A mathematical model which seeks to describeatomic nuclei by solving the non-relativisticSchrödinger equation for all constituentnucleons and theforces that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.
Inelectrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
Any system ofmeasurement that begins at a minimum, or zero point, and progresses in only one direction. The zero point of an absolute scale is a natural minimum, leaving only one direction in which to progress, whereas an arbitrary or "relative" scale begins at some point selected by a person and can progress in both directions.
The theoretical lowest possibletemperature, understood by international agreement as equivalent to 0Kelvin or −273.15 °C (−459.67 °F). More formally, it is the theoretical lower limit of thethermodynamic temperature scale, at whichenthalpy andentropy of a cooledideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.
The observation that theexpansion of theuniverse is such that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.[1][2][3][4]
adhesion is what makes things stick together.It's the force that allows tape to stick to a surface or glue to hold two objects together. Contrastcohesion.
A process which occurs without transfer ofheat ormass of substances between athermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only aswork.[5][6] The adiabatic process provides a rigorous conceptual basis for the theory used to expound thefirst law of thermodynamics, and as such it is a key concept inthermodynamics.
The study of the motion ofair, particularly its interaction with a solid object, such as anairplane wing. It is a sub-field offluid dynamics andgas dynamics, and many aspects of aerodynamics theory are common to these fields.
aerophysics
the study of air and the design, construction, and operation of devices that move rapidly through the air, such as aircraft, missiles and rockets.
Anoptical system that produces no net convergence or divergence of the beam, i.e. has an infiniteeffective focal length.[7] This type of system can be created with a pair of optical elements where the distance between the elements is equal to the sum of each element'sfocal length ().
1. Inmeteorology, a volume ofair that is defined by itstemperature andwater vapor content. Air masses may cover many hundreds or thousands of square miles and generally adapt to the characteristics of the surface below them. They are often classified according to their latitude and their source regions.
2. Inastronomy, the "amount of air that one is looking through"[8] when observing a star or other celestial source from a vantage point that is withinEarth's atmosphere. It is formulated as the integral of air density along the lightray.
Defines the direct optical path length through theEarth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at thezenith. The air mass coefficient can be used to help characterize the solar spectrum aftersolar radiation has traveled through the atmosphere.
A type ofsubatomic particle consisting of twoprotons and twoneutrons bound together into a particle identical to thenucleus of ahelium-4ion. It has a charge of+2 e and a mass of4 u. Alpha particles are classically produced in the process ofradioactivealpha decay, but may also be produced in other ways and given the same name.
An electronic device that can increase thepower of asignal (a time-varyingvoltage orcurrent). It is atwo-port electronic circuit that uses electric power from apower supply to increase theamplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by itsgain: the ratio of output voltage, current, or power to input. By definition, an amplifier is any circuit that has apower gain greater than one.[9][10][11]
The change in direction of awavefront at aninterface between two differentmedia such that the wavefront returns into the medium from which it originated. Common examples include the reflection oflight,sound, andwater waves. Thelaw of reflection says that forspecular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected.Mirrors exhibit specular reflection.
The time rate of change ofangular velocity. In three dimensions, it is apseudovector. InSI units, it is measured inradians per second squared (rad/s2), and is usually denoted by the Greek letteralpha (α).[12] Just like angular velocity, there are two types of angular acceleration: spin angular acceleration and orbital angular acceleration, representing the time rate of change of spin angular velocity and orbital angular velocity, respectively. Unlike linear acceleration, angular acceleration need not be caused by a net externaltorque. For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms inwards, which involves noexternal torque.
The angle (inradians,degrees, orrevolutions) through which a point revolving around a centre or line has been rotated in a specified sense about a specifiedaxis.
A scalar measure of rotation rate. It refers to theangular displacement per unit time (e.g. in the rotation of an astronomical body) or the rate of change of the phase of a sinusoidal waveform (e.g. in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the vector quantity that isangular velocity. The termangular frequency vector is sometimes used as a synonym for the vector quantity angular velocity.[13]Onerevolution is equal to 2πradians, hence[13][14]
where:
ω is the angular frequency or angular speed (measured inradians per second),
Also (rarely)moment of momentum orrotational momentum.
The rotational equivalent oflinear momentum. It is an important quantity in physics because it is aconserved quantity–that is, the total angular momentum of aclosed system remains constant.
A measure of the rate at which an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity:spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation, whereasorbital angular velocity refers to how fast a rigid body's centre of rotation revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. Angular velocity is generally expressed as an angle or arc per unit time; e.g. theSI unit of angular velocity isradians per second (rad/sec), with the radian having a dimensionless value of unity, so that the unit is often written as1/sec. Angular velocity is usually represented by the Greek letteromega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
Inparticle physics, the process that occurs when asubatomic particle collides with its respectiveantiparticle to produce other particles, such as anelectron colliding with apositron to produce twophotons.[15] The totalenergy andmomentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additivequantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence any set of particles may be produced whose total quantum numbers are also zero as long asconservation of energy andconservation of momentum are obeyed.[16]
The electrode through which a conventionalelectric current flows into apolarized electrical device; the direction of current flow is, by convention, opposite to the direction ofelectron flow, and so electrons flowout of the anode. In agalvanic cell, the anode is the negative terminal or pole which emits electrons toward the external part of anelectrical circuit. However, in anelectrolytic cell, the anode is the wire or plate having excesspositive charge, so named because negatively chargedanions tend to move towards it. Contrastcathode.
A theory of creating a place or object that is free from the force ofgravity. It does not refer to the lack of weight under gravity experienced infree fall ororbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift.
Inparticle physics, every type ofparticle has an associated antiparticle with the samemass but with oppositephysical charges such aselectric charge. For example, the antiparticle of theelectron is theantielectron (often referred to as thepositron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types ofradioactive decay. Some particles, such as thephoton, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as "normal" matter (the kind comprising all matter with which humans usually interact), and the other (usually given the prefix "anti-") asantimatter.
A physical principle which states that the upwardbuoyant force that is exerted on a body immersed in afluid, whether fully or partially submerged, is equal to theweight of the fluid that the bodydisplaces and acts in the upward direction at the center of mass of the displaced fluid.[18]
The branch ofastronomy that deals with the physics of theUniverse, especially with the compositional nature of celestial bodies rather than their positions or motions in space.
A basic unit ofmatter that consists of a dense centralnucleus surrounded by a cloud of negatively chargedelectrons. The atomic nucleus contains a mix of positively chargedprotons and electrically neutralneutrons.
A periodic vibration whose frequency is in the band audible to the average human, i.e. within the standard human hearing range (generally accepted as 20 to 20,000 Hz). It is the property of sound that most determines pitch.
The ratio of the number of constituentparticles in a substance, usuallyatoms ormolecules, to theamount of substance, of which theSI unit is the mole. It is defined as exactly6.02214076×1023 mol−1.
A physical law which states that volumes of gases which are equal to each other at the same temperature and pressure will contain equal numbers of molecules.
A hypotheticalsubatomic particle postulated to account for the rarity of processes that break charge-parity symmetry. It is very light, electrically neutral, and pseudoscalar.
A theorem concerningdiffraction which states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
A class of compositesubatomic particle in thehadron family, such as aproton or aneutron, each of which is made of (usually) threequarks. Nearly allmatter humans are likely to encounter is baryonic matter. Baryons are also consideredfermions.
A structural element that is capable of withstanding a load primarily by resisting bending. Beams are traditionally descriptions of building or civil engineeringstructural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
The behavior of a slender structural element (e.g. abeam) which is subjected to an external load applied perpendicularly to a longitudinal axis of the element.
The reaction induced in astructural element when an externalforce ormoment is applied to the element, causing the element tobend.[20][21] The simplest structural element subjected to bending moments is thebeam.
The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lowerpotential energy than the sum of its constituent parts.
A hypothetical idealized physical body that completely absorbs all incidentelectromagnetic radiation, regardless offrequency orangle of incidence. Perfect black bodies are imagined as substitutes for actual physical bodies in many theoretical discussions ofthermodynamics, and the construction of nearly perfect black bodies in the real world remains a topic of interest for materials engineers. Contrastwhite body.
The type ofelectromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by ablack body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
The phenomenon by which theboiling point of aliquid (asolvent) increases when another compound is added, meaning that the resultingsolution has a higher boiling point than the pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. The boiling point can be measured accurately using anebullioscope.
The angle of incidence at whichlight with a particularpolarization is completely transmitted through a transparentdielectric surface, with noreflection. When unpolarized light is incident at this angle, the light that is reflected is consequently perfectly polarized.
An Imperial unit ofenergy defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit; 1 btu is equal to about 1,055joules. In scientific contexts the btu has largely been replaced by the SI unit of energy, the joule.
The tendency of a material to break without significantplasticdeformation when subjected tostress. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.
The apparently random movement of particles suspended in a fluid (liquid or gas) resulting from their continuous bombardment by fast-movingatoms or molecules in the gas or liquid.
A globule of a gaseous substance immersed or suspended in a liquid; e.g. a pocket of air completely enclosed by water, usually but not necessarily assuming a spherical shape.
A measure of a substance's resistance to uniformcompression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is thepascal.
A branch ofmathematics that studies change and has two major sub-fields:differential calculus (concerning rates of change and slopes of curves), andintegral calculus (concerning accumulation of quantities and the areas under and between curves). These two branches are related to each other by the fundamental theorem of calculus.
The ratio of the change in theelectric charge of a system to the corresponding change in itselectric potential. There are two closely related notions of capacitance:self capacitance andmutual capacitance. Any object that can be electrically charged exhibitsself capacitance. A material with a large self capacitance holds more electric charge at a givenvoltage than one with low capacitance. The notion ofmutual capacitance is particularly important for understanding the operations of thecapacitor, one of the three elementarylinear electronic components (along withresistors andinductors).
A theoretical idealthermodynamic cycle proposed by French physicistNicolas Léonard Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. It provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion ofheat intowork, or conversely, the efficiency of arefrigeration system in creating a temperature difference by the application of work to the system. It is not an actual thermodynamic cycle but is a theoretical construct.
Acoordinate system that specifies eachpoint uniquely in aplane by a set ofnumerical coordinates, which are thesigned distances to the point from two fixedperpendicular oriented lines, measured in the sameunit of length. Each reference line is called acoordinate axis or justaxis (pluralaxes) of the system, and the point where they meet is called theorigin, at ordered pair(0, 0). The coordinates can also be defined as the positions of theperpendicular projections of the point onto the two axes, expressed as signed distances from the origin.
The electrode through which a conventionalelectric current flows out of a polarized electrical device; the direction of current flow is, by convention, opposite to the direction ofelectron flow, and so electrons flowinto the cathode. In agalvanic cell, the cathode is the positive terminal or pole which accepts electrons flowing from the external part of anelectrical circuit. However, in anelectrolytic cell, the cathode is the wire or plate having excessnegative charge, so named because positively chargedcations tend to move towards it. Contrastanode.
The point in a body around which the resultanttorque due togravity forces vanish. Near the surface of the earth, where gravity acts downward as a parallel force field, the center of gravity and thecenter of mass are the same.
The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by theinertia of the body as the body's path is continually redirected.
Any attempt in mainstream physics tounify existing theories ofrelativity,gravitation, andquantum mechanics, particularly by envisioning the three universal constants fundamental to each field – thespeed of light (), thegravitational constant (), and thePlanck constant () – as the edges of a three-dimensional cube, at each corner of which is positioned a major sub-field withintheoretical physics according to which of the three constants are accounted for by that sub-field and which are ignored. One corner of this so-called "cube of theoretical physics", where all three constants are accounted for simultaneously, has not yet been satisfactorily described:quantum gravity.
A branch ofchemistry and physics that studies chemical processes from the point of view of physics by investigating physicochemical phenomena using techniques from atomic and molecular physics andcondensed matter physics.
A type of light–matter interaction in which aphoton is scattered by acharged particle, usually anelectron, which results in part of the energy of the photon being transferred to the recoiling electron; a resulting decrease in the energy of the photon is called theCompton effect. The opposite phenomenon occurs ininverse Compton scattering, when a charged particle transfers part of its energy to a photon.
Themotion of a moving particle or object that conforms to a known or fixed curve. Such motion is studied with two coordinate systems: planar motion and cylindrical motion.
Any influence upon or within anoscillatory system that has the effect of reducing, restricting, or preventing its oscillations. Damping is a result of processes that dissipate the energy stored in the oscillation.
For a mathematical function of areal variable, a measurement of the sensitivity to change of the function value (output) with respect to a change in its argument (input); e.g. the derivative of the position of a moving object with respect to time is the object'svelocity and measures how quickly the position of the object changes as time changes. Derivatives are a fundamental tool ofcalculus.
An electricalinsulator that can bepolarized by an appliedelectric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they would in aconductor but only shift slightly from their equilibrium positions, with positive charges displaced in the direction of the field's flow and negative charges displaced in the opposite direction; this creates an internal electric field that reduces the larger field within the dielectric material.
1. (fluid) Occurs when an object or substance is immersed in a fluid, pushing the fluid particles out of the way and taking their place. The volume of the immersed object will be exactly equal to the volume of the displaced fluid, so that the volume of the immersed object can be deduced if the volume of the displaced fluid is measured.
2. (vector) The shortest distance from the initial to the final position of a point. Thus, it is the length of an imaginary straight-line path, typically distinct from the path actually travelled.
The change infrequency of awave (or other periodic event) for an observer moving relative to its source. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.
Forces which act on a solid object in the direction of the relative fluid flow velocity. Unlike other resistive forces, such as dryfriction, which is nearly independent of velocity, drag forces depend on velocity.
A physical property ofmatter that causes it to experience aforce when near other electrically charged matter. There are two types of electric charge: positive and negative.
The region of space surrounding electricallycharged particles and time-varyingmagnetic fields. The electric field represents the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
The electrical intensity or "pressure" developed by a source of electrical energy such as abattery orgenerator and measured involts. Any device that converts other forms ofenergy into electrical energy provides electromotive force as its output.
A unit ofenergy equal to approximately 1.6×10−19joule. By definition, it is the amount of energy gained by the charge of a singleelectron moved across an electric potential difference of onevolt.
A field that deals withelectrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, and integrated circuits as well as associated passive interconnection technologies.
An adjective used to refer to a process or reaction in which a system absorbsenergy from its surroundings, usually in the form ofheat but also in the form oflight,electricity, orsound. Contrastexothermic.
Thevelocity at which thekinetic energy plus the gravitationalpotential energy of an object is zero. It is the speed needed to "escape" from a gravitational field without further propulsion.
An adjective used to refer to a process or reaction that releasesenergy from a system, usually in the form ofheat but also in the form oflight,electricity, orsound. Contrastendothermic.
Either a nuclear reaction or aradioactive decay process in which thenucleus of an atom splits into smaller parts (lighter nuclei), often producing freeneutrons andphotons (in the form ofgamma rays) and releasing relatively large amounts of energy.
Any interaction or influence that, unless counterbalanced by other forces, will cause a physical body to change itsvelocity or shape. A force has both magnitude and direction, making it avector quantity. TheSI unit used to measure force is thenewton.
A model used to explain the influence that a massive body extends into the space around itself, producing aforce (gravity) capable of interacting with or influencing other nearby physical bodies. Thus, a gravitational field is used to explain and represent gravitational phenomena. It is measured innewtons per kilogram (N/kg).
The gravitational potential at a location is equal to thework (energy transferred) per unitmass that is done by the force ofgravity to move an object to a fixed reference location.
A ripple in the curvature ofspacetime that propagates as awave and is generated in certain gravitational interactions, travelling outward from their source.
The time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, half-life typically refers to a property ofradioactive decay, but may refer to any quantity which follows an exponential decay.
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.
A variant of a particular chemical element. While all atoms of a given element share the same number ofprotons, each isotope differs from the others in its number ofneutrons.
The branch ofclassical mechanics that describes themotion 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".
Theenergy that a physical body possesses due to itsmotion, defined as thework needed toaccelerate a body of a givenmass from rest to its statedvelocity. The body continues to maintain this kinetic energy unless its velocity changes. Contrastpotential energy.
Avector 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.
A device that emitslight through a process of optical amplification based on the stimulated emission ofelectromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation".
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 generalnonlinear theory of elasticity and is a branch ofcontinuum mechanics.
Astate 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 itsmolecules may be oriented in a crystal-like way.
The proposition that the existence of absolute rotation (the distinction of local inertial frames vs. rotating reference frames) is determined by the large-scale distribution of matter.
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.
A mathematical description of themagnetic influence ofelectric 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 avector field.
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.
An interdisciplinary field incorporating elements of physics, chemistry, and engineering that is concerned with the design and discovery of new materials, particularlysolids.
The application ofmathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories.
A rectangular array of numbers, symbols, or expressions arranged in rows and columns. The individual items in a matrix are called itselements orentries.
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 howelectric andmagnetic fields are generated and altered by each other and bycharges andcurrents.
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".
The branch of science concerned with the behaviour of physical bodies when subjected toforces or displacements and the subsequent effects of the bodies on their environment.
The mathematical description of an object's or substance's tendency to bedeformed elastically (i.e. non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of itsstress–strain curve in the elastic deformation region. As such, astiffer material will have a higher elastic modulus.
An electrically neutral group of two or moreatoms held together by covalent chemical bonds. Molecules are distinguished fromions by having a netelectric charge equal to zero.
A branch of physics that studies the physical properties ofmolecules and the chemical bonds betweenatoms as well as their molecular dynamics. It is closely related to atomic physics and overlaps greatly with theoretical chemistry,physical chemistry andchemical physics.
Any change in the position of an object overtime. Motion can be mathematically described in terms ofdisplacement,distance,velocity,speed,acceleration, andmomentum, and is observed by attaching aframe 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 aforce.
Anelementary particle, technically classified as alepton, that is similar to theelectron, with unitary negative electric charge (−1) and a spin of 1⁄2. Muons are not believed to have any sub-structure.
The manipulation of matter on anatomic andmolecular scale; a more generalized description by theNational Nanotechnology Initiative is "the manipulation of matter with at least one dimension sized from 1 to 100 nanometres".
A type of electrically neutralsubatomic particle denoted by the Greek letter ν (nu). All evidence suggests that neutrinos havemass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.
A set of three physical laws which describe the relationship between theforces acting on a body and its motion due to those forces. Together they form the basis forclassical or Newtonian mechanics.
Anoptomechanical device used for the capture, analysis, and manipulation ofdielectric objects or particles, which operates via the application offorce by theelectric field of light.
The branch of physics which involves the behaviour and properties oflight, 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 ofelectromagnetic radiation such asX-rays, microwaves, and radio waves exhibit similar properties.
A principle influid mechanics which states thatpressure 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.
A tabular display of thechemical elements organised on the basis of theiratomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons).
The natural science that involves the study ofmatter and its motion throughspace andtime, along with related concepts such asenergy andforce. More broadly, it is the general analysis ofnature, conducted in order to understand how theuniverse behaves.
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.
Awheel on an axle that is designed to support movement of a cable or belt along its circumference; one of six classicalsimple machines. Pulleys are used in a variety of ways to lift loads, applyforces, and transmitpower.
A branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of thePlanck constant. Quantum mechanics departs fromclassical mechanics atatomic andsubatomic 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.
An elementaryparticle and a fundamental constituent ofmatter. Quarks combine to form composite particles calledhadrons, the most stable of which areprotons andneutrons, the components ofatomic nuclei.
Anynuclide possessing excess nuclearenergy to the point that it is unstable. Such excess energy is emitted through any of several processes ofradioactive decay, resulting in astable nuclide or sometimes another unstable radionuclide which can then undergo further decay. Certain radionuclides occur naturally; many others can be produced artificially innuclear reactors,cyclotrons,particle accelerators, or radionuclide generators.
A phenomenon which occurs whenlight seen coming from an object that is moving away from the observer is proportionally increased inwavelength or "shifted" to thered end of thevisible light spectrum.
The change in direction of awave as it passes from onetransmission medium to another or as a result of a gradual change in the medium. Though most commonly used in the context of refraction oflight, other waves such assound waves andfluid waves also experience refraction.
An idealization of a solid body in whichdeformation is neglected. In other words, thedistance 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 torelativity, objects can normally be assumed to be perfectly rigid if they are not moving near thespeed of light.
Any simple physical quantity that can be described by a single number (as opposed tovectors,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).
The general physical process by which some forms ofradiation, such aslight,sound, or moving particles, are forced to deviate from a straighttrajectory by one or more localised non-uniformities in the medium through which they pass.
A mechanical device that changes the direction or magnitude of aforce. 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).
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 ofgravity. The term may also more generally refer to a wide variety of devices involving the flow of liquids through tubes.
The tendency of asolid,liquid, orgaseous chemical substance (called asolute) to dissolve in another solid, liquid, or gaseous substance (called asolvent) 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 ontemperature andpressure.
A mechanicalwave that is an oscillation ofpressure transmitted through a solid, liquid, or gas and composed of frequencies within the range of human hearing.
A fundamental universalphysical 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 oflight invacuum, as opposed to the speed of light through some physical medium.
Anynuclide that is not radioactive and does not spontaneously undergoradioactive decay, as opposed to aradionuclide. When such nuclides are referred to in relation to specific elements, they are usually termedstable isotopes.
The branch of mechanics concerned with the analysis of loads (force andtorque, or "moment") on physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at a constantvelocity.
The transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body.
The physical process by which matter is transformed directly from the solid phase to the gas phase without passing through an intermediate liquid phase. Sublimation is anendothermic phase transition that occurs at temperatures and pressures below a substance'striple point in its phase diagram.
A phenomenon of exactly zeroelectrical resistance and expulsion ofmagnetic fields occurring in certain materials when cooled below a characteristic critical temperature.
A branch of physics that employs mathematical models and abstractions of physical objects and systems in order to rationalize, explain, and predict natural phenomena, as opposed toexperimental physics, which relies on data generated by experimental observations.
A state in which there is no net flow ofthermal energy between two physical systems when the systems are connected by a path permeable to heat. A system may also be said to be in thermal equilibrium with itself if thetemperature within the system is spatially and temporally uniform. Systems inthermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true.
The tendency of aforce to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object.
The ability of a material to absorbenergy and plasticallydeform without fracturing. Material toughness is defined as the amount of energy per unit volume that a material can absorb before rupturing. It is also defined as the resistance to fracture of a material whenstressed.
Any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of aparticle, such as positionx and momentump, cannot be known simultaneously.
A mathematical structure formed by a collection of elements calledvectors, which may be added together and multiplied ("scaled") by numbers calledscalars.
Avector quantity defined as therate of change of the position of an object with respect to a givenframe of reference. Velocity specifies both an object'sspeed and direction ofmotion (e.g. 60 kilometres per hour to the north).
An instrument used for measuring the difference inelectric potential between two points in anelectric circuit. Analog voltmeters move a pointer across a scale in proportion to thevoltage of the circuit.
A derived unit ofpower in the International System of Units (SI) defined as one joule per second. The watt measures the rate of energy conversion or transfer.
A wheel attached to an axle in such a way that the two parts rotate together and transfer forces between them; one of six classicalsimple machines.
white body
A hypothetical idealized physical body that reflects all incidentelectromagnetic radiation completely and uniformly in all directions; the opposite of ablack body.
The effect of splitting a spectral line into several components in the presence of a static magnetic field by the lifting of degeneracy in electronic states.
^abCummings, Karen; Halliday, David (2007).Understanding physics. New Delhi: John Wiley & Sons Inc., authorized reprint to Wiley - India. pp. 449, 484, 485, 487.ISBN978-81-265-0882-2.(UP1)
