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Glossary of Physics Terms
beginning with letter R
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R Tweet Definition of R Like Definition of R on Facebook
  1. The eighteenth letter of the Appendix:Roman script, English alphabet, preceded by Q and followed by S.
  1. (context, US politics) Republican
    1. (film certification) restricted
    2. reverse
    3. right (as opposed to left)
    4. (context, handbells) ring
    5. (context, baseball, cricket) The statistic reporting the number of runs scored by a player
    6. Thursday
rad Tweet Definition of rad Like Definition of rad on Facebook
  1. (metrology) A non-SI unit of absorbed dose of radiation, equal to 0.01 gray.
  1. (slang) excellent, short for radical
radiant Tweet Definition of radiant Like Definition of radiant on Facebook
  1. A point source from which radiation is emitted.
  2. (astronomy) The apparent origin, in the night sky, of a meteor shower.
  1. Radiate, Radiating light and/or heat.
  2. Emitted as radiation.
  3. Bright, glowing or filled with light.
radiate Tweet Definition of radiate Like Definition of radiate on Facebook
verb (radiat, ing)
  1. To extend, send or spread out from a center like radii.
  2. (transitive) To emit rays or waves.
    • The stove radiates heat.
      1. (intransitive) To come out or proceed in rays or waves.
    • The heat radiates from a stove.
      1. (transitive) To illuminate.
      2. To expose to ionizing radiation, such as by radiography.
      3. (transitive) To manifest oneself in a glowing manner.
      4. (context, ecology, intransitive) to spread into new habitats, migrate.
  1. radiating from a center.
  2. surrounded by rays, such as the head of a saint in a religious picture.
  3. (botany) having parts radiating from the center, such as the petals in many flowers.
  4. (biology) having radial symmetry, such as a seastar.
radiation Tweet Definition of radiation Like Definition of radiation on Facebook
  1. The shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat.
  2. The process of radiating waves or particles.
  3. The transfer of energy via radiation (as opposed to convection or conduction)
  4. Radioactive energy
radiation pressure Tweet Definition of radiation pressure Like Definition of radiation pressure on Facebook
  1. (physics) the pressure exerted by electromagnetic radiation on an object on which it impinges, as a consequence of its momentum
radiative Tweet Definition of radiative Like Definition of radiative on Facebook
  1. (physics) of, relating to, or occuring through radiation
radio Tweet Definition of radio Like Definition of radio on Facebook
  1. (uncountable) The technology that allows for the transmission of sound or other signals by modulation of electromagnetic waves.
  2. (countable) A device that can capture (receive) the signal sent over radio waves and render the modulated signal as sound.
  3. (countable) A device that can transmit radio signal.
  1. To send a message by radio
''I think the boat is sinking, we'd better radio for help.
Usage note: Used for small radio transmitters carried by people, ships, etc, not for regular radio broadcasting to large audiences.
radioactive Tweet Definition of radioactive Like Definition of radioactive on Facebook
  1. Exhibiting radioactivity.
radioactivity Tweet Definition of radioactivity Like Definition of radioactivity on Facebook
  1. Spontaneous emission of radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus.
  2. The radiation so emitted; including gamma rays, alpha particles, neutrons, electrons, positrons, etc.
radioluminescence Tweet Definition of radioluminescence Like Definition of radioluminescence on Facebook
  1. luminescence produced by bombardment with ionizing radiation
radionuclide Tweet Definition of radionuclide Like Definition of radionuclide on Facebook
  1. (physics) a radioactive nuclide
range Tweet Definition of range Like Definition of range on Facebook
  1. Line or series of mountains.
  2. Large fuel-burning stove.
  3. Selection, array. Eg: A range of cars.
  4. Area used for shooting, artillery, etc.
  5. An area of open, often unfenced, grazing land.
  6. (mathematics) The set of values (points) which a function can obtain.
  7. (statistics) The length of the smallest interval which contains all the data. It is calculated by subtracting the smallest observations from the greatest.
  8. The distance to a target, or to the subject of discussion.
We could see the ship at a range of five miles.
  1. (sports) (baseball) The defensive area that a player can cover.
Jones has good for a big man.
  1. (music) Compass - The scale of all the tones a voice or an instrument can produce.
  2. (ecology) The geographical area or zone where a species is normally naturally found.
verb (ranges, ranging, ranged)
  1. (intransitive) (followed by over) To travel over (an area, etc) with a particular purpose.
  2. (intransitive) (mathematics, computing; followed by over) Of a variable, to be able to take any of the values in a specified range.
The variable x ranges over all real values from 0 to 10.
  1. (transitive) classify
rarefaction Tweet Definition of rarefaction Like Definition of rarefaction on Facebook
  1. a reduction in the density of a material, especially that of a fluid
rarefy Tweet Definition of rarefy Like Definition of rarefy on Facebook
verb to rarefy
  1. To make rare, thin, porous, or less dense
  2. To expand or enlarge without adding any new portion of matter to.
reactance Tweet Definition of reactance Like Definition of reactance on Facebook
noun (symbol X)
  1. (context, physics, electric) opposition to the change in flow of current in an alternating current circuit, due to inductance and capacitance; the imaginary part of the impedance
reaction Tweet Definition of reaction Like Definition of reaction on Facebook
  1. An action or statement in response to a stimulus or other event
The announcement of the verdict brought a violent .
You were in the coutroom. What is your ?
When I last tried to eat strawberries I had a terrible allergic .
  1. (chemistry) A transformation in which one or more substances is converted into another by combination or decomposition
    In this , the acid and base will neutralize each other, producing a salt.
recoil Tweet Definition of recoil Like Definition of recoil on Facebook
  1. (context, firearms) The amount of energy transmitted back to the shooter from a firearm which has fired. Recoil is a function of the weight of the weapon, the weight of the projectile, and the speed at which it leaves the muzzle.
verb (recoils, recoiling, recoiled)
  1. To pull back, especially in disgust, horror or astonishment.
He recoiled in disgust when he saw the mess.
Red Tweet Definition of Red Like Definition of Red on Facebook
  1. A Communist
  1. Communist
the Army
regenerate Tweet Definition of regenerate Like Definition of regenerate on Facebook
verb (regenerat, ing)
  1. (transitive) To construct or create anew, especially in an improved manner
  2. (transitive) To revitalize
  3. (context, transitive, biology) To replace lost or damaged tissue
  4. (intransitive) To become reconstructed
  5. (intransitive) To undergo a spiritual rebirth
relative density Tweet Definition of relative density Like Definition of relative density on Facebook
  1. (science)A measure of the density of a material. The ratio of the density of a substance to the density of water at the same temperature. It is dimensionless and therefor has no units.
Typical relative densities (approximate)
: ethanol: 0.79
: water: 1.00
: iron: 7.8
: gold: 19.3
relativistic mass Tweet Definition of relativistic mass Like Definition of relativistic mass on Facebook
  1. (physics) the increased mass of an object moving at relativistic speed relative to an observer
relativity Tweet Definition of relativity Like Definition of relativity on Facebook
  1. the state of being relative to something else.
  1. (physics) the principle (due to Galileo) that the laws of physics should be the same for all observers in uniform motion.
  2. (physics) either of the two principles of special relativity or general relativity (Einstein, Albert Einstein).
repulsion Tweet Definition of repulsion Like Definition of repulsion on Facebook
  1. the act of repelling or the condition of being repelled
  2. an extreme dislike of something, or hostility to something
  1. (physics) the repulsive force acting between bodies of the same electric charge or magnetic polarity
repulsive Tweet Definition of repulsive Like Definition of repulsive on Facebook
  1. tending to rouse aversion or to repulse
  2. (context, physics) having the capacity to repel
residence time Tweet Definition of residence time Like Definition of residence time on Facebook
  1. (hydrology) The average time a particular molecule of water will remain in a body of water.
restitution Tweet Definition of restitution Like Definition of restitution on Facebook
  1. a process of compensation for losses.
rest mass Tweet Definition of rest mass Like Definition of rest mass on Facebook
  1. (physics) the mass of a body when it is not moving relative to an observer
reverberation Tweet Definition of reverberation Like Definition of reverberation on Facebook
  1. A violent oscillation or vibration
    The discomfort caused by the bat's surprised Tommy.
  2. An echo, or a series of overlapping echos
    The that followed Marylin's shout filled the cavern.
  3. An evolving series of effects resulting from a particular event; a repercussion
    Reverberations from the Vietnam war affect our society to this day.
rheology Tweet Definition of rheology Like Definition of rheology on Facebook
  1. (physics) The branch of physics that studies the deformation and flow of matter.
roentgenoscope Tweet Definition of roentgenoscope Like Definition of roentgenoscope on Facebook
  1. a fluoroscope
Rydberg Tweet Definition of Rydberg Like Definition of Rydberg on Facebook
proper noun 
  1. a surname of Swedish origin, derived from ryd, woodland clearing + berg, mountain
  2. w:Johannes Rydberg, Johannes Rydberg Swedish physicist
  3. a lunar impact crater that is located on the far side of the Moon

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