Physics terms starting with S

Significant Figures Foundations of Physics Dimensionless The digits in a measured or calculated quantity that carry meaningful contribution to its measurement precision.

Simple Harmonic Motion Classical Mechanics m, rad/s Repetitive periodic motion where restoring force is directly proportional to displacement and acts toward the equilibrium position. x(t) = A cos(ω t + φ), ω = √(k/m)

Simple Machine Classical Mechanics Dimensionless A basic mechanical device that changes the direction or magnitude of an applied force. MA = F_out / F_in

Simple Microscope Optics Dimensionless (×) An optical magnifying instrument consisting of a single converging biconvex lens used to produce an enlarged, upright, virtual image. M = 1 + (D / f) (Image at near point D)

Singularity Astrophysics, Cosmology & Relativity Infinite Curvature / Density A region in spacetime where gravitational curvature and density become infinite, causing classical general relativity equations to break down. Lim (r → 0): R_μνρσ R^μνρσ → ∞

Solar Wind Plasma Physics km/s (Velocity) & cm⁻³ (Density) A continuous supersonic stream of fully ionized magnetoplasma (protons, electrons, alpha particles) expanding outward from the Sun's corona into interstellar space. v_sw ≈ 300–800 km/s, n_e ≈ 5 cm⁻³ at 1 AU

Solar Wind Interaction Geophysics & Environmental Physics Plasma Density & Velocity The plasma physics interaction between the Sun's supersonic coronal plasma stream and Earth's geomagnetic field. Bow Shock Formation (Supersonic Magnetosheath Plasma Flow)

Solenoid Electromagnetism & Electronics T (Tesla) A long helical coil of insulated wire that produces a uniform interior magnetic field when an electric current flows through it. B = μ₀ n I (where n = N / L)

Sonar Waves, Oscillations & Acoustics m Sound Navigation and Ranging—a technique utilizing acoustic wave propagation underwater to navigate, communicate, or detect objects. d = v_water t / 2

Sonic Boom Waves, Oscillations & Acoustics dB / Pa An explosive impulsive acoustic thunderclap heard on the ground when an object travels faster than the speed of sound. sin α = 1 / M (Mach Cone Angle)

Sound Intensity Waves, Oscillations & Acoustics W/m² The time-averaged rate of sound energy flow per unit area perpendicular to the direction of propagation. I = P / A = p_rms² / (ρ v)

Spacetime Continuum Astrophysics, Cosmology & Relativity 4D Manifold (3 Space + 1 Time) A 4D mathematical continuum combining 3D space and 1D time into a unified pseudo-Riemannian manifold. ds² = g_μν dx^μ dx^ν (4D Pseudo-Riemannian Manifold)

Spark Chamber Nuclear & Particle Physics Visual Spark Tracks A historic particle detector consisting of parallel metal plates filled with noble gas where high-voltage electrical sparks form along ionized particle tracks. High Voltage Spark Discharge along Ionized Tracks

Special Relativity Astrophysics, Cosmology & Relativity Theoretical Framework Albert Einstein's 1905 theory describing the physical behavior of space and time for observers moving in uniform non-accelerated inertial frames. E² = (p c)² + (m₀ c²)², γ = 1 / √(1 - v²/c²)

Specific Humidity Geophysics & Environmental Physics g/kg (Grams of Water Vapor per kg of Air) The mass ratio of water vapor contained within an air parcel relative to the total mass of the moist air parcel. q = m_v / (m_v + m_d) ≈ 0.622 e / P

SPECT Scan Biophysics & Medical Physics MBq (Activity) & Hounsfield-like Functional Units Single-Photon Emission Computed Tomography (SPECT), a nuclear medicine 3D functional imaging technique using gamma-emitting radioisotopes. Gamma Camera 3D Tomographic Reconstruction

Speed of Light Foundations of Physics m/s The maximum speed at which all massless particles, electromagnetic waves, and information travel through a vacuum. c = 299,792,458 m/s

Speed of Sound Waves, Oscillations & Acoustics m/s The speed at which a pressure wave travels through an elastic medium. v = √(K / ρ) (Fluids), v = √(γ R T / M) (Ideal Gas)

Spherical Aberration Optics m An image blur defect in spherical lenses and mirrors where marginal rays focus closer to the element than paraxial central rays. Δf_spherical = f_marginal - f_paraxial

Spherical Harmonics Mathematical & Computational Physics Spherical Surface Functions A set of special orthogonal functions defined on the 2D sphere surface serving as angular solutions to Laplace's equation in 3D spherical coordinates. Y_l,m(θ, φ) = √(((2l+1)/(4π)) ((l-m)!/(l+m)!)) P_l^m(cos θ) e^(i m φ)

Spherical Mirror Optics m A curved mirror having a reflective surface shaped like a section of a sphere, classified as concave (converging) or convex (diverging). 1/f = 1/v + 1/u, f = R/2

Spin Glass Condensed Matter & Materials Physics Disordered Magnetic Phase A disordered magnetic state characterized by random, competing ferromagnetic and antiferromagnetic interactions that freeze atomic spins into a frustrated, non-periodic spatial orientation. Frustrated Exchange Interaction J_ij

Spin-Orbit Coupling Quantum & Atomic Physics eV (Energy Shift) A relativistic quantum interaction between an electron's intrinsic spin magnetic moment and the internal magnetic field created by its orbital motion around the nucleus. H_SO = ξ(r) L · S

Spontaneous Emission Quantum & Atomic Physics s⁻¹ (Transition Rate) The process by which an excited atom or quantum system spontaneously decays to a lower energy state, emitting a photon of random phase and direction. Rate = A₂₁ N₂

Terms starting with S