Browse All 842 Physics Terms A–Z

Unit Vector Foundations of Physics Dimensionless A dimensionless vector with a magnitude of exactly one, used exclusively to specify a direction in space. û = u / |u|

Upper & Lower Hybrid Resonances Plasma Physics rad/s (Resonance Frequencies) Characteristic wave resonance frequencies in magnetized plasmas where wave group velocity vanishes and electromagnetic energy couples efficiently into plasma heating. Upper: ω_UH = √(ω_pe² + ω_ce²); Lower: 1 / ω_LH² = 1 / (ω_ci² + ω_pi²) + 1 / (ω_ce ω_ci)

Valence Band Condensed Matter & Materials Physics eV (Energy Levels) The highest range of electron energy bands in a solid that is fully occupied by bound valence electrons at absolute zero temperature. Occupied by valence electrons at T = 0 K

Van der Pol Oscillator Waves, Oscillations & Acoustics N/A A non-linear oscillator with non-linear damping that exhibits stable self-sustained limit cycle vibrations. d²x/dt² - μ (1 - x²) dx/dt + x = 0

Van der Waals Equation Thermodynamics & Statistical Physics Pa·m³ An equation of state modifying the ideal gas law to account for finite molecular volume and attractive intermolecular forces in real gases. (P + a n² / V²) (V - n b) = n R T

Variational Principle Mathematical & Computational Physics Stationary Action Principle A fundamental physical principle asserting that true physical trajectories minimize or render stationary a scalar functional (such as action). δ S = δ ∫_t₁^t₂ L(q, q̇, t) dt = 0 (Hamilton's Principle)

Vector Foundations of Physics Various A physical quantity characterized by both a magnitude and a spatial direction. A = Ax i + Ay j + Az k

Vector Calculus Mathematical & Computational Physics Differential Operators A branch of mathematics dealing with multivariable differentiation and integration of vector fields in 3D Euclidean space. ∇f (Grad), ∇ · F (Div), ∇ × F (Curl), ∇²f (Laplacian)

Vector Components Foundations of Physics Various The scalar projections of a vector along the mutually perpendicular axes of a coordinate system. Ax = A cos θ, Ay = A sin θ

Vector Product Foundations of Physics Various A vector operation multiplying two 3D vectors to yield a vector perpendicular to both, with magnitude equal to the area of the parallelogram they span. A × B = |A||B| sin θ n_hat

Velocity Classical Mechanics m/s A vector quantity expressing the time rate of change of position, possessing both speed and direction. v = dr/dt

Vernier Caliper Foundations of Physics mm A precision measuring instrument utilizing a main scale and a sliding Vernier scale to measure linear dimensions with fine precision. Reading = Main Scale + (Vernier Coincidence × Least Count)

Vibration of Strings Waves, Oscillations & Acoustics Hz (T in N, μ in kg/m) Transverse standing wave resonances produced along stretched flexible strings fixed at both ends. f_n = (n / 2L) √(T / μ), v = √(T / μ)

Virtual Image Optics m An optical image formed where light rays appear to diverge from, but do not actually intersect; cannot be projected on a screen. v < 0 (for virtual image), m > 0 (upright)

Virtual Particles Nuclear & Particle Physics Transient Quantum Fluctuation Transient quantum field fluctuations that mediate interactions between real particles, constrained in lifetime by the energy-time uncertainty principle. ΔE Δt ≥ ℏ / 2, q² ≠ m² c² (Off mass-shell)

Viscosity Classical Mechanics Pa·s (kg/(m·s)) A measure of a fluid's internal resistance to gradual deformation by shear or tensile stress. τ = η (dv/dy)

Visual Angle Optics rad (or arcminutes ') The angle subtended at the eye's nodal point by an object, determining the size of the image formed on the retina. θ ≈ h / d (in radians for small angles)

Vlasov Equation Plasma Physics Collisionless Kinetic Operator The fundamental partial differential equation governing the evolution of the single-particle distribution function f(r, v, t) in a collisionless plasma. ∂f / ∂t + v · ∇_r f + (q / m) (E + v × B) · ∇_v f = 0

Voltage Electromagnetism & Electronics V (Volts = J/C) The electric potential difference between two points, defined as the work required per unit charge to move a positive test charge between them. V = W / q = I R

W and Z Bosons Nuclear & Particle Physics GeV/c² (Rest Mass Energy) Massive elementary vector gauge bosons that mediate the weak nuclear interaction. M_W ≈ 80.38 GeV/c², M_Z ≈ 91.19 GeV/c², Spin = 1

Wadati-Benioff Zone Geophysics & Environmental Physics km (Focal Depth) A planar dipping zone of earthquake foci produced by the subduction of a cold, rigid oceanic lithospheric plate into the mantle. Seismic Focal Depth down to ~670 km along dipping slab

Water Equivalent Thermodynamics & Statistical Physics kg (or g) The mass of water that absorbs or releases the exact same amount of heat as a calorimeter body for an identical temperature change. w = m_cal c_cal / c_water

Wattless Current Electromagnetism & Electronics A (Amperes) The component of alternating current that is 90 degrees out of phase with AC voltage, consuming zero net electrical power. I_wattless = I_rms sin φ

Wave Dispersion Waves, Oscillations & Acoustics N/A The phenomenon where wave phase velocity depends on wave frequency or wavelength in a medium. v_p = f(λ), d²ω/dk² ≠ 0

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