Browse All 842 Physics Terms A–Z

Gravitational Constant Foundations of Physics N·m²/kg² The empirical physical constant relating the gravitational force between two masses to their product and inverse-square separation. G = 6.67430 × 10⁻¹¹ N·m²/kg²

Gravitational Lensing Astrophysics, Cosmology & Relativity Arcseconds (Angular Deflection) The bending of light rays from a background astronomical source around a massive foreground object acting as a gravitational lens. θ_deflection = (4 G M) / (c² b)

Gravitational Mass Foundations of Physics kg A measure of the strength of the gravitational force exerted or experienced by an object in a gravitational field. m = F_g / g

Gravitational Time Dilation Astrophysics, Cosmology & Relativity Seconds (Relativistic Time Difference) The phenomenon where time passes measurably slower in regions of lower gravitational potential (stronger gravity). t_0 = t_f √(1 - 2 G M / (r c²))

Gravitational Waves Astrophysics, Cosmology & Relativity Dimensionless Strain h (10⁻²¹) Ripples in the curvature of spacetime that propagate outward as transverse waves at the speed of light, generated by accelerating asymmetric mass distributions. h_ij = (2 G / (c⁴ r)) (d²I_ij / dt²), Strain h = ΔL / L ~ 10⁻²¹

Gravity Classical Mechanics N The universal attractive force between masses, causing mutual acceleration proportional to mass and inversely proportional to squared distance. Fg = G m1 m2 / r²

Great Attractor Astrophysics, Cosmology & Relativity M_☉ (Gravitational Anomaly Mass) A massive gravitational anomaly in intergalactic space at the center of the Laniakea Supercluster pulling galaxies across hundreds of millions of light-years. v_peculiar ~ 600 km/s towards Laniakea Supercluster center

Green's Function Mathematical & Computational Physics Impulse Response Function An impulse response function used to solve inhomogeneous linear differential equations subject to specified boundary conditions. L G(x, x') = δ(x - x'), y(x) = ∫ G(x, x') f(x') dx'

Green's Theorem Mathematical & Computational Physics 2D Vector Integral Theorem A 2D vector calculus theorem relating a line integral around a simple closed curve C to a double area integral over the enclosed plane region D. ∮_C (L dx + M dy) = ∬_D ((∂M/∂x) - (∂L/∂y)) dx dy

Greenhouse Effect Geophysics & Environmental Physics °C or Kelvin (Warming Effect) The thermodynamic warming process by which atmospheric greenhouse gases absorb outgoing infrared terrestrial radiation and re-emit it in all directions, raising surface temperatures. T_surface = T_effective (1 + ¾ τ_IR)^(1/4) (Radiative Equilibrium)

Group Theory Mathematical & Computational Physics Symmetry Groups (SO(3), SU(2), SU(3)) The mathematical study of groups and algebraic symmetry structures. Group Axioms: Closure, Associativity, Identity, Inverse

Group Velocity Waves, Oscillations & Acoustics m/s The velocity at which the overall envelope shape of a wave packet travels through space, representing energy transport speed. v_g = dω / dk

Gutenberg Discontinuity Geophysics & Environmental Physics km (Boundary Depth) The major geophysical boundary located at a depth of ~2,890 km marking the sharp transition between Earth's solid mantle and liquid outer core. Depth z ≈ 2890 km (Core-Mantle Boundary D'' Layer)

Gyroradius & Cyclotron Frequency Plasma Physics m (Larmor Radius) & rad/s (Cyclotron Frequency) The helical orbital radius (Larmor radius r_L) and angular frequency (cyclotron frequency ω_c) of a charged particle orbiting a magnetic field line. r_L = (m v_⊥) / (|q| B), ω_c = (|q| B) / m

H-mode Confinement Plasma Physics s (Energy Confinement Time τ_E) High-confinement operating regime in tokamaks characterized by a steep edge pressure barrier (pedestal) and doubled energy confinement time. Energy Confinement Time τ_E(H-mode) ≈ 2 × τ_E(L-mode)

Hadrons Nuclear & Particle Physics Composite Particle Class Subatomic composite particles made of quarks and gluons held together by the strong nuclear force. Strongly interacting composite particles (Baryons & Mesons)

Half-Life Nuclear & Particle Physics Seconds, Hours, or Years The time required for half the radioactive nuclei in a given sample to undergo spontaneous radioactive decay. t_½ = ln(2) / λ ≈ 0.693 / λ, N(t) = N₀ (½)^(t / t_½)

Hall Effect Electromagnetism & Electronics V (Hall Voltage), m³/C (Hall Coefficient) The production of a transverse electric potential difference (Hall voltage) across a current-carrying conductor in an orthogonal magnetic field. V_H = (I B) / (n q t), R_H = 1 / (n q)

Hall Effect Thruster Plasma Physics N or mN (Thrust) & s (Specific Impulse ~1500–3000 s) A electric space propulsion plasma engine that accelerates ions across an electrostatic potential drop using trapped electrons in an annular magnetic field. F_thrust = ṁ v_exhaust, v_ex = √(2 e V_acc / m_ion)

Hamiltonian Formalism Mathematical & Computational Physics Joules (Energy) A formulation of classical mechanics describing system dynamics in 2N-dimensional phase space using position q_i and canonical momentum p_i. H(q, p, t) = ∑ p_i q̇_i - L, q̇_i = ∂H / ∂p_i, ṗ_i = -∂H / ∂q_i

Hardness Condensed Matter & Materials Physics MPa or GPa (Mohs scale 1 to 10) A material's resistance to localized plastic surface deformation induced by mechanical scratching, abrasion, or indentation. H = Load / Indentation Surface Area (Mohs, Vickers, Rockwell)

Harmonics Waves, Oscillations & Acoustics Hz Resonant frequencies of a system that are integer multiples of its fundamental frequency. f_n = n f1 (where n = 1, 2, 3, ...)

Hawking Radiation Astrophysics, Cosmology & Relativity Kelvin (Blackbody Temperature T_H) Thermal blackbody radiation predicted to be emitted by black holes due to quantum field fluctuations near the event horizon. T_H = ℏ c³ / (8 π G M k_B), P = ℏ c⁶ / (15360 π G² M²)

Heat Engine Thermodynamics & Statistical Physics W (J/s) A physical device that converts thermal energy absorbed from a high-temperature heat source into mechanical work, discharging waste heat to a cold sink. W = Q_hot - Q_cold, η = W / Q_hot

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