Browse All 842 Physics Terms A–Z

Neutral Beam Injection (NBI) Plasma Physics MW (Beam Power) & keV (Particle Energy ~100–1000 keV) A primary plasma heating and current drive method where high-energy neutral atom beams are injected into a magnetic confinement fusion reactor. P_NBI = I_beam × V_acceleration

Neutrino Nuclear & Particle Physics eV/c² (Mass Limit) An extremely light, electrically neutral spin-1/2 elementary lepton that interacts almost exclusively via the weak nuclear force. m_ν < 0.1 eV/c², Spin = ½, Charge = 0

Neutrino Oscillations Nuclear & Particle Physics Probability (0 to 1) A quantum mechanical phenomenon in which a neutrino created with a specific lepton flavor changes flavor as it propagates through space. P(ν_α → ν_β) = sin²(2θ) sin²(1.27 Δm² L / E)

Neutron Star Astrophysics, Cosmology & Relativity M_☉ (Mass), km (Radius) An ultradense stellar core remnant produced by the core-collapse supernova explosion of a massive star, composed almost entirely of neutrons. M ≈ 1.4–2.1 M_☉, R ≈ 10–12 km, ρ ≈ 10¹⁷ kg/m³

Newton's First Law Classical Mechanics N/A The principle that an object remains at rest or continues in uniform motion in a straight line unless acted upon by a net external force. ∑ F = 0 ⇒ v = constant

Newton's Rings Optics m An interference pattern of concentric bright and dark rings formed by an air film enclosed between a plano-convex lens and a flat glass plate. r_m² = m λ R (Dark rings in reflection)

Newton's Second Law Classical Mechanics N The law stating that net force acting on a body equals the rate of change of its linear momentum, simplified to mass times acceleration for constant mass. F_net = m a

Newton's Third Law Classical Mechanics N The law stating that whenever two objects interact, they exert forces on each other that are equal in magnitude and opposite in direction. F_A_to_B = -F_B_to_A

Nodes & Antinodes Waves, Oscillations & Acoustics m Specific fixed positions on a standing wave where displacement amplitude is zero (nodes) or maximum (antinodes). Node Spacing = λ / 2, Antinode Spacing = λ / 2

Non-conservative Force Classical Mechanics N A force for which work done depends on the specific path taken, dissipating mechanical energy into heat, sound, or internal energy. W_non-cons = ΔME = ΔKE + ΔPE

Non-linear Oscillations Waves, Oscillations & Acoustics Various Oscillatory systems where restoring forces do not obey linear Hooke's law, leading to amplitude-dependent frequency and chaotic behavior. m (d²x/dt²) + k x + β x³ = 0 (Duffing Equation)

Non-Neutral Plasma Plasma Physics Single-Species Charged Cloud A plasma composed exclusively of a single species of charged particles (electrons, positrons, or single ions) without background charge neutralization. n_e ≫ n_i (Pure Electron or Ion Plasma)

Non-Newtonian Fluids Condensed Matter & Materials Physics Pa·s (Apparent Viscosity η) Fluids whose shear viscosity changes depending on applied shear rate, stress magnitude, or shear history. τ = K (du / dy)^n (n ≠ 1)

Nonlinear Dynamics Mathematical & Computational Physics Phase Space Dynamics The study of physical systems governed by non-linear equations where output changes are not directly proportional to input changes. d x / dt = f(x) (where f is non-linear)

Normal Force Classical Mechanics N The perpendicular contact force exerted by a surface on an object pressing against it. N = m g cos θ

Normal Modes Waves, Oscillations & Acoustics Hz Characteristic independent natural patterns of motion in which all parts of an oscillating system move sinusoidally at the same natural frequency. f_n = n f1 = n v / (2 L)

Nuclear Binding Energy Nuclear & Particle Physics MeV (Mega-electronvolts) The minimum energy required to completely disassemble an atomic nucleus into its constituent protons and neutrons. E_b = Δm c² = [Z m_p + (A - Z) m_n - M_nucleus] c²

Nuclear Fission Nuclear & Particle Physics MeV (Mega-electronvolts) A nuclear reaction in which a heavy nucleus splits into two or more smaller daughter nuclei accompanied by the release of neutrons and substantial energy. ¹₀n + ²³⁵₉₂U → ²³⁶₉₂U* → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3 ¹₀n + Q (~200 MeV)

Nuclear Fusion Nuclear & Particle Physics MeV (Mega-electronvolts) A nuclear reaction in which two light atomic nuclei collide and combine to form a single heavier nucleus, releasing vast amounts of energy. ²₁H + ³₁H → ⁴₂He + ¹₀n + 17.6 MeV

Nuclear Reactor Nuclear & Particle Physics MWth or MWe (Power Capacity) An engineered facility in which a controlled self-sustaining nuclear chain reaction is maintained to generate thermal energy for electrical power generation. Multiplication Factor k = Neutrons in generation (i+1) / Neutrons in generation i

Nuclear Shell Model Nuclear & Particle Physics Quantized Energy Shells A quantum nuclear model describing nuclear energy levels in terms of individual nucleons moving inside a central potential well with strong spin-orbit coupling. Magic Numbers: 2, 8, 20, 28, 50, 82, 126

Nuclear Stability Nuclear & Particle Physics Dimensionless N/Z Ratio A measure of a nuclide's resistance to spontaneous radioactive decay, determined by the balance between nuclear strong attraction and proton Coulomb repulsion. N/Z ≈ 1 (for light nuclei), N/Z ≈ 1.5 (for heavy nuclei)

Null Vector Foundations of Physics Various A vector having zero magnitude and an arbitrary or indeterminate direction. 0 = 0i + 0j + 0k

Numerical Linear Algebra Mathematical & Computational Physics Matrix Factorization Algorithms The subfield of numerical analysis studying algorithms for performing matrix operations efficiently and accurately on digital computers. LU: A = L U, QR: A = Q R, SVD: A = U Σ V^T

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