Category: Dictionary

stable isotope ratio : The relative abundances of the atomically stable isotopes of a given element as they occur in nature or in a particular experimental context.

speed of light ( c )A fundamental universal physical constant defined as exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time. When not otherwise qualified, the term “speed of light” usually refers to the speed of light in a vacuum, as opposed to the speed of light through some physical medium.

solubility : The tendency of a solid, liquid, or gaseous chemical substance (called a solute) to dissolve in another solid, liquid, or gaseous substance (called a solvent) to form a homogeneous solution of the solute in the solvent. The solubility of a solute fundamentally depends on the specific solvent as well as on temperature and pressure.

siphon : A tube in an inverted U shape that causes a liquid to flow uphill without pumps, powered by the fall of the liquid as it flows down the tube under the pull of gravity. The term may also more generally refer to a wide variety of devices involving the flow of liquids through tubes.

siphon : A tube in an inverted U shape that causes a liquid to flow uphill without pumps, powered by the fall of the liquid as it flows down the tube under the pull of gravity. The term may also more generally refer to a wide variety of devices involving the flow of liquids through tubes.

simple machine : A mechanical device that changes the direction or magnitude of a force. In general, a set of six classical simple machines identified by Renaissance scientists drawing from Greek texts on technology are collectively defined as the simplest mechanisms that can provide mechanical advantage (also called leverage).

Schrödinger equation : A mathematical equation which describes the time evolution of wave functions in quantum mechanics.

shortwave radiation (SW) : Radiant energy of the electromagnetic spectrum with wavelengths in the visible, near-ultraviolet, and near-infrared spectra, the broadest definition of which includes all radiation with a wavelength between 0.1 μm and 5.0 μm.

screw : A mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force; one of six classical simple machines.

science : A systematic enterprise that builds and organises knowledge in the form of testable explanations and predictions about the universe.

scattering : The general physical process by which some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localised non-uniformities in the medium through which they pass.

scalar : Any simple physical quantity that can be described by a single number (as opposed to vectors, tensors, etc., which are described by several numbers such as magnitude and direction) and is unchanged by coordinate system rotations or translations (in Newtonian mechanics) or by Lorentz transformations or central-time translations (in relativity).

Rydberg formula : A formula used in atomic physics to describe the wavelengths of spectral lines of many chemical elements.

rotational speed: Also called speed of revolution.

The number of complete rotations or revolutions a rotating body makes per unit time.

rotational energy: Also called angular kinetic energy.

The kinetic energy due to the rotation of an object, which forms part of its total kinetic energy.

rigid body : An idealization of a solid body in which deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time regardless of the external forces exerted on it. Even though such an object cannot physically exist due to relativity, objects can normally be assumed to be perfectly rigid if they are not moving near the speed of light.

refraction : The change in direction of a wave as it passes from one transmission medium to another or as a result of a gradual change in the medium. Though most commonly used in the context of refraction of light, other waves such as sound waves and fluid waves also experience refraction.

redshift : A phenomenon which occurs when light seen coming from an object that is moving away from the observer is proportionally increased in wavelength or “shifted” to the red end of the visible light spectrum.

radionuclide: Also called a radioactive nuclide, radioisotope, or radioactive isotope.

Any nuclide possessing excess nuclear energy to the point that it is unstable. Such excess energy is emitted through any of several processes of radioactive decay, resulting in a stable nuclide or sometimes another unstable radionuclide which can then undergo further decay. Certain radionuclides occur naturally; many others can be produced artificially in nuclear reactors, cyclotrons, particle accelerators, or radionuclide generators.

quark : An elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.

quantum mechanics : A branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the Planck constant. Quantum mechanics departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales, and provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter that occur at this scale.

quantum field theory : A theoretical framework for constructing quantum mechanical models of subatomic particles in particle physics and quasiparticles in condensed matter physics.

quantum electrodynamics (QED) : The relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism, giving a complete account of matter and light interaction.

pulley : A wheel on an axle that is designed to support movement of a cable or belt along its circumference; one of six classical simple machines. Pulleys are used in a variety of ways to lift loads, apply forces, and transmit power.

probability : A measure of the expectation that an event will occur or that a statement is true. Probabilities are given a value between 0 (will not occur) and 1 (will occur). The higher the probability of an event, the more certain one can be that the event will occur.

pressure : The ratio of force to the area over which that force is distributed.

pneumatics : The study and control of mechanical force and movement generated by the application of compressed gas.

Planck constant ( h ): Also called Planck’s constant.

A fundamental universal physical constant that is the quantum of action in quantum mechanics.

physical chemistry :The study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of laws and concepts of physics.

photon : An elementary particle, the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force.

periodic table of the elements: Also simply called the periodic table.

A tabular display of the chemical elements organised on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons).

Pascal’s law : A principle in fluid mechanics which states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the initial pressure variations remain the same.

particle physics : A branch of physics that studies the nature of particles, which are the constituents of what is usually referred to as matter and radiation.

parity : 1.  (mathematics)2.  (physics)

optics : The branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light; however, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

optically detected magnetic resonance : An optical technique for the initialisation and readout of quantum spin in some crystal defects.

optical tweezers : An optomechanical device used for the capture, analysis, and manipulation of dielectric objects or particles, which operates via the application of force by the electric field of light.

Ohm’s law : The electric current through a conductor between two points is directly proportional to the potential difference across the two points.

Ohm : The SI derived unit of electrical resistance.

nuclide: Also spelled nucleide.

An atomic species characterized by the specific composition of its nucleus, i.e. by its number of protons, its number of neutrons, and its nuclear energy state.

nanoengineering : The practice of engineering on the nanoscale. Nanoengineering is largely a synonym for nanotechnology, but emphasizes the applied rather the field.

nucleon : Either a proton or a neutron in its role as a component of an atomic nucleus.

nuclear physics : The branch of physics that studies the constituents and interactions of atomic nuclei.

Newton’s laws of motion : A set of three physical laws which describe the relationship between the forces acting on a body and its motion due to those forces. Together they form the basis for classical or Newtonian mechanics.

neutrino : A type of electrically neutral subatomic particle denoted by the Greek letter ν (nu). All evidence suggests that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.

nanotechnology: Also abbreviated as nanotech.

The manipulation of matter on an atomic and molecular scale; a more generalized description by the National Nanotechnology Initiative is “the manipulation of matter with at least one dimension sized from 1 to 100 nanometers”.

muon : An elementary particle, technically classified as a lepton, that is similar to the electron, with unitary negative electric charge (−1) and a spin of 1⁄2. Muons are not believed to have any sub-structure.

motion : Any change in the position of an object over time. Motion can be mathematically described in terms of displacement, distance, velocity, speed, acceleration, and momentum, and is observed by attaching a frame of reference to an observer and measuring the change in an object’s position relative to that frame. An object’s motion cannot change unless it is acted upon by a force.

moment of inertia: A property of a distribution of mass in space that measures its resistance to rotational acceleration about an axis.

molecular physics : A branch of physics that studies the physical properties of molecules and the chemical bonds between atoms as well as their molecular dynamics. It is closely related to atomic physics and overlaps greatly with theoretical chemistry, physical chemistry and chemical physics.

molecule : An electrically neutral group of two or more atoms held together by covalent chemical bonds. Molecules are distinguished from ions by having a net electric charge equal to zero.

molar mass : A physical property of matter defined as the mass of a given substance divided by the amount of substance and expressed in grams per mole.

modulus of elasticity : The mathematical description of an object’s or substance’s tendency to be deformed elastically (i.e. non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region. As such, a stiffer material will have a higher elastic modulus.

meson : A type of hadronic subatomic particle composed of one quark and one antiquark bound together by the strong interaction. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond.

melting: Also called fusion.

A physical process that results in the phase transition of a substance from a solid to a liquid.

mechanics : The branch of science concerned with the behaviour of physical bodies when subjected to forces or displacements and the subsequent effects of the bodies on their environment.

measure of central tendency : A term which relates to the way in which quantitative data tend to cluster around some value. A measure of central tendency is any of a number of ways of specifying this “central value”.

Maxwell’s equations : A set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. Maxwell’s equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.

matter : Any substance (often a particle) that has rest mass and (usually) also volume.

matrix : A rectangular array of numbers, symbols, or expressions arranged in rows and columns. The individual items in a matrix are called its elements or entries.

mathematics : The abstract study of topics encompassing quantity, structure, space, change, and other properties.

mathematical physics : The application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories.

mass number: Also called atomic mass number or nucleon number.

The total number of protons and neutrons (together known as nucleons) in an atomic nucleus.

mass moment of inertia : A property of a distribution of mass in space that measures its resistance to rotational acceleration about an axis.

materials science : An interdisciplinary field incorporating elements of physics, chemistry, and engineering that is concerned with the design and discovery of new materials, particularly solids.

mass flux : The rate of mass flow per unit area. The common symbols are j, J, φ, or Φ, sometimes with subscript m to indicate mass is the flowing quantity. Its SI units are kg s−1 m−2.

mass density : See density.

mass balance: Also called material balance.

An application of the law of conservation of mass to the analysis of physical systems.

magnetism : A property of materials that respond to an applied magnetic field.

magnetic field : A mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field.

Maclaurin series : A representation of a function as an infinite sum of terms that are calculated from the values of the function’s derivatives at a single point.

machine element : An elementary component of a machine. There are three basic types: structural components, mechanisms, and control components.

machine : Any powered tool consisting of one or more parts that is constructed to achieve a particular goal. Machines are usually powered by mechanical, chemical, thermal or electrical means, and are frequently motorised.

Mach number : A dimensionless quantity representing the ratio of the speed of an object moving through a fluid to the local speed of sound.

M-theory : An extension of string theory that attempts to unify seemingly contradictory mathematical formulations and which identifies 11 dimensions.

liquid crystal (LC): A state of matter which has properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way.

liquid : One of four classical states of matter having a definite volume but no fixed shape.

Liouville’s theorem : Phase space volume is conserved.

linear elasticity : The mathematical study of how solid objects deform and become internally stressed due to prescribed loading conditions. Linear elasticity is a simplification of the more general nonlinear theory of elasticity and is a branch of continuum mechanics.

linear algebra : The branch of mathematics concerning vector spaces, often finite or countably infinite dimensional, as well as linear mappings between such spaces.

linear actuator: A form of motor that generates a linear movement directly.

light: A form of electromagnetic radiation that occupies a certain range of wavelengths within the electromagnetic spectrum. In physics, the term sometimes refers collectively to electromagnetic radiation of any wavelength, in which case light includes gamma rays, X-rays, microwaves, and radio waves, but in common usage “light” more often refers specifically to visible light.

lepton : An elementary particle which does not undergo strong interactions but is subject to the Pauli exclusion principle. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons) and neutral leptons (better known as neutrinos).

Laplace–Runge–Lenz vector: Also abbreviated LRL vector.

A vector used chiefly to describe the shape and orientation of the orbit of one astronomical body around another, such as a planet revolving around a star. For two bodies interacting by Newtonian gravity, the LRL vector is a constant of motion, meaning that it is the same no matter where it is calculated on the orbit; equivalently, the LRL vector is said to be conserved.

Kirchhoff’s equationsIn fluid dynamics, a set of equations which describe the motion of a rigid body in an ideal fluid.

laminar flow: Also called streamline flow.

Occurs when a fluid flows in parallel layers with no disruption between the layers.

Kirchhoff’s circuit laws: Also called Kirchhoff’s rules or simply Kirchhoff’s laws.

Two approximate equalities that deal with the current and voltage in electrical circuits. See Kirchhoff’s laws for other meanings of the term.

kinetic energy : The energy that a physical body possesses due to its motion, defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. The body continues to maintain this kinetic energy unless its velocity changes. Contrast potential energy.

kinematics : The branch of classical mechanics that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without consideration of the causes of motion. The study of kinematics is often referred to as the “geometry of motion”.

Kelvin : A scale and unit of measurement of temperature. The Kelvin scale is an absolute thermodynamic temperature scale which uses absolute zero as its null point.

joule : A derived unit of energy, work, or amount of heat in the International System of Units.

isotope : A variant of a particular chemical element. While all isotopes of a given element share the same number of protons, each isotope differs from the others in its number of neutrons.

ionization : The process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions.

ionic bond : A type of chemical bond formed through an electrostatic attraction between two oppositely charged ions.

ion: An atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electric charge.

International System of Units (SI) : The modern form of the metric system, comprising a system of units of measurement devised around seven base units and the convenience of the number ten.

impedance : The measure of the opposition that a circuit presents to a current when a voltage is applied.

ice point : A physical process that results in the phase transition of a substance from a liquid to a solid.

homeokinetics : The physics of complex, self-organizing systems.