Physics terms starting with P

Polar Coordinates Foundations of Physics m, rad A 2D coordinate system specifying point location by radial distance r from the origin and angular displacement θ from a reference axis. x = r cos θ, y = r sin θ, r = √(x² + y²)

Polarization Optics N/A The property of transverse electromagnetic waves specifying the geometric orientation of their electric field vector oscillations in space. E(z,t) = E0 cos(k z - ω t) i_hat

Polaron Condensed Matter & Materials Physics Quasiparticle Mass A composite quasiparticle consisting of a conduction electron (or hole) bound together with its surrounding self-induced lattice polarization distortion cloud in an ionic crystal. m*_polaron = m* (1 + α_coupling / 6)

Population Inversion Quantum & Atomic Physics Dimensionless Condition A non-equilibrium state of a quantum system where more atoms reside in a higher excited energy state than in lower energy states. N₂ > N₁ (Excited state density > Ground state density)

Positron Emission Tomography (PET Scan) Biophysics & Medical Physics MBq (Activity) & Standardized Uptake Value (SUV) A 3D nuclear medicine imaging technique detecting pairs of 511 keV gamma photons emitted during positron annihilation to map metabolic activity. Coincidence Detection of 180° Back-to-Back 511 keV Gamma Photons

Potential Energy Classical Mechanics J The stored energy an object possesses due to its relative position in a conservative force field or its structural deformation. PE_grav = m g h, PE_elastic = ½ k x²

Power Classical Mechanics W (J/s) The rate at which work is performed or energy is transferred per unit time. P = dW/dt = F · v

Power Factor Electromagnetism & Electronics Dimensionless (0 to 1) The ratio of real power dissipated by an AC circuit to the apparent power delivered by the supply. PF = cos φ = P_real / S_apparent = R / Z

Poynting Vector Electromagnetism & Electronics W/m² (Watts per square meter) A vector representing the directional energy flux density (power per unit area) transported by an electromagnetic field. S = (1 / μ₀) (E × B)

Precession of the Equinoxes Geophysics & Environmental Physics Years per Cycle (~25,800 years) The slow continuous conical rotation of Earth's rotational axis in space, taking ~25,800 years to complete one full cycle. Precession Period T ≈ 25,772 years (Axial Wobble Rate ~ 50.3″/year)

Precision Foundations of Physics Various The degree of agreement or repeatability among independent measurements of the same quantity taken under identical conditions. Standard Deviation (σ)

Presbyopia Optics Diopters (D) The age-related loss of accommodation power in the human eye caused by reduced elasticity of the crystalline lens. Near Point > 25 cm (increases with age)

Pressure Foundations of Physics Pa The perpendicular force exerted per unit surface area over which that force is distributed. P = F / A

Principal Quantum Number Quantum & Atomic Physics Dimensionless Integer The primary quantum number designating the main electron shell, overall orbital size, and principal energy level of an electron in an atom. n = 1, 2, 3, 4...

Principle of Mixtures Thermodynamics & Statistical Physics J The heat conservation principle stating that in an isolated system, heat lost by hotter components equals heat gained by cooler components until equilibrium is reached. ∑ Q = 0 ⇒ ∑ m_i c_i (T_f - T_i) = 0

Principle of Superposition Waves, Oscillations & Acoustics m The principle stating that when two or more linear waves overlap at a point, total resultant displacement equals vector sum of individual displacements. y_total(x,t) = y1(x,t) + y2(x,t) + ... + yn(x,t)

Probability Density Quantum & Atomic Physics m⁻¹ (1D) or m⁻³ (3D) The probability per unit volume of finding a quantum particle at a specific spatial position at a given time. P(x) = |ψ(x, t)|² = ψ*(x, t) ψ(x, t)

Projectile Motion Classical Mechanics m, m/s The 2D motion of an object launched into a gravitational field under the sole influence of gravity (ignoring air resistance). x(t) = v0 cos θ t, y(t) = v0 sin θ t - ½ g t²

Proper Time Astrophysics, Cosmology & Relativity Seconds (Proper Time τ) The physical time interval measured by a clock moving along a specific worldline through spacetime. dτ = dt / γ = √(dt² - dx²/c²)

Protein Folding Biophysics & Medical Physics kJ/mol (Conformational Stability) The physical process by which a polypeptide chain folds spontaneously into a characteristic 3D functional native structure. Energy Funnel Concept: Minimizing Native State Free Energy G

Proton Therapy Biophysics & Medical Physics MeV (Proton Beam Energy ~70–250 MeV) An advanced form of external beam radiation therapy utilizing accelerated proton beams to destroy cancerous tumors. Bragg Peak Energy Deposition Curve: (-dE/dx) ∝ 1 / v²

Protostar Astrophysics, Cosmology & Relativity Solar Masses & Years An early evolutionary mass phase of a star formed by the gravitational contraction of an interstellar gas cloud before core hydrogen fusion ignites. t_collapse ~ t_freefall = √(3π / (32 G ρ))

Pulsar Astrophysics, Cosmology & Relativity Milliseconds to Seconds (Rotation Period) A highly magnetized, rapidly rotating neutron star that emits focused beams of electromagnetic radiation from its magnetic poles. P_spin ~ 1.4 ms to 10 s, P_dot = dP / dt

Pulse Oximetry Biophysics & Medical Physics Percentage (% SpO₂) A non-invasive medical monitoring method measuring arterial blood oxygen saturation (SpO₂) using differential optical absorption of red and infrared light. Ratio R = (AC₆₆₀/DC₆₆₀) / (AC₉₄₀/DC₉₄₀) ⇒ % SpO₂

Terms starting with P