A mathematical model which seeks to describe atomic nuclei by solving the non-relativistic Schrödinger equation for all constituent nucleons and the forces that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.
In optics and lens design, a measure of a transparent material's dispersion (a variation of refractive index versus wavelength). High values of V indicate low dispersion.
In electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
Any system of measurement 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 possible temperature, understood by international agreement as equivalent to 0 Kelvin or −273.15 °C (−459.67 °F). More formally, it is the theoretical lower limit of the thermodynamic temperature scale, at which enthalpy and entropy of a cooled ideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.
The observation that the expansion of the universe 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. Contrast cohesion.
A process which occurs without transfer of heat or mass of substances between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as work.[5][6] The adiabatic process provides a rigorous conceptual basis for the theory used to expound the first law of thermodynamics, and as such it is a key concept in thermodynamics.
The study of the motion of air, particularly its interaction with a solid object, such as an airplane wing. It is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields.
An optical system that produces no net convergence or divergence of the beam, i.e. has an infinite effective 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's focal length ().
1. In meteorology, a volume of air that is defined by its temperature and water 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. In astronomy, the "amount of air that one is looking through"[8] when observing a star or other celestial source from a vantage point that is within Earth's atmosphere. It is formulated as the integral of air density along the light ray.
Defines the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at the zenith. The air mass coefficient can be used to help characterize the solar spectrum after solar radiation has traveled through the atmosphere.
A type of subatomic particle consisting of two protons and two neutrons bound together into a particle identical to the nucleus of a helium-4ion. It has a charge of +2 e and a mass of 4 u. Alpha particles are classically produced in the process of radioactivealpha decay, but may also be produced in other ways and given the same name.
An electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude 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 its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.[9][10][11]
The change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound, and water waves. The law of reflection says that for specular 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 of angular velocity. In three dimensions, it is a pseudovector. In SI units, it is measured in radians per second squared (rad/s2), and is usually denoted by the Greek letter alpha (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 external torque. For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms inwards, which involves no external torque.
The angle (in radians, degrees, or revolutions) through which a point revolving around a centre or line has been rotated in a specified sense about a specified axis.
Also angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, and pulsatance.
A scalar measure of rotation rate. It refers to the angular displacement per unit time (e.g. in rotation) 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 is angular velocity. The term angular frequency vector is sometimes used as a synonym for the vector quantity angular velocity.[13]
One revolution is equal to 2π radians, hence[13][14]
where:
ω is the angular frequency or angular speed (measured in radians per second),
Also (rarely) moment of momentum or rotational momentum.
The rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity–that is, the total angular momentum of a closed system remains constant.
How fast 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: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital 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. In general, angular velocity is measured in angle per unit time, e.g. radians per second. The SI unit of angular velocity is expressed as radians/sec with the radian having a dimensionless value of unity, thus the SI units of angular velocity are listed as 1/sec. Angular velocity is usually represented by the Greek letter omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
In particle physics, the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons.[15] The total energy and momentum 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 additive quantum 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 as conservation of energy and conservation of momentum are obeyed.[16]
The electrode through which a conventional electric current flows into a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of electron flow, and so electrons flow out of the anode. In a galvanic cell, the anode is the negative terminal or pole which emits electrons toward the external part of an electrical circuit. However, in an electrolytic cell, the anode is the wire or plate having excess positive charge, so named because negatively charged anions tend to move towards it. Contrast cathode.
A theory of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift.
In particle physics, every type of particle has an associated antiparticle with the same mass but with opposite physical charges such as electric charge. For example, the antiparticle of the electron is the antielectron (which is often referred to as the positron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. Some particles, such as the photon, 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-") as antimatter.
It is a subatomic particle of the same mass as a proton but having a negative electric charge and oppositely directed magnetic moment. It is the proton’s antiparticle. Antiprotons were first produced and identified in 1955 by Emilio Segrè, Owen Chamberlain[17]
A physical principle which states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.[18]
The branch of astronomy that deals with the physics of the Universe, especially with the compositional nature of celestial bodies rather than their positions or motions in space.
A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
A periodic vibration whose frequency is in the band audible to the average human, the human hearing range. It is the property of sound that most determines pitch, with a generally accepted standard hearing range for humans is 20 to 20,000 Hz. Also known as audible frequency (AF)
The ratio of the number of constituent particles in a substance, usually atoms or molecules, to the amount of substance, of which the SI unit is the mole. It is defined as exactly 6.02214076×1023 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 hypothetical subatomic particle postulated to account for the rarity of processes that break charge-parity symmetry. It is very light, electrically neutral, and pseudoscalar.
A theorem concerning diffraction 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 structural element that is capable of withstanding load primarily by resisting bending. Beams are traditionally descriptions of building or civil engineering structural 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 reaction induced in a structural element when an external force or moment is applied to the element, causing the element to bend.[20][21] The simplest structural element subjected to bending moments is the beam.
for an arbitrary complex numberα, the order of the Bessel function. Although α and −α produce the same differential equation, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of α. The most important cases are when α is an integer or half-integer. Bessel functions for integer α are also known as cylinder functions or the cylindrical harmonics because they appear in the solution to Laplace's equation in cylindrical coordinates. Spherical Bessel functions with half-integer α are obtained when the Helmholtz equation is solved in spherical coordinates.
The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts.
A hypothetical idealized physical body that completely absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. Perfect black bodies are imagined as substitutes for actual physical bodies in many theoretical discussions of thermodynamics, and the construction of nearly perfect black bodies in the real world remains a topic of interest for materials engineers. Contrast white body.
The type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black 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 the boiling point of a liquid (a solvent) increases when another compound is added, meaning that the resulting solution 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 an ebullioscope.
The angle of incidence at which light with a particular polarization is completely transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected is consequently perfectly polarized.
An Imperial unit of energy defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit; 1 btu is equal to about 1,055 joules. 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 significant plasticdeformation when subjected to stress. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.
The presumably random movement of particles suspended in a fluid (liquid or gas) resulting from their bombardment by fast-moving atoms or molecules in the gas or liquid.
A measure of a substance's resistance to uniform compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.
A branch of mathematics that studies change and has two major sub-fields: differential calculus (concerning rates of change and slopes of curves), and integral 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 the electric charge of a system to the corresponding change in its electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors).
A theoretical ideal thermodynamic cycle proposed by French physicist Nicolas 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 of heat into work, or conversely, the efficiency of a refrigeration 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.
A coordinate system that specifies each point uniquely in a plane by a set of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in the same unit of length. Each reference line is called a coordinate axis or just axis (plural axes) of the system, and the point where they meet is called the origin, at ordered pair (0, 0). The coordinates can also be defined as the positions of the perpendicular projections of the point onto the two axes, expressed as signed distances from the origin.
The electrode through which a conventional electric current flows out of a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of electron flow, and so electrons flow into the cathode. In a galvanic cell, the cathode is the positive terminal or pole which accepts electrons flowing from the external part of an electrical circuit. However, in an electrolytic cell, the cathode is the wire or plate having excess negative charge, so named because positively charged cations tend to move towards it. Contrast anode.
The point in a body around which the resultant torque due to gravity forces vanish. Near the surface of the earth, where gravity acts downward as a parallel force field, the center of gravity and the center of mass are the same.
The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by the inertia of the body as the body's path is continually redirected.
Any attempt in mainstream physics to unify existing theories of relativity, gravitation, and quantum mechanics, particularly by envisioning the three universal constants fundamental to each field – the speed of light (), the gravitational constant (), and the Planck constant () – as the edges of a three-dimensional cube, at each corner of which is positioned a major sub-field within theoretical 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 of chemistry and physics that studies chemical processes from the point of view of physics by investigating physicochemical phenomena using techniques from atomic and molecular physics and condensed matter physics.
A type of light–matter interaction in which a photon is scattered by a charged particle, usually an electron, 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 the Compton effect. The opposite phenomenon occurs in inverse Compton scattering, when a charged particle transfers part of its energy to a photon.
The motion 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 an oscillatory 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 a real 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's velocity and measures how quickly the position of the object changes as time changes. Derivatives are a fundamental tool of calculus.
An electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they would in a conductor 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 is immersed in a fluid, pushing it out of the way and taking its 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 path, typically distinct from the path actually travelled by.
The change in frequency of a wave (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 dry friction, which is nearly independent of velocity, drag forces depend on velocity.
A physical property of matter that causes it to experience a force when near other electrically charged matter. There are two types of electric charge: positive and negative.
The region of space surrounding electrically charged particles and time-varying magnetic 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 a battery or generator and measured in volts. Any device that converts other forms of energy into electrical energy provides electromotive force as its output.
A unit of energy equal to approximately 1.6×10−19joule. By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.
A field that deals with electrical 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 absorbs energy from its surroundings, usually in the form of heat but also in the form of light, electricity, or sound. Contrast exothermic.
The velocity at which the kinetic energy plus the gravitational potential 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 releases energy from a system, usually in the form of heat but also in the form of light, electricity, or sound. Contrast endothermic.
Either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays) and releasing relatively large amounts of energy.
A push or pull. Any interaction that, when unopposed, will change the motion of a physical body. A force has both magnitude and direction, making it a vector quantity. The SI unit used to measure force is the newton.
A model used to explain the influence that a massive body extends into the space around itself, producing a force (gravity) on another massive body. Thus, a gravitational field is used to explain and represent gravitational phenomena. It is measured in newtons per kilogram (N/kg).
The gravitational potential at a location is equal to the work (energy transferred) per unit mass that is done by the force of gravity to move an object to a fixed reference location.
A ripple in the curvature of spacetime that propagates as a wave 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 of radioactive 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 isotopes of a given element share the same number of protons, each isotope differs from the others in its number of neutrons.
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".
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.
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.
A device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation"
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).
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.
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.
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 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.
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, particularly solids.
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.
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.
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.
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 to forces or displacements and the subsequent effects of the bodies on their environment.
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.
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.
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.
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.
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.
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 nanometres".
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.
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.
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.
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.
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.
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.
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).
The natural science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe 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.
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.
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 at 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.
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.
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.
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.
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.
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.
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).
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.
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).
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.
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.
A mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas and composed of frequencies within the range of human hearing.
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 vacuum, as opposed to the speed of light through some physical medium.
Any nuclide that is not radioactive and does not spontaneously undergo radioactive decay, as opposed to a radionuclide. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.
The branch of mechanics concerned with the analysis of loads (force and torque, 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 constant velocity.
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 an endothermic phase transition that occurs at temperatures and pressures below a substance's triple point in its phase diagram.
A phenomenon of exactly zero electrical resistance and expulsion of magnetic 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 to experimental physics, which relies on data generated by experimental observations.
A state in which there is no net flow of thermal 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 the temperature within the system is spatially and temporally uniform. Systems in thermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true.
The tendency of a force 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 absorb energy and plastically deform 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 when stressed.
Any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, such as position x and momentum p, cannot be known simultaneously.
A mathematical structure formed by a collection of elements called vectors, which may be added together and multiplied ("scaled") by numbers called scalars.
A vector quantity defined as the rate of change of the position of an object with respect to a given frame of reference. Velocity specifies both an object's speed and direction of motion (e.g. 60 kilometres per hour to the north).
An instrument used for measuring the difference in electric potential between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit.
A derived unit of power 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 classical simple machines.
white body
A hypothetical idealized physical body that reflects all incident electromagnetic radiation completely and uniformly in all directions; the opposite of a black body.
A high-energy photon (between 100 eV and 100 keV) with a wavelength shorter than that of ultraviolet radiation and longer than that of gamma radiation.
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)
