Physics terms starting with S

Saha Ionization Equation Plasma Physics m⁻³ (Ionization Balance Density) A thermodynamic relation expressing the ionization state of a plasma in thermal equilibrium as a function of temperature and electron density. (n_i+1 n_e) / n_i = (2 g_i+1 / g_i) (2 π m_e k_B T / h²)^(3/2) e^(-E_ion / (k_B T))

Scalar Foundations of Physics Various A physical quantity that is completely specified by its magnitude (value and unit) alone, possessing no direction.

Scalar Product Foundations of Physics Various An algebraic vector operation that multiplies two vectors to yield a scalar equal to the product of their magnitudes and the cosine of the angle between them. A · B = |A||B| cos θ = Ax Bx + Ay By + Az Bz

Schrödinger Equation Quantum & Atomic Physics Energy (Eigenvalue E in Joules or eV) A fundamental partial differential equation describing how the quantum wave function of a physical system evolves deterministically over time. i ℏ (∂ψ / ∂t) = Ĥ ψ, Ĥ ψ = E ψ

Schwarzschild Radius Astrophysics, Cosmology & Relativity Meters or Kilometers The physical radius defining the event horizon of a non-rotating, spherically symmetric black hole of mass M. R_s = 2 G M / c² ≈ 2.95 km × (M / M_☉)

Scientific Law Foundations of Physics N/A A concise verbal or mathematical statement that describes a universal, consistently observed relationship in nature under specified conditions.

Scientific Method Foundations of Physics N/A An empirical, iterative process for investigating natural phenomena through observation, hypothesis formulation, experimentation, and analysis.

Scientific Notation Foundations of Physics Dimensionless A standardized method of expressing very large or very small numbers in the format a × 10ⁿ, where 1 ≤ |a| < 10 and n is an integer. a × 10^n

Scientific Theory Foundations of Physics N/A A comprehensive, well-substantiated explanation of a broad aspect of nature supported by extensive empirical evidence and repeated testing.

Scintillation Counter Nuclear & Particle Physics Pulse Counts / Energy Spectra A radiation detection instrument that measures ionizing radiation by detecting flashes of light (scintillations) produced in a luminescent material using a photomultiplier tube. Ionizing Radiation → Scintillation Photons → Photoelectrons

Sea Level Rise Geophysics & Environmental Physics mm/year (Rate of Rise) The ongoing increase in global mean sea level caused by thermal expansion of warming ocean water and meltwater input from glaciers and ice sheets. Δh_sea = Δh_thermosteric + Δh_eustatic (Thermal Expansion + Meltwater)

Seafloor Spreading Geophysics & Environmental Physics cm/year (Spreading Rate) The tectonic process occurring at mid-ocean ridges where new oceanic crust is created by upwelling mantle magma and moves laterally away. Spreading Rate v = d / t ~ 2–16 cm/year

Second Law of Thermodynamics Thermodynamics & Statistical Physics J/K The law asserting that spontaneous physical processes increase total entropy in isolated systems, placing fundamental limits on heat engine efficiency. ΔS_total ≥ 0

Seebeck Effect Condensed Matter & Materials Physics μV/K (Seebeck Coefficient S) The direct conversion of a temperature gradient into an electrical voltage across a conductor or semiconductor. V = S ΔT = S (T_hot - T_cold)

Seismic Waves (P & S Waves) Geophysics & Environmental Physics km/s (Seismic Wave Velocities) Elastic body waves that propagate through Earth's interior during an earthquake, classified as Primary (P) waves and Secondary (S) waves. v_P = √((K + ⁴/₃ μ) / ρ), v_S = √(μ / ρ)

Seismology Geophysics & Environmental Physics m/s (Wave Speeds) The scientific study of earthquakes and the propagation of mechanical elastic waves through the Earth's interior and surface layers. v_p = √((K + ⁴/₃ μ) / ρ), v_s = √(μ / ρ)

Selection Rules Quantum & Atomic Physics Dimensionless Quantum Rules A set of quantum mechanical rules constraining allowed radiative transitions between atomic energy states. Δl = ±1, Δm_l = 0, ±1

Self-Inductance Electromagnetism & Electronics H (Henries = V·s/A) The property of an electrical conductor or coil whereby a change in current induces an opposing electromotive force in the conductor itself. E = -L (dI/dt), L = N Φ_B / I

Semiconductor Condensed Matter & Materials Physics S/m (Electrical Conductivity) A class of crystalline solids possessing electrical conductivity between that of conductors and insulators, controllable by temperature, light, or doping. σ = e (n μ_e + p μ_h), n_i = √(N_c N_v) e^(-E_g / (2 k_B T))

Semiconductor Diode Electromagnetism & Electronics A (Current), V (Voltage) A two-terminal semiconductor device formed by a p-n junction that allows electric current to flow easily in one direction while blocking it in reverse. I = I_s [exp(e V / (k_B T)) - 1]

Series Circuit Electromagnetism & Electronics Ω (Ohms) An electrical circuit topology in which components are connected end-to-end sequentially along a single continuous current path. R_total = R₁ + R₂ + R₃, I_total = I₁ = I₂ = I₃

Shape Memory Alloys Condensed Matter & Materials Physics % (Recoverable Superelastic Strain) A class of smart metallic alloys that can be deformed when cold, but return to their original pre-deformed shape when heated above a transition temperature. Reversible Austenite (High T) ↔ Martensite (Low T) Phase Shift

Shock Wave Waves, Oscillations & Acoustics Pa A extremely thin propagating pressure disturbance characterized by a nearly instantaneous jump in pressure, temperature, and density. P2 / P1 = 1 + (2γ / (γ + 1)) (M1² - 1)

SI Units Foundations of Physics Dimensionless The International System of Units (SI), the modern metric system used globally as the standard language of science and measurement.

Terms starting with S