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.