Physics

Thermodynamic potentials: definitions, common forms, and applications Thermodynamic potential An overview of thermodynamic potentials—energy-like functions (U, A, H, G, Ω), their natural variables, how they are formed via Legendre transforms, and their roles in equilibrium…

Thermodynamic state: definition, properties, and significance Thermodynamic state A thermodynamic state describes a system by a set of macroscopic parameters (temperature, pressure, composition, etc.). This article explains how states are specified, their uses,…

Thermodynamic system: definition, types, properties, and applications Thermodynamic system Overview of thermodynamic systems: definitions, boundaries, classifications (isolated, closed, open), key properties, historical context, examples, and practical importance in engi…

Thermodynamics: principles, laws, and applications Thermodynamics Comprehensive overview of thermodynamics: core concepts, laws, systems, statistical foundations, thermodynamic potentials, typical processes, measurement, and common applications a…

Third law of thermodynamics Principle describing the behaviour of entropy as temperature approaches absolute zero and its practical and conceptual consequences in physics and chemistry.

Thou (unit) The thou, also called the mil in the United States, is a unit equal to one thousandth of an inch (0.001 in). Common in machining and manufacturing, it is often used for tolerances…

Three-body problem in classical mechanics Three-body problem The three-body problem asks how three masses move under mutual gravitational attraction. It has no general closed-form solution and is central to celestial mechanics, chaos theory,…

Thrust: definition, measurement, and applications Thrust Thrust is the force that moves a vehicle by accelerating mass in the opposite direction. This article explains its physics, units, history, common applications, and important disti…

Thunder (sound produced by lightning) Thunder Thunder is the audible shock wave produced when lightning rapidly heats and expands air. This article explains how thunder forms, how to estimate distance, safety guidance, and not…

Tidal energy: sources, technologies, history and impacts Tidal energy Tidal energy converts the motion and height differences of tides and ocean currents into electricity. This article explains mechanisms, technologies, history, benefits, limits and…

Tidal force: differential gravity and its effects Tidal force Tidal force is the difference in gravitational pull across an extended body. It shapes ocean tides, causes tidal locking and heating, and influences orbital evolution and planetary…

Time: concept, measurement, and scientific perspectives Time A concise encyclopedia entry on time: what it is, how it is measured, its history, scientific formulation in relativity, and its role in daily life and science.

Time dilation: how motion and gravity alter the passage of time Time dilation Time dilation is the relativistic effect by which elapsed time differs for observers in relative motion or at different gravitational potentials, with practical consequences for sa…

Time-domain spectroscopy: principles, instruments, and applications Time-domain spectroscopy Time-domain spectroscopy records how electromagnetic fields change over time and uses Fourier analysis to recover frequency information; widely used with pulsed sources for materia…

Top quark The top quark is the heaviest known elementary particle, a third‑generation up‑type quark with a very short lifetime, distinctive decays, and an important role in testing the Stand…

Torque (Moment of Force) — Physics and Engineering Overview Torque Torque is the rotational effect of a force about a point or axis. This article explains definitions, formulas, units, history, examples, and distinctions from related concepts.

Torsion (mechanics): twisting of structural members under torque Torsion (mechanics) Torsion is the twisting deformation of a structural member produced by an applied torque. This article explains stress and angle-of-twist formulas, assumptions, practical examples,…

Trajectory (path of motion) Trajectory Trajectory: the path an object follows through space and time; covers definitions, mathematical representation, categories (projectile, orbital, guided), measurement, applications,…

Transonic flight and aerodynamics Transonic Transonic describes the aerodynamic regime around the speed of sound (roughly Mach 0.8–1.2), where mixed subsonic and supersonic flow causes shock waves, increased drag, and specif…

Transparency (optical properties of materials) Transparency Optical transparency: how materials transmit light, why some substances are clear or cloudy, biological transparency, historical development of glass and modern uses in optics and…

Transverse wave A transverse wave is one in which oscillations of the medium or field are perpendicular to the direction of energy propagation; includes waves on strings, light, and seismic S-wave…

Turbulence (fluid dynamics) — chaotic motion in fluids Turbulence Turbulence is the complex, irregular motion of fluids characterized by vortices, energy cascades and strong mixing. It contrasts with laminar flow and affects weather, engineering,…

Twin paradox A clear, concise overview of the twin paradox: the special‑relativity thought experiment, its resolution, historical context, experimental tests, and common misconceptions.

Two-body problem (classical mechanics) Two-body problem The two-body problem describes motion of two masses interacting under mutual forces. It reduces to a one-body problem in relative coordinates and has exact solutions for central in…

Tyndall effect — light scattering that makes beams and colours visible Tyndall effect The Tyndall effect is the scattering of light by particles in a colloid or suspension, producing visible beams and wavelength-dependent colours such as the blue of the sky and blue…

Ultra High Frequency (UHF): properties, history, and common uses Ultra high frequency Ultra High Frequency (UHF) is the 300 MHz–3 GHz portion of the radio spectrum used for TV, mobile, Wi‑Fi, RFID and more; it has characteristic propagation, antenna requirements, an…

Ultraviolet (UV) radiation Ultraviolet Ultraviolet radiation is electromagnetic light with wavelengths shorter than visible violet (about 10–400 nm). It has distinctive physical properties, biological effects, practical…

Ultraviolet catastrophe Failure of classical physics to predict blackbody radiation at high frequencies, resolved by Planck's quantization and foundational to quantum mechanics.

Uncertainty principle Principle in quantum mechanics that limits simultaneous knowledge of certain pairs of physical properties, most famously position and momentum; foundational to modern atomic theory…

Undulator: periodic magnet device for bright, tunable synchrotron radiation Undulator An undulator is a periodic magnet insertion device that forces charged particles to oscillate and emit bright, narrow-band synchrotron radiation. This article explains operation, t…

Physical Measurement and Units: Systems, Standards, and SI Definitions Unit of measurement Overview of physical measurement and units: how systems and standards—including SI definitions, metric and imperial traditions—ensure consistent, reproducible quantities like the m…

Up quark: properties and role in matter Up quark Overview of the up quark, its intrinsic properties, role in protons and neutrons, interactions, historical context and significance in particle physics.

Vacuum (absence or near-absence of matter) Vacuum A vacuum is a region with very low or no matter and reduced pressure. This article explains its physical properties, history, how vacuums are made and measured, and common scientif…

Velocity: vector measure of motion and its significance Velocity Velocity is a vector quantity expressing how fast and in which direction an object moves. This article explains its definition, components, measurement, historical background, and…

Venturi effect: fluid speed, pressure changes, and practical uses Venturi effect The Venturi effect describes how a fluid’s velocity increases and its static pressure decreases when flowing through a constriction, a consequence of mass and energy conservation u…

Vertical: orientation, meanings, and applications Vertical Vertical describes an up–down orientation — perpendicular to the horizontal — and appears across science, mathematics, music, business, engineering, sports and everyday objects.

Vibration: principles, types, measurements and practical importance Vibration Vibration is oscillatory motion about an equilibrium point. This article covers basic properties, types, measurement, mathematical models, engineering concerns, resonance, damping…

Viscosity: how fluids resist flow and why it matters Viscosity Viscosity quantifies a fluid's resistance to flow. This article explains types, units, measurement methods, temperature effects, common examples (water, oils, lava), and key distin…

Visible spectrum: the portion of electromagnetic radiation seen as color Visible spectrum Range of electromagnetic radiation perceptible to human vision, roughly 380–750 nm, covering spectral colors, human perception, measurement, and key applications in optics and spec…

Volt (unit of electric potential) Volt The volt (symbol V) is the SI derived unit of electric potential difference and electromotive force, equal to one joule per coulomb. Named for Alessandro Volta, it underpins electr…

Voltage (Electric Potential Difference) Voltage Voltage, or electric potential difference, is the measure of energy change per unit charge that drives electric current. This article explains definitions, units, types, history, m…

Volume (three-dimensional space occupied) Volume Volume is the measure of three-dimensional space that an object or substance occupies. This article explains definition, measurement methods, common formulas, history, applications…

Vortex: spinning fluid flows — types, physics, and examples Vortex A vortex is a region of fluid that rotates around an axis. This article explains vortex structure, types (free/forced), formation, physical principles, natural examples and enginee…

W and Z bosons: carriers of the weak interaction W and Z bosons W and Z bosons are massive spin-1 gauge particles that mediate the weak nuclear force; W± carry electric charge, Z0 is neutral and its own antiparticle. Discovered at CERN in 1983.

Warm (temperature, sensation, and uses) Warm Warm describes a relative state of higher temperature and the human sensation of mild heat. Covers physical basis, perception, common uses, safety, and distinctions from cool or ho…

Watt — SI unit of power Watt The watt (W) is the SI derived unit of power, equal to one joule per second. It quantifies rate of energy transfer or work and appears in electrical, mechanical and thermal applica…

Wave (oscillation): types, properties, history and applications Wave A wave is a travelling oscillation that transmits energy and information. This article explains wave properties, classifications, historical development, typical behaviors, and com…

Wave (physics): nature, types, properties and applications Wave (physics) An accessible overview of waves in physics: definitions, main types (mechanical, electromagnetic, quantum), key properties, historical milestones, behaviors like interference, and…