Browse All 842 Physics Terms A–Z

Coefficient of Restitution Classical Mechanics Dimensionless (0 to 1) A fractional measure of elasticity in a collision, defined as ratio of relative separation speed to relative approach speed. e = (v2_f - v1_f) / (v1_i - v2_i)

Cold Atmospheric Pressure Plasma Jet Plasma Physics K (Gas Temperature ~300 K) A non-thermal plasma discharge generated at ambient atmospheric pressure where heavy ions remain near room temperature while free electrons reach high temperatures. T_gas ≈ 300 K (Room Temp), T_electron ~ 10,000–50,000 K

Combining Uncertainties Foundations of Physics Various The mathematical rules used to propagate individual measurement uncertainties into calculated final results. Addition: ΔZ = √(ΔX² + ΔY²); Product: ΔZ/Z = √((ΔX/X)² + (ΔY/Y)²)

Commutator Quantum & Atomic Physics Product Unit of Â and B̂ A mathematical operator evaluating whether two quantum mechanical operators commute with one another. [Â, B̂] = Â B̂ - B̂ Â

Completely Inelastic Collision Classical Mechanics kg·m/s, m/s A collision in which colliding bodies stick together after impact, moving as a single combined mass with maximum kinetic energy loss. m1 v1 + m2 v2 = (m1 + m2) Vf

Complex Analysis Mathematical & Computational Physics Complex Function Theory The branch of mathematical analysis studying functions of complex variables f(z) = u(x,y) + i v(x,y). ∮_C f(z) dz = 2 π i ∑ Res(f, z_k) (Residue Theorem)

Compound Microscope Optics Dimensionless (×) A two-stage optical instrument utilizing a short-focal-length objective lens and a longer-focal-length eyepiece to achieve high magnification. M_total = m_obj × M_eye ≈ (L / f_obj) × (D / f_eye)

Compound Pendulum Waves, Oscillations & Acoustics s A rigid body suspended from a fixed horizontal axis that oscillates under gravity about a pivot point. T = 2π √(I / (m g d))

Compton Effect Quantum & Atomic Physics m or pm (Wavelength Increase) The decrease in energy (increase in wavelength) of an X-ray or gamma-ray photon when scattered by a stationary electron. Δλ = λ' - λ = (h / (m_e c)) (1 - cos θ)

Computed Tomography (CT Scan) Biophysics & Medical Physics Hounsfield Units (HU, Water = 0, Air = -1000, Bone = +1000) A diagnostic medical imaging modality combining rotating X-ray tubes and digital detectors with filtered back-projection algorithms to produce 3D cross-sectional tissue images. Hounsfield Unit HU = 1000 × (μ_tissue - μ_water) / (μ_water - μ_air)

Conduction Band Condensed Matter & Materials Physics eV (Energy Levels) The range of electron energy bands higher than the valence band where electrons are delocalized and free to move throughout the crystal lattice to carry electric current. E ≥ E_c (Populated by free charge carriers)

Conservation of Linear Momentum Classical Mechanics kg·m/s The law stating that total linear momentum of an isolated system remains constant if no net external force acts on it. ∑ p_initial = ∑ p_final

Conservative Force Classical Mechanics N A force for which total work done in moving an object between two points is independent of the path taken. ∮ F · dr = 0, F = -∇ PE

Constructive & Destructive Interference Waves, Oscillations & Acoustics m The phenomenon where overlapping coherent waves combine to reinforce (constructive) or cancel (destructive) each other's amplitude. Path Diff ΔL = m λ (Constructive), ΔL = (m + ½) λ (Destructive)

Continental Drift Geophysics & Environmental Physics Geologic Time Scale (Millions of Years) The historical hypothesis proposed by Alfred Wegener in 1912 stating that Earth's continents were once joined in a single supercontinent (Pangea) before drifting apart. Historical Wegener Hypothesis (Pangea Supercontinent)

Continuity Equation Classical Mechanics m³/s The equation expressing conservation of mass for fluid flow through a pipe or conduit. A1 v1 = A2 v2 = constant (Volumetric Flow Rate Q)

Control Rods Nuclear & Particle Physics Reactivity Control (pcm) Movable rods composed of high-neutron-capture elements (like cadmium, boron, or hafnium) inserted into a nuclear reactor core to regulate chain reaction rates. Neutron Capture Reaction: ¹⁰B + n → ⁷Li + α

Control Variable Foundations of Physics Various Any experimental parameter held strictly constant throughout an investigation to isolate the relationship between independent and dependent variables.

Cosmic Inflation Astrophysics, Cosmology & Relativity Ultra-early Epoch (t ~ 10⁻³⁶ s) A cosmological theory proposing a brief phase of exponential spatial expansion in the early universe (~10⁻³⁶ to 10⁻³² seconds after the Big Bang). a(t) = a₀ e^(H t) (Exponential scale factor growth)

Cosmic Microwave Background (CMB) Astrophysics, Cosmology & Relativity Kelvin (2.725 K Blackbody) The electromagnetic thermal radiation leftover from the recombination epoch of the early universe (~380,000 years after the Big Bang). T_CMB = 2.72548 ± 0.00057 K, λ_peak ≈ 1.06 mm

Cosmic Rays Nuclear & Particle Physics eV or GeV (Particle Energy) High-energy relativistic atomic nuclei and subatomic particles originating from outer space that strike Earth's atmosphere. Primary Energies up to 10²⁰ eV (Extreme Relativistic Protons)

Cosmic Strings Astrophysics, Cosmology & Relativity 1D Topological Defect Hypothetical 1D subatomic-width topological line defects that may have formed during GUT phase transitions in the early universe. Linear Mass Density G μ / c² ~ 10⁻⁶

Cosmological Redshift Astrophysics, Cosmology & Relativity Dimensionless Quantity (z) The stretching of photon wavelengths to longer, redder values as light travels across the expanding space of the universe. z = (λ_observed - λ_emitted) / λ_emitted, 1 + z = a(t_obs) / a(t_emit)

Coulomb Logarithm Plasma Physics Dimensionless Parameter (ln Λ) The natural logarithm of the ratio of maximum to minimum impact parameters in small-angle Coulomb collision integrals. ln Λ = ln(r_max / r_min) = ln(λ_D / b_min) ≈ 10–20

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