Browse All 842 Physics Terms A–Z

Coulomb's Law Electromagnetism & Electronics N (Newtons) An inverse-square law stating that the electrostatic force between two stationary point charges is directly proportional to the product of their charges and inversely proportional to the square of their… F = k_e |q₁ q₂| / r² = (1 / (4π ε₀)) |q₁ q₂| / r²

Couple Classical Mechanics N·m A system of two equal, parallel forces acting in opposite directions whose lines of action do not coincide, producing pure torque without net linear force. τ = F d

Coupling Constant Nuclear & Particle Physics Dimensionless Parameter A dimensionless number quantifying the relative interaction strength between particles or fields in a fundamental force interaction. α_EM = e² / (4π ε₀ ℏ c) ≈ 1 / 137, α_s(Q²)

Creep Condensed Matter & Materials Physics s⁻¹ (Creep Strain Rate) The slow, time-dependent permanent plastic deformation of a solid material subjected to long-term mechanical stresses below its yield strength, accelerated at elevated temperatures. ε_creep = A σ^n e^(-Q / (R T)) (Power law creep)

Critical Angle Optics Degrees (°) The specific angle of incidence in an optically denser medium for which the angle of refraction in the rarer medium is exactly 90 degrees. θ_c = arcsin(n2 / n1)

Critical Mass Nuclear & Particle Physics kg (Kilograms) The minimum mass of fissile material required to sustain a continuous self-sustaining nuclear chain reaction. Neutron Leakage Rate = Neutron Production Rate (k = 1)

Critical Point Thermodynamics & Statistical Physics Pa, K The endpoint of a phase equilibrium curve in a P-T phase diagram where coexisting liquid and vapor phases become indistinguishable. (∂P/∂V)_T = 0, (∂²P/∂V²)_T = 0

Cryosphere Geophysics & Environmental Physics km² (Spatial Extent) or Gt (Mass) The collective portion of Earth's surface where water exists in solid frozen form. Components: Sea Ice, Glaciers, Ice Sheets, Permafrost, Snow Cover

Crystal Structure Condensed Matter & Materials Physics Å or nm (Lattice Parameters a, b, c) The ordered, periodic three-dimensional arrangement of atoms, ions, or molecules in a crystalline solid. Crystal Structure = Lattice + Basis

Curie-Weiss Law Condensed Matter & Materials Physics Dimensionless (Magnetic Susceptibility) A thermodynamic law describing the magnetic susceptibility of a ferromagnetic or antiferromagnetic material in its paramagnetic phase above the Curie temperature T_C. χ_m = C / (T - T_C) (for T > T_C)

Curl Mathematical & Computational Physics [Vector Field Unit] / m A vector differential operator measuring the local circulation or rotation density of a 3D vector field around a point. curl F = ∇ × F = det|[î, ĵ, k̂], [∂/∂x, ∂/∂y, ∂/∂z], [F_x, F_y, F_z]|

Curve Fitting Mathematical & Computational Physics Goodness of Fit χ² The mathematical construction of a function that best matches a set of experimental data points according to statistical criteria. Minimizing χ² = ∑ ((y_i - f(x_i, θ)) / σ_i)²

Cyclotron Electromagnetism & Electronics Hz (Frequency), J or MeV (Kinetic Energy) A particle accelerator in which charged particles orbit spirally in a constant magnetic field while high-frequency AC electric fields accelerate them twice per turn. f_c = (q B) / (2π m), KE_max = (q² B² R²) / (2 m)

Cyclotron & Synchrotron Emission Plasma Physics W (Radiated Power) Electromagnetic radiation emitted by charged particles undergoing gyromotion acceleration around magnetic field lines in a plasma. P_rad = (2 e⁴ B² v_⊥²) / (3 m_e² c³) (Non-relativistic Cyclotron)

Cyclotron (Particle Physics) Nuclear & Particle Physics MeV (Beam Energy) A circular particle accelerator using a perpendicular magnetic field to bend charged particles into spiral paths while high-frequency AC electric fields accelerate them. f_c = (q B) / (2π m), KE_max = (q² B² R²) / (2 m)

Cylindrical Coordinates Foundations of Physics m, rad, m A 3D coordinate system combining 2D polar coordinates (r, θ) in the transverse plane with a linear vertical height axis z. x = r cos θ, y = r sin θ, z = z

Cytoskeleton Mechanics Biophysics & Medical Physics pN·μm² (Bending Stiffness) The study of the mechanical properties, viscoelasticity, and force generation of the intracellular filament network (actin, microtubules, intermediate filaments). Flexural Rigidity EI = E_young × I_area_moment

Damped Oscillations Waves, Oscillations & Acoustics m Oscillatory motion whose mechanical energy and amplitude decrease exponentially over time due to dissipative forces like friction or viscosity. x(t) = A exp(-b t / 2m) cos(ω_d t + φ)

Darcy's Law Geophysics & Environmental Physics m/s (Darcy Flux q) A foundational hydrogeological equation describing the flow rate of fluid through a porous medium under a hydraulic gradient. Q = -K A (dh / dl), q = Q / A = -K ∇h

Dark Energy Astrophysics, Cosmology & Relativity Cosmological Constant Λ (J/m³) An unknown form of energy with negative pressure that permeates all space and drives the accelerated expansion of the universe. Ω_Λ ≈ 0.68, w = P / ρ ≈ -1

Dark Matter Astrophysics, Cosmology & Relativity M_☉ or kg (Cosmological Density) A non-baryonic form of matter that does not absorb, reflect, or emit electromagnetic radiation, detectable solely through its gravitational effects. Ω_dm ≈ 0.27 (27% of total cosmic mass-energy)

Dark Matter Halo Astrophysics, Cosmology & Relativity kpc (Halo Radius) & M_☉ (Halo Mass) An extended, nearly spherical region of dark matter enveloping a galaxy or galaxy cluster that extends far beyond the visible stellar disk. NFW Density Profile: ρ(r) = ρ₀ / ((r/r_s) (1 + r/r_s)²)

Davisson-Germer Experiment Quantum & Atomic Physics nm (Wavelength) A 1927 physics experiment that experimentally confirmed De Broglie's matter wave hypothesis by demonstrating electron diffraction from a nickel crystal. n λ = 2 d sin θ = h / p

De Broglie Wavelength Quantum & Atomic Physics m or nm (Wavelength) The wavelength associated with a massive particle, expressing its intrinsic wave-like character. λ = h / p = h / (m v)

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