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Mathematical & Computational Physics

Finite Element Method (FEM)

A numerical technique for solving complex partial differential equations by subdividing a large physical domain into smaller, simpler…

K u = f (Global Stiffness Matrix Equation) Numerical Mesh Method
Quantum & Atomic Physics

Finite Potential Well

A quantum potential well model with barriers of finite energy height V₀.

V(x) = V₀ for |x| > a, V(x) = 0 for |x| ≤ a eV or Joules
Thermodynamics & Statistical Physics

First Law of Thermodynamics

A statement of universal energy conservation applied to thermodynamic systems, asserting that internal energy change equals net heat added…

ΔU = Q - W J
Quantum & Atomic Physics

Fluorescence

The rapid absorption of light at a shorter wavelength followed by immediate emission of light at a longer wavelength.

h ν_emitted < h ν_absorbed (Stokes Shift) Nanoseconds (Lifetime)
Biophysics & Medical Physics

Fluorescence Microscopy

An optical microscopy technique utilizing fluorophores excited by specific light wavelengths to image cellular structures with high…

Abbe Diffraction Limit: d_min = λ / (2 NA) ≈ 200 nm nm (Spatial Resolution)
Biophysics & Medical Physics

Fluoroscopy

A dynamic X-ray imaging technique obtaining real-time moving video images of interior anatomical structures and contrast agents.

Real-time continuous low-dose X-ray video acquisition Frames per Second (fps) & Dose Rate (mGy/min)
Plasma Physics

Fokker-Planck Equation for Plasmas

The kinetic equation describing the time evolution of a plasma velocity distribution function subject to small-angle Coulomb collisions.

(∂f / ∂t)_coll = -∇_v · (A f) + ½ ∇_v ∇_v : (B f) Kinetic Collision Operator
Classical Mechanics

Force

A vector interaction that, when unopposed, alters the state of motion or deforms a physical body.

F = m a = dp/dt N (kg·m/s²)
Waves, Oscillations & Acoustics

Forced Oscillations

Oscillations produced in a system subjected to a periodic external driving force.

m (d²x/dt²) + b (dx/dt) + k x = F0 cos(ω t) m
Mathematical & Computational Physics

Fourier Series

An expansion of a periodic function f(x) into an infinite sum of orthogonal sine and cosine harmonic functions.

f(x) = a₀/2 + ∑_(n=1)^(∞) [a_n cos(n x) + b_n sin(n x)] Harmonic Series Expansion
Mathematical & Computational Physics

Fourier Transform

An integral transform that decomposes a continuous time or spatial signal into its constituent frequency or wavevector spectrum.

f̂(k) = ∫_(-∞)^(∞) f(x) e^(-i k x) dx, f(x) = (1 / 2π) ∫_(-∞)^(∞) f̂(k) e^(i k x) dk Inverse Domain Unit (e.g. s⁻¹ or m⁻¹)
Foundations of Physics

Frame of Reference

A coordinate system along with a clock used to record positions, velocities, and times of physical events.

N/A
Quantum & Atomic Physics

Franck-Hertz Experiment

An influential 1914 physics experiment that directly demonstrated the existence of quantized discrete energy states in mercury atoms.

E_loss = h ν = 4.9 eV (for Mercury vapor) eV (Electron-Volts)
Optics

Fraunhofer Diffraction

Far-field wave diffraction where both incident and observed wavefronts are planar, achieved using lenses or large distances.

a sin θ = m λ m
Optics

Fraunhofer Lines

A set of dark absorption lines in the solar spectrum caused by chemical element absorption in the Sun's outer atmosphere.

E = h ν = E_upper - E_lower nm
Waves, Oscillations & Acoustics

Frequency

The number of complete wave cycles or vibrational repetitions occurring per unit time.

f = 1 / T = v / λ Hz (s⁻¹)
Classical Mechanics

Frequency (Mechanics)

The number of complete vibrational cycles occurring per unit time.

f = 1 / T = ω / (2π) Hz (s⁻¹)
Optics

Fresnel Diffraction

Near-field wave diffraction where source or observation screen is close to the diffracting aperture, requiring spherical wavefront…

Fresnel Number F = a² / (λ L) ≳ 1 N/A
Classical Mechanics

Friction

A resistive contact force that opposes relative sliding motion or tendency of motion between surfaces.

fs ≤ μs N, fk = μk N N
Foundations of Physics

Fundamental Constants

Universal physical quantities whose numerical values are constant in space and time throughout the cosmos.

Various
Waves, Oscillations & Acoustics

Fundamental Frequency

The lowest natural frequency at which a standing wave pattern can be established in a vibrating system.

f1 = v / (2 L) (String / Open Pipe) Hz
Astrophysics, Cosmology & Relativity

Galaxy

A massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas, dust, and dark matter.

M_galaxy = v² r / G (includes Dark Matter) Solar Masses (M_☉) and Kiloparsecs (kpc)
Astrophysics, Cosmology & Relativity

Galaxy Cluster

A gravitationally bound structure containing hundreds to thousands of individual galaxies bound together by gravity.

M_total ~ 10¹⁴–10¹⁵ M_☉ (80% Dark Matter, 15% Intracluster Gas, 5% Stars) Megaparsecs (Mpc) & M_☉
Nuclear & Particle Physics

Gamma Decay

A radioactive decay process where an excited atomic nucleus transitions to a lower energy state by emitting a high-energy gamma-ray photon.

ᴬ_Z X* → ᴬ_Z X + γ (High-energy photon emission) MeV or keV (Photon Energy)