Physics

Fermion: elementary particles that make up matter Fermion Fermions are particles with half-integer spin that obey the Pauli exclusion principle and Fermi–Dirac statistics; they include quarks and leptons and form the constituents of atoms…

Fermionic condensate A fermionic condensate is an ultracold superfluid phase formed when fermions pair and occupy a coherent quantum state; it links cold-atom physics with superconductivity and many-bo…

Ferromagnetism: principles, materials and applications Ferromagnetism Ferromagnetism is a form of magnetic order in which atomic moments align to produce a strong, persistent magnetization. This article describes its origin, properties, common materi…

Feynman diagram: visual language for particle interactions Feynman diagram An accessible overview of Feynman diagrams: what they represent, how to read them, basic rules, historical context, common uses in physics, and their limitations.

Field (physics) A physical field assigns a measurable quantity to every point in space or spacetime. Fields describe forces, distributions and waves in classical and modern physics, from temperatu…

Field strength Field strength is the local magnitude of a physical field; used in classical physics, electromagnetism, differential geometry, and radio engineering to describe intensity and effec…

Filament: elongated structures across physics, astronomy, and biology Filament A filament is a long, threadlike structure found in many fields—from electric lamp wires and laser beams to fungal hyphae and cosmic web strands—sharing shape but differing in scal…

Fire triangle: heat, fuel and oxygen — fundamentals of combustion and control Fire triangle Concise explanation of the fire triangle: the three elements needed for combustion, how removing one extinguishes fire, related control methods, and distinctions such as the fire t…

First law of thermodynamics (conservation of energy) First law of thermodynamics The first law of thermodynamics states that energy cannot be created or destroyed, only transformed. It quantifies exchanges of heat and work and applies to closed systems, underpi…

Fluid (substance that flows and adapts shape) Fluid A fluid is any substance that continuously deforms under shear stress—commonly liquids, gases, and plasmas. Article covers properties, types, behavior, examples, and distinctions f…

Fluid dynamics: principles, history, and applications Fluid dynamics Overview of fluid dynamics: core principles (continuity, momentum, viscosity), historical development, practical applications (aerodynamics, oceanography, medicine), and computatio…

Fluid mechanics: principles, history, and applications Fluid mechanics Study of fluids (liquids and gases), their behavior at rest and in motion, governing principles, historical development, key equations, applications, and modern computational metho…

Fluid statics (hydrostatics): pressure, buoyancy, and equilibrium Fluid statics Study of fluids at rest: pressure distribution, Pascal's law, buoyancy (Archimedes), hydrostatic paradox, measurement methods, and engineering applications such as dams, ships, and…

Fluorescence: light emission by energized materials Fluorescence Fluorescence is the rapid emission of light by a substance that has absorbed electromagnetic energy; used widely in science, medicine, industry, and art for detection, imaging, and…

Flux: concept, definitions, examples, and uses in science and mathematics Flux Flux describes how much of a field, substance, or quantity passes through a surface or region. It appears in physics and mathematics in contexts such as fluids, heat, electricity a…

Flywheel — mechanical energy storage and rotational inertia Flywheel A flywheel is a rotating mass designed to store kinetic energy and stabilise rotational speed. This article covers principles, construction, applications, history, design trade-off…

Focal length: definition, properties, and practical effects Focal length Focal length measures how strongly a lens, mirror or optical system converges or diverges light. It shapes image size, field of view and depth of field in optics and photography.

Focus (optics): image points, limits, and practical implications Focus (optics) In optics, a focus is where light from a point source is brought together to form an image. This article explains how focus is produced, real vs virtual images, practical limits an…

Foot‑pound force (ft·lbf) Foot-pound force A customary unit of energy and of torque equal to one foot multiplied by one pound-force; commonly used in engineering, ballistics and mechanics. Approximately 1.356 joules.

Force (physics): definition, types, and effects Force A concise encyclopedia article on force: its definition in physics, vector nature, contact vs. field forces, Newton’s laws, the four fundamental forces, history, examples, and prac…

Force field — physical fields and fictional energy barriers Force field An overview of the term “force field,” covering its scientific meaning as a physical field that exerts forces (gravity, electric, magnetic, quantum fields) and its use in fiction a…

Foucault pendulum A large pendulum used to demonstrate Earth’s rotation by showing the steady precession of its swing plane; first exhibited by Léon Foucault in 1851 and now common in museums and un…

Frame of reference (physics) Frame of reference A frame of reference is the coordinate system and set of conventions an observer uses to measure positions, velocities and accelerations; choices affect apparent motion and forces.

Frame dragging (Lense–Thirring effect) Frame-dragging Frame dragging is a general relativity prediction: rotating masses drag local spacetime, producing small precessions measurable near Earth and large effects close to compact object…

Free fall (physics) Free fall Free fall: motion under gravity alone. Overview of definition, equations, history, examples (projectiles, skydivers, spacecraft), terminal velocity and distinctions like weightless…

Free-electron laser (FEL): principles, history and applications Free-electron laser A free-electron laser (FEL) is a tunable, high-power light source that uses a relativistic electron beam and a magnetic undulator to generate coherent radiation from microwaves to…

Frequency: concepts, units, and examples in waves and oscillations Frequency Frequency measures how often a repeating event occurs per unit time. This article explains its definition, units, relation to wavelength and speed, examples (sound, light, radio),…

Fresnel lens — design, history and applications Fresnel lens A Fresnel lens is a lightweight, segmented optical lens developed for lighthouses; it allows large apertures and short focal lengths with far less material than conventional lenses…

Friction (resistive force between contacting surfaces) Friction Friction is the resistive force that opposes relative motion between surfaces. It converts mechanical energy to heat and sound, has several types, and is central to engineering, na…

Fundamental force (four fundamental interactions) Fundamental force Overview of the four fundamental forces—gravity, electromagnetism, strong and weak interactions—their carriers, ranges, roles in nature, and modern physics context.

Fusion power: principles, development, and prospects Fusion power A concise, neutral overview of fusion power: how fusion produces energy, main confinement approaches, historical milestones, potential uses, technical challenges, and current resea…

G-force: acceleration relative to gravity and its effects G-Force G-force is acceleration measured relative to Earth's gravity. This article defines g, explains units and measurements, describes physiological effects, and gives examples from avia…

Gamma ray High-energy electromagnetic radiation emitted by atomic nuclei and astrophysical sources; highly penetrating and ionizing, used in medicine, industry and astronomy with important s…

Gas-filled tube: principles, history, types, and applications Gas-filled tube A gas-filled (discharge) tube is an electrical device in an insulated envelope containing gas; when driven by sufficient voltage it conducts, emits light, and finds use in lamps, s…

Gauge boson Particles that mediate fundamental forces in gauge theories. In the Standard Model they include the photon, W and Z bosons, and gluons; a graviton is hypothetical for gravity.

Gauss (unit of magnetic flux density) Gauss (unit) The gauss (G) is the CGS unit of magnetic flux density, equal to one maxwell per square centimetre and equivalent to 10⁻⁴ tesla. Used historically in magnetism, it remains common i…

Gauss's law: statement, meaning, history and applications Gauss's law Gauss's law relates electric charge to electric flux through a closed surface. It appears as an integral and differential equation and is central to electrostatics and Maxwell's eq…

Gauss's law for magnetism One of Maxwell's equations stating the net magnetic flux through any closed surface is zero, implying no isolated magnetic charges (magnetic monopoles) are observed and magnetic fi…

Geiger–Marsden experiment (Gold foil or Rutherford experiment) Geiger–Marsden experiment 1909 laboratory experiment by Hans Geiger and Ernest Marsden under Ernest Rutherford demonstrating the concentrated atomic nucleus by alpha-particle scattering and overturning the…

General relativity: Einstein’s theory of gravitation and spacetime General relativity A concise, neutral overview of general relativity: its core ideas of curved spacetime, main equations, experimental tests, applications (GPS, cosmology), and how it differs from Ne…

Giant magnetoresistance (GMR): principles, history and applications Giant magnetoresistance Giant magnetoresistance (GMR) is a spin-dependent change in electrical resistance in layered magnetic materials, foundational to modern magnetic sensors, hard-disk read heads and s…

Gluon (carrier of the strong interaction) Gluon A gluon is the gauge boson of quantum chromodynamics (QCD). It mediates the strong force between quarks, carries color charge, self-interacts, and underlies the binding of protons…

Grand Unification Theory (GUT): Overview, History, and Significance Grand unification theory Grand unification theory (GUT) seeks to merge the strong, weak and electromagnetic interactions into a single framework. This article explains its ideas, history, experimental test…

Gravitational constant (G): definition, measurement and significance Gravitational constant The gravitational constant G quantifies the strength of Newtonian gravity. This article explains its meaning, units, measurement history, roles in physics, and common confusions su…

Gravitational energy — concepts, formulas, and practical examples Gravitational energy Gravitational energy (gravitational potential energy) is the energy an object has due to its position in a gravitational field. This article explains its forms, formulas, history,…

Gravitational field A gravitational field is the region around mass where gravitational effects are felt. It connects Newtonian gravity with Einstein’s relativity and is measured as acceleration per u…

Gravitational singularity A gravitational (spacetime) singularity is a region where classical general relativity predicts divergent curvature and density; it marks a breakdown of the theory and motivates qu…

Gravitational Waves: Theory, Astrophysical Sources, and Detection Gravitational wave Overview of gravitational waves: the theory from general relativity, astrophysical sources like merging black holes and neutron stars, and detection methods that opened a new obser…