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Foundations of Physics

Significant Figures

The digits in a measured or calculated quantity that carry meaningful contribution to its measurement precision.

Dimensionless Classical Mechanics

Simple Harmonic Motion

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) m, rad/s Classical Mechanics

Simple Machine

A basic mechanical device that changes the direction or magnitude of an applied force.

MA = F_out / F_in Dimensionless Optics

Simple Microscope

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) Dimensionless (×) Astrophysics, Cosmology & Relativity

Singularity

A region in spacetime where gravitational curvature and density become infinite, causing classical general relativity equations to break…

Lim (r → 0): R_μνρσ R^μνρσ → ∞ Infinite Curvature / Density Plasma Physics

Solar Wind

A continuous supersonic stream of fully ionized magnetoplasma (protons, electrons, alpha particles) expanding outward from the Sun's corona…

v_sw ≈ 300–800 km/s, n_e ≈ 5 cm⁻³ at 1 AU km/s (Velocity) & cm⁻³ (Density) Geophysics & Environmental Physics

Solar Wind Interaction

The plasma physics interaction between the Sun's supersonic coronal plasma stream and Earth's geomagnetic field.

Bow Shock Formation (Supersonic Magnetosheath Plasma Flow) Plasma Density & Velocity Electromagnetism & Electronics

Solenoid

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) T (Tesla) Waves, Oscillations & Acoustics

Sonar

Sound Navigation and Ranging—a technique utilizing acoustic wave propagation underwater to navigate, communicate, or detect objects.

d = v_water t / 2 m Waves, Oscillations & Acoustics

Sonic Boom

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) dB / Pa Waves, Oscillations & Acoustics

Sound Intensity

The time-averaged rate of sound energy flow per unit area perpendicular to the direction of propagation.

I = P / A = p_rms² / (ρ v) W/m² Astrophysics, Cosmology & Relativity

Spacetime Continuum

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) 4D Manifold (3 Space + 1 Time) Nuclear & Particle Physics

Spark Chamber

A historic particle detector consisting of parallel metal plates filled with noble gas where high-voltage electrical sparks form along…

High Voltage Spark Discharge along Ionized Tracks Visual Spark Tracks Astrophysics, Cosmology & Relativity

Special Relativity

Albert Einstein's 1905 theory describing the physical behavior of space and time for observers moving in uniform non-accelerated inertial…

E² = (p c)² + (m₀ c²)², γ = 1 / √(1 - v²/c²) Theoretical Framework Geophysics & Environmental Physics

Specific Humidity

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 g/kg (Grams of Water Vapor per kg of Air) Biophysics & Medical Physics

SPECT Scan

Single-Photon Emission Computed Tomography (SPECT), a nuclear medicine 3D functional imaging technique using gamma-emitting radioisotopes.

Gamma Camera 3D Tomographic Reconstruction MBq (Activity) & Hounsfield-like Functional Units Foundations of Physics

Speed of Light

The maximum speed at which all massless particles, electromagnetic waves, and information travel through a vacuum.

c = 299,792,458 m/s m/s Waves, Oscillations & Acoustics

Speed of Sound

The speed at which a pressure wave travels through an elastic medium.

v = √(K / ρ) (Fluids), v = √(γ R T / M) (Ideal Gas) m/s Optics

Spherical Aberration

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 m Mathematical & Computational Physics

Spherical Harmonics

A set of special orthogonal functions defined on the 2D sphere surface serving as angular solutions to Laplace's equation in 3D spherical…

Y_l,m(θ, φ) = √(((2l+1)/(4π)) ((l-m)!/(l+m)!)) P_l^m(cos θ) e^(i m φ) Spherical Surface Functions Optics

Spherical Mirror

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 m Condensed Matter & Materials Physics

Spin Glass

A disordered magnetic state characterized by random, competing ferromagnetic and antiferromagnetic interactions that freeze atomic spins…

Frustrated Exchange Interaction J_ij Disordered Magnetic Phase Quantum & Atomic Physics

Spin-Orbit Coupling

A relativistic quantum interaction between an electron's intrinsic spin magnetic moment and the internal magnetic field created by its…

H_SO = ξ(r) L · S eV (Energy Shift) Quantum & Atomic Physics

Spontaneous Emission

The process by which an excited atom or quantum system spontaneously decays to a lower energy state, emitting a photon of random phase and…

Rate = A₂₁ N₂ s⁻¹ (Transition Rate)