trigonometry The branch of mathematics that studies triangles and the relationships between their sides and angles.

trimean A statistical measure combining the median, lower quartile, and upper quartile of a dataset.

triple point The specific temperature and pressure at which the solid, liquid, and gaseous phases of a substance coexist in thermodynamic equilibrium.

truncated mean A statistical measure calculated by discarding a fixed percentage of the lowest and highest values in a dataset before computing the mean.

U

unbalanced forces When the net force acting on an object is not zero. This results in acceleration, meaning the object's velocity changes.

uncertainty principle A fundamental principle of quantum mechanics stating that there is a limit to the precision with which certain pairs of physical properties of a particle, such as position and momentum, can be known simultaneously. The more precisely one is known, the less precisely the other can be known.

unified atomic mass unit Defined as 1/12th the mass of a neutral carbon-12 atom in its ground state. It is often referred to as a dalton.

uniform motion Motion at a constant velocity (constant speed and direction).

uniform circular motion Motion in a circle at a constant speed. Although the speed is constant, the velocity is continuously changing due to the changing direction, requiring a centripetal force.

unit vector A vector having magnitude 1, used to indicate direction.

utility frequency The frequency of alternating current (AC) used in power distribution systems, typically 50 or 60 Hz.

V

vacuum A space devoid of matter. In practice, a near-vacuum is a region where the pressure is significantly lower than atmospheric pressure.

valence electron An electron in the outermost shell of an atom that can participate in chemical bonding.

valence shell The outermost electron shell of an atom, containing the valence electrons.

valley of stability In nuclear physics, a region on a chart of nuclides representing the range of neutron and proton numbers for which nuclei are stable against radioactive decay.

Van de Graaff generator An electrostatic generator that produces very high voltages, used for particle acceleration and other high-voltage experiments.

variable capacitor A capacitor whose capacitance can be adjusted, often used in tuning circuits.

variable resistor A resistor whose resistance can be adjusted, also known as a potentiometer or rheostat.

vector A quantity that has both magnitude and direction. Examples include velocity, force, and displacement.

vector space A fundamental mathematical structure consisting of a set of vectors and operations of vector addition and scalar multiplication.

velocity (v) A vector quantity describing the rate of change of an object's position with respect to time. It specifies both speed and direction.

virtual image An image formed by the apparent divergence of rays, which cannot be projected onto a screen.

virtual particle A transient fluctuation of a quantum field that mediates forces between particles, existing for a very short time according to the uncertainty principle.

viscoelasticity The property of materials exhibiting both viscous (fluid-like) and elastic (solid-like) characteristics when undergoing deformation.

viscosity A measure of a fluid's resistance to flow. Thicker fluids have higher viscosity.

visible light The portion of the electromagnetic spectrum that is visible to the human eye, typically ranging from 400 to 700 nanometers in wavelength.

volt (V) The SI derived unit of electric potential difference or electromotive force. It is defined as the potential difference between two points when one joule of work is done to move one coulomb of charge between them.

Volta potential The difference in electric potential between two conductors or phases, specifically related to the work required to move a charge across their interface.

voltage See electric potential.

voltmeter An instrument used to measure the electric potential difference (voltage) between two points in an electric circuit.

volt per metre The SI unit of electric field strength, representing the electric force per unit charge.

volume The amount of three-dimensional space occupied by a substance or object.

W

W and Z bosons Elementary particles that mediate the weak interaction. They are massive and carry electric charge (W⁺, W⁻) or are neutral (Z⁰).

watt (W) The SI derived unit of power, defined as one joule per second. It measures the rate of energy transfer or conversion.

wave A disturbance that propagates through space and time, transferring energy without a net transfer of matter.

wave equation A partial differential equation that describes the behavior of waves.

wave function In quantum mechanics, a mathematical function that describes the quantum state of a system. The square of its magnitude gives the probability density of finding a particle at a particular location.

wave function collapse The apparent instantaneous change of the wave function of a quantum system from one state to another, typically occurring upon measurement.

wave–particle duality The concept that all quantum entities exhibit both wave-like and particle-like properties.

wavelength The spatial period of a wave, the distance over which the wave's shape repeats.

weak interaction One of the four fundamental forces, responsible for processes like radioactive beta decay and nuclear fusion in stars. It acts over very short distances.

weber (Wb) The SI unit of magnetic flux.

wedge A simple machine, essentially a portable inclined plane, used for splitting, lifting, or holding objects apart.

weight The force exerted on an object due to gravity. It is dependent on mass and the local gravitational field strength (Weight = mass × gravitational acceleration).

wheel and axle A simple machine consisting of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other.

white body An idealized object that reflects all incident electromagnetic radiation perfectly and diffusely. The opposite of a black body.

wind The bulk movement of air in the atmosphere, driven by pressure differences.

work In physics, work is done when a force causes a displacement. It is calculated as the product of force and displacement in the direction of the force. Measured in joules.

work function The minimum thermodynamic work (energy) needed to remove an electron from the surface of a solid conductor to a point in the vacuum immediately outside the solid.

X

X-ray A form of high-energy electromagnetic radiation with wavelengths shorter than ultraviolet light and longer than gamma rays. They can penetrate soft tissues but are absorbed by denser materials like bone.

Y

Young’s modulus A measure of the stiffness of a solid material, defined as the ratio of tensile stress to tensile strain in the elastic region of deformation. It quantifies resistance to stretching or compression.

Z

Zeeman effect The splitting of atomic spectral lines into several components when the light source is placed in a magnetic field. This effect provides insights into atomic structure and magnetic fields.

Glossary Of Physics

Contents

Branches of Physics

Research

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

See also