Physics

Lorentz transformation Linear coordinate transformations linking inertial frames in special relativity; they preserve the spacetime interval and produce time dilation, length contraction, and relativity…

Loudness: perception, measurement and common levels Loudness Loudness is the perceived strength of sound. This article explains how loudness is measured in decibels, how human perception works, common levels, instruments, and health and regu…

Lumen (unit) The lumen (symbol: lm) is the SI derived unit of luminous flux — the perceived power of light — defined as candela times steradian and used to quantify light output and illuminatio…

Luminescence: Non‑thermal Light Emission, Mechanisms and Uses Luminescence Luminescence is light produced without high temperatures. This article summarizes mechanisms (fluorescence, phosphorescence, chemiluminescence, electroluminescence), measurement, a…

Luminiferous aether: historical concept and its role in the development of modern physics Luminiferous aether Luminiferous aether was a 19th‑century hypothesis proposing a medium for light propagation. Experiments and theoretical advances replaced it with field and relativistic description…

Luminous intensity (photometry) Luminous intensity Amount of visible light power emitted by a source in a specific direction per unit solid angle, weighted for human eye sensitivity. SI base unit: candela; used in lighting, display…

M-theory: proposed unifying framework in theoretical physics M-theory Proposed extension of superstring theory that unifies five string theories and 11-dimensional supergravity; mathematically rich but presently lacking direct experimental confirmati…

Mach number: measuring speed relative to the local speed of sound Mach number Mach number expresses an object's speed as a multiple of the local speed of sound. It defines flow regimes (subsonic to hypersonic), depends on temperature, and is widely used in a…

Magnet: properties, types, history, and common uses Magnet Overview of magnets: what they are, how they work, main types, historical notes, and everyday and industrial uses. Includes distinctions like permanent vs electromagnets and magnet…

Magnetic field: properties, origin, and practical applications Magnetic field A magnetic field is the region of space where magnetic forces act. This article explains field lines, sources, measurement, material responses, history, and common applications suc…

Magnetic field line A magnetic field line is a conceptual curve that represents the direction and relative strength of a magnetic field; used for visualization, analysis, and practical mapping of magn…

Magnetic flux Magnetic flux quantifies the amount of magnetic field passing through a surface. It is central to electromagnetic induction, electric machines and magnetic materials; SI unit: the…

Magnetic levitation (maglev): principles, types, and applications Magnetic levitation Magnetic levitation suspends objects using magnetic fields. This article explains basic physics, main methods (EMS, EDS, superconducting, diamagnetic), practical uses and engineeri…

Magnetic moment Quantity that characterizes the strength and orientation of a magnetic source; determines torque in external fields, energy, and dipolar field patterns across scales from electrons…

Magnetic monopoles: theoretical foundations, experimental searches, and implications Magnetic monopole Survey of magnetic monopoles: theory and motivations in particle and grand unified theories, experimental search methods and null results so far, and implications for charge quanti…

Magnetic permeability Magnetic permeability quantifies how a material responds to a magnetic field, relating magnetic flux density and field strength; it varies by material, frequency and field level an…

Magnetic reluctance: concept, formula, and role in magnetic circuits Magnetic reluctance Magnetic reluctance quantifies a material or path's opposition to magnetic flux. It parallels electrical resistance and is central to analysing magnetic circuits, transformers, mot…

Magnetism: Principles, Materials, History and Practical Uses Magnetism Magnetism is a physical phenomenon produced by moving electric charges and intrinsic magnetic moments. This article explains its properties, types of magnetic materials, history, a…

Magnetomotive force: definition, formula, units and applications Magnetomotive force Magnetomotive force (mmf) is the magnetic potential that drives magnetic flux through a magnetic circuit. It is analogous to electromotive force and is commonly measured in ampere-…

Magnetostatics: Principles, Laws, and Applications Magnetostatics Overview of magnetostatics: the study of steady magnetic fields produced by constant currents, its governing laws, practical uses, historical background and important distinctions.

Maser: Microwave Amplification by Stimulated Emission of Radiation Maser A maser is an amplifier or source of coherent microwave-frequency electromagnetic waves produced by stimulated emission. It enabled low-noise amplification, precision clocks and pa…

Mass (physical quantity) Mass Mass is the measure of how much matter an object contains and how it resists acceleration. This article covers definitions, inertial and gravitational mass, measurement methods, hi…

Mass versus weight: understanding the difference Mass versus weight Clear, concise explanation of mass and weight — definitions, units, measurement methods, examples (Earth, Moon, poles), and common confusions between the two.

Mass-to-charge ratio (m/q): definition, units, and role in analysis Mass-to-charge ratio The mass-to-charge ratio (m/q) expresses a particle's mass divided by its electric charge. It governs motion in electromagnetic fields and underpins techniques such as mass spectro…

Material property Overview of material properties: what they are, how they are classified (physical, chemical, intensive/extensive), how they are measured, and why they matter in science and enginee…

Matrix mechanics: the operator formulation of quantum theory Matrix mechanics Matrix mechanics is the original operator-based formulation of quantum theory, using matrices to represent observables and their noncommuting algebra; it remains central to modern…

Matter: Definition, Composition, States, History, and Distinctions Matter Matter is the physical substance that occupies space and has mass. This article explains its composition, common states, historical development, uses, and distinctions from energy,…

Matter wave: wave behavior of particles in quantum theory Matter wave Matter waves describe the wave-like aspects of particles in quantum theory, introduced by de Broglie. They underpin electron diffraction, wavefunctions, and modern quantum instrume…

Maxwell (unit of magnetic flux) Maxwell (unit) The maxwell (symbol: Mx) is the cgs unit of magnetic flux used historically in electromagnetism; 1 Mx = 1 gauss·cm² = 10⁻⁸ weber. It is largely superseded by the SI but remains in…

Maxwell's equations: the fundamental laws of classical electromagnetism Maxwell's equations Concise, accessible account of Maxwell's equations: their content, form, history, physical meaning, and principal consequences for electromagnetic fields, waves, and technology.

Mechanical energy: definition, components, conservation, and applications Mechanical energy Mechanical energy is the sum of kinetic and potential energy in a mechanical system. This article explains its forms, conservation under ideal conditions, common examples, and dist…

Mechanical wave A mechanical wave is a disturbance that travels through a material medium, transmitting energy by local oscillation of particles. Common examples include sound, water waves, seismi…

Mechanics (physics): motion, forces, and material behavior Mechanics Mechanics is the branch of physics that studies motion, forces, energy, and the response of materials, from everyday bodies and machines to fluids, solids and statistical or quantu…

Meissner effect: magnetic field exclusion by superconductors Meissner effect The Meissner effect is the expulsion of magnetic flux from a material when it becomes superconducting, producing flux exclusion, levitation, and key differences from ordinary perfe…

Meson: quark–antiquark hadrons and their role in physics Meson Mesons are hadrons made of a quark and an antiquark. This article summarizes their composition, quantum numbers, types, production and decay, historical role in nuclear theory, and…

Metastability: temporary stability in physics, chemistry, and engineering Metastability Metastability describes states that appear stable but will transition to a more stable configuration after a small disturbance; important across physical sciences, materials, and d…

Metre Convention and the International Bureau of Weights and Measures Metre Convention An overview of the 1875 Metre Convention, the institutions it created, its role in establishing the SI, and its continuing importance for global measurement standards.

Metre per second (m/s) — SI unit of speed and velocity Metre per second The metre per second (m/s) is the SI derived unit for speed and velocity: distance in metres divided by time in seconds. Used in science, engineering and daily measurements; conver…

Metre per second squared (m/s²): unit of acceleration Metre per second squared Standard SI unit for acceleration. Defines change in velocity per time, its notation, interpretation, relation to gravity, conversions, and common uses in physics and engineering.

Michelson interferometer A precision optical instrument that splits and recombines light to measure small distances, wavelengths, refractive indices and phase shifts; central to metrology and the Michelson…

Michelson–Morley experiment: testing the luminiferous aether Michelson–Morley experiment A landmark 1887 interferometer experiment by Albert A. Michelson and Edward Morley that produced a null result for the luminiferous aether and influenced the development of modern…

Mie scattering Exact solution for light scattering by spherical particles. Describes how size, wavelength and refractive index determine scattering, absorption and angular patterns across many fi…

Miles per hour (mph): unit of speed and common usages Miles per hour Miles per hour (mph) is a measure of speed indicating how many miles are traveled in one hour. Commonly used in road signage in the US and UK; convertible to km/h and m/s.

Minkowski spacetime: the four-dimensional geometry of special relativity Minkowski spacetime A concise overview of Minkowski spacetime: its geometry, metric, historical origin, physical meaning, uses in physics, and how it differs from curved spacetime in general relativit…

Moisture: forms, measurement, effects, and control Moisture Moisture is the presence of water in air, soils and materials. This article outlines its forms, measurement methods, effects on environments and structures, and approaches to contr…

Moment (physics): torque, turning effect and applications Moment (physics) A moment (or moment of force) quantifies a force's tendency to rotate a body about a point or axis. Covers definitions, formulas, vector form, units, examples, equilibrium and prac…

Moment of inertia Measure of an object's resistance to changes in its rotation; depends on mass distribution and axis. Expressed in kg·m² and used in mechanics, engineering, and dynamics.

Momentum (linear momentum in classical physics) Momentum Momentum is a vector quantity equal to mass times velocity. This article explains its definition, units, conservation, examples, and related concepts like impulse, collisions, and…