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- RadiancePhysical quantity in radiometry
- Radiant energyEnergy carried by electromagnetic or gravitational radiation
- Radiant fluxMeasure of radiant energy over time
- RadiationWaves or particles moving through space
- Radiation pressurePressure exerted upon any surface exposed to electromagnetic radiation
- Radiation protectionRange of safety measures
- Radiative transferEnergy transfer in the form of electromagnetic radiation
- Radio frequencyElectromagnetic frequencies ranging from 3 kHz to 300 GHz
- Radio waveType of electromagnetic radiation
- Radio windowThe radio window is the region of the radio spectrum that penetrate the Earth's atmosphere
- Radioactive decayEmissions from unstable atomic nuclei
- Radioactive sourceRadionuclide emitting ionizing radiation
- Radiogenic nuclideNuclide produced by radioactive conversion from other nuclide
- RadiometryMeasurement of electromagnetic radiation (esp. optical radiation)
- RadionuclideAtom that has excess nuclear energy, making it unstable
- Rainer BlattGerman-Austrian experimental physicist
- Raman scatteringInelastic scattering of photons by matter
- Raman SundrumIndian-American theoretical particle physicist
- Ramanath CowsikIndian astrophysicist
- Ramond–Ramond fieldIn theoretical physics, Ramond–Ramond fields are differential form fields in the 10-dimens
- Rankine cycleModel that is used to predict the performance of steam turbine systems
- Raphael BoussoAmerican physicist
- RapidityMeasure of relativistic velocity
- Rare-earth magnetStrong permanent magnet made from alloys of rare-earth elements
- Ray (optics)Idealized model of light
- Ray tracing (physics)Calculation technique
- Ray transfer matrix analysisRay transfer matrix analysis (also known as ABCD matrix analysis) is a mathematical form f
- Raychaudhuri equationResult in general relativity
- RaylA rayl (symbol Rayl) is one of two units of specific acoustic impedance and characteristic
- Rayleigh problemFluid dynamics problem
- Rayleigh scatteringLight scattering by small particles
- Rayleigh–Jeans lawApproximation of a black body's spectral radiance
- Raymond ChiaoAmerican physicist
- Reaction (physics)Reactive force occurring with every action (Newton's 3rd law of motion)
- Reactive centrifugal forceForce directed away from the center of rotation
- Real gasNon-hypothetical gases whose molecules occupy space and have interactions
- Reciprocal latticeFourier transform of a real-space lattice, important in solid-state physics
- Recrystallization (metallurgy)Process of forming new, defect-free crystal grains within a material
- RedPrimary color
- Redlich–Kwong equation of stateEmpirical algebraic equation of state more precise than the Van der Waals equation
- Reduced massEffective inertial mass
- ReflectanceCapacity of an object to reflect light
- Reflection (physics)"Bouncing back" of waves at an interface
- Reflection coefficientMeasure of wave reflectivity
- Reflection high-energy electron diffractionReflection high-energy electron diffraction (RHEED) is a technique used to characterize th
- RefractionPhysical phenomenon relating to the direction of waves
- Refractive indexProperty in optics
- Refrigerator magnetSmall magnet used to post items on a refrigerator door
- Regge calculusIn general relativity, Regge calculus is a formalism for producing simplicial approximatio
- Regularization (physics)Method used in mathematical physics
- Regulation of nanotechnologyBecause of the ongoing controversy on the implications of nanotechnology, there is signifi
- Reissner–Nordström metricExact solution in general relativity
- Relational quantum mechanicsInterpretation of quantum mechanics
- Relative luminanceRelative luminance follows the photometric definition of luminance including spectral weig
- Relative permittivityMeasure of the electric polarizability of a dielectric, compared with that of a vacuum
- Relative velocityVelocity measured relative to an observer
- Relativistic diskIn general relativity, the relativistic disk expression refers to a class of axi-symmetric
- Relativistic Doppler effectScientific phenomenon
- Relativistic electromagnetismPhysical phenomenon in electromagnetic field theory
- Relativistic Heavy Ion ColliderParticle accelerator at Brookhaven National Laboratory in Upton, New York, USA
- Relativistic mechanicsTheory of motion and forces for objects close to the speed of light
- Relativistic particleIn particle physics, a relativistic particle is an elementary particle with kinetic energy
- Relativistic quantum mechanicsQuantum mechanics taking into account particles near or at the speed of light
- Relativity of simultaneityPhysics principle that simultaneity depends on choice of reference frame
- Relaxation (physics)Return of a perturbed system into equilibrium
- Renata KalloshTheoretical physicist
- RenormalizationMethod in physics used to deal with infinities
- Renormalization groupConcept in theoretical physics
- Representation theory of the Lorentz groupRepresentation of the symmetry group of spacetime in special relativity
- ResazurinResazurin (7-Hydroxy-3H-phenoxazin-3-one 10-oxide) is a phenoxazine dye that is weakly flu
- ResistProtection used in manufacturing and art
- ResonancePhysical characteristic of oscillating systems
- ResonatorDevice or system that exhibits resonance
- Restoring forcePhysical force acting to bring a system back toward equilibrium
- Resultant forceSingle force representing the combination of all forces acting on a physical body
- Retarded potentialType of potential in electrodynamics
- Retarded timePropagation delay of EM radiation (light)
- Reversible process (thermodynamics)Process whose direction can be reversed
- Reynolds numberRatio of inertial to viscous forces acting on a liquid
- Reynolds transport theorem3D generalization of the Leibniz integral rule
- RGB color modelColor model based on red, green and blue
- RGB color spacesAny additive color space based on the RGB color model
- RGBA color modelRGB color model with an opacity channel
- RheologyStudy of the flow of matter, primarily in a fluid state
- RheometerScientific instrument used to measure fluid flow (rheology)
- RheometryMeasurement of fluid flow
- RhoSeventeenth letter of the Greek alphabet
- Richard ArnowittAmerican physicist (1928–2014)
- Richard CastenAmerican physicist
- Richard Christopher CarringtonEnglish astronomer (1826–1875)
- Richard DalitzRichard Henry Dalitz, FRS (28 February 1925 – 13 January 2006) was an Australian physicist
- Riedel (glass manufacturer)Austrian glassware manufacturer
- Riemann solverA Riemann solver is a numerical method used to solve a Riemann problem. They are heavily u
- Right-hand ruleMnemonic for 3D vectors orientations and rotations
- Rigid bodyPhysical object which does not deform when forces or moments are exerted on it
- Rigid body dynamicsStudy of the effects of forces on undeformable bodies
- Rigid categoryIn category theory, a branch of mathematics, a rigid category is a monoidal category where
- Rigid rotorModel of rotating physical systems
- Rigid transformationMathematical transformation that preserves distances
- Ritz methodIn the study of differential equations, the Ritz method is a direct method to find an appr
- RLC circuitResistor Inductor Capacitor Circuit
- RNS formalismIn string theory, the Ramond–Neveu–Schwarz (RNS) formalism is an approach to formulating s
- Robert BindschadlerAmerican physicist
- Robert BrattainAmerican physicist
- Robert BroutAmerican-born Belgian physicist (1928–2011)
- Robert EmdenJacob Robert Emden (4 March 1862 – 8 October 1940) was a Swiss astrophysicist and meteorol
- Robert H. BrillAmerican academic
- Robert H. DickeAmerican astronomer and physicist (1916–1997)
- Robert Myers (physicist)Canadian physicist
- Robert R. CaldwellRobert R. Caldwell is an American theoretical physicist and professor of physics and astro
- Robert StirlingRobert Stirling (25 October 1790 – 6 June 1878) was a Scottish clergyman and engineer. He
- Roberto CarItalian physicist (born 1947)
- Robin DevenishBritish physicist
- Robustness (computer science)Ability of a computer system to cope with errors during execution
- Rock magnetismStudy of magnetic properties in rocks
- Roller coasterRail-based amusement park ride
- Roller Coaster DataBaseRoller Coaster DataBase (RCDB) is a roller coaster and amusement park database begun in 19
- RollingType of motion which combines translation and rotation with respect to a surface
- Rolling resistanceForce resisting the motion when a body rolls on a surface
- Roman glassAncient glass
- Roman potThe Roman pot is the name of a technique (and of the relevant device) used in accelerator
- Ronald C. DavidsonCanadian physicist, professor and scientific administrator
- Room acousticsRoom acoustics is a subfield of acoustics dealing with the behaviour of sound in enclosed
- Root mean squareSquare root of the mean square
- Rose (color)Color between red and magenta plus its shades
- Rotating reference frameConcept in classical mechanics
- Rotating-wave approximationThe rotating-wave approximation is an approximation used in atom optics and magnetic reson
- RotationMovement of an object which leaves at least one point unchanged
- Rotation around a fixed axisType of motion
- Rotation operator (quantum mechanics)Quantum operator
- Rotational frequencyNumber of rotations per unit time
- Rotational spectroscopySpectroscopy of quantized rotational states of gases
- Rotational transitionIn quantum mechanics, a rotational transition is an abrupt change in angular momentum. Lik
- Rotational–vibrational couplingIn physics, rotational–vibrational coupling occurs when the rotation frequency of a system
- Rotational–vibrational spectroscopyBranch of molecular spectroscopy
- RotonCollective excitation in superfluid helium-4 (a quasiparticle)
- Rotor (electric)Non-stationary part of a rotary electric motor
- Routhian mechanicsFormulation of classical mechanics
- Roy KerrNew Zealand mathematician
- Roy SchwittersAmerican physicist (1944–2023)
- Royal Norwegian Navy MuseumThe Royal Norwegian Navy Museum (Norwegian: Marinemuseet) is a museum documenting the hist
- Royal Society of New South WalesThe Royal Society of New South Wales is a learned society based in Sydney, Australia. The
- Ruby (color)Color that represents the ruby gemstone
- Ruby pressure scaleThe ruby fluorescence pressure scale is an optical method to measure pressure within a sam
- Rudolf KohlrauschRudolf Hermann Arndt Kohlrausch (November 6, 1809 in Göttingen – March 8, 1858 in Erlangen
- Rudolf PeierlsGerman-born British physicist (1907–1995)
- Rule of thumbApproximate method for doing something
- Russell J. DonnellyCanadian-American physicist (1930–2015)
- Russian Tsunami Warning SystemEmergency warning system in the Russian Far East
- Rutherford model1911 theoretical description of an atom
- Rutherford scattering experimentsExperiments proving existence of atomic nuclei
- Ryan RohmAmerican string theorist
- RYB color modelSubtractive color model
- Rydberg constantPhysical constants of energy and wavenumber
- Rydberg formulaFormula for spectral line wavelengths in alkali metals
- Rydberg matterRydberg matter is an exotic phase of matter formed by Rydberg atoms; it was predicted arou
