## Physical system

In physics, a physical system is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment. The environment is ignored except for its effects on the system. The split between system and envi ...

## Temperature

Temperature is a physical property of matter that quantitatively expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact ...

## Tensor

In mathematics, a tensor is an algebraic object that describes a linear mapping from one set of algebraic objects to another. Objects that tensors may map between include, but are not limited to, vectors and scalars, and, recursively, even other ...

## Ternary fission

Ternary fission is a comparatively rare type of nuclear fission in which three charged products are produced rather than two. As in other nuclear fission processes, other uncharged particles such as multiple neutrons and gamma rays are produced i ...

## Theoretical motivation for general relativity

A theoretical motivation for general relativity, including the motivation for the geodesic equation and the Einstein field equation, can be obtained from special relativity by examining the dynamics of particles in circular orbits about the earth ...

## Thermal conduction

Thermal conduction is the transfer of internal energy by microscopic collisions of particles and movement of electrons within a body. The colliding particles, which include molecules, atoms and electrons, transfer disorganized microscopic kinetic ...

## Thermal conductivity

The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k {\displaystyle k}, λ {\displaystyle \lambda }, or κ {\displaystyle \kappa }. Heat transfer occurs at a lower rate in materials of low ...

## Thermal equilibrium

Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in ther ...

## Thermodynamic limit

The thermodynamic limit, or macroscopic limit, of a system in statistical mechanics is the limit for a large number N of particles where the volume is taken to grow in proportion with the number of particles. The thermodynamic limit is defined as ...

## Thermomass theory

The thermomass theory was proposed by Guo Zengyuan. Recently the thermomass theory has been compared with the extended irreversible thermodynamics and phonon hydrodynamics theory. As a statistic foundation, it has been found that the convective t ...

## Time dilation

Time dilation is a difference in the elapsed time measured by two clocks, either due to them having a velocity relative to each other, or by there being a gravitational potential difference between their locations. After compensating for varying ...

## Tipping point (physics)

Electrical equipment that utilizes heating and cooling systems often incorporate small pop-disc thermostats which open or close at a set temperature that cannot be changed by the end-user. The disc is formed from a bi-metallic sheet, with two lay ...

## Transactional interpretation

The transactional interpretation of quantum mechanics takes the psi and psi* wave functions of the standard quantum formalism to be retarded and advanced waves that form a quantum interaction as a Wheeler–Feynman handshake or transaction. It was ...

## Turbulence

In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between th ...

## Two-body problem

In classical mechanics, the two-body problem is to predict the motion of two massive objects which are abstractly viewed as point particles. The problem assumes that the two objects interact only with one another; the only force affecting each ob ...

## Variable structure system

A variable structure system, or VSS, is a discontinuous nonlinear system of the form x = φ x, t {\displaystyle {\dot {\mathbf {x} }}=\varphi \mathbf {x},t} where x ≜ ^{\operatorname {T} }:\mathbb {R} ^{n+1}\mapsto \mathbb {R} ^{n}} is a piecewise ...

## Vasiliev equations

Vasiliev equations are formally consistent gauge invariant nonlinear equations whose linearization over a specific vacuum solution describes free massless higher-spin fields on anti-de Sitter space. The Vasiliev equations are classical equations ...

## Vector potential

In vector calculus, a vector potential is a vector field whose curl is a given vector field. This is analogous to a scalar potential, which is a scalar field whose gradient is a given vector field. Formally, given a vector field v, a vector poten ...

## Vector space

A vector space is a collection of objects called vectors, which may be added together and multiplied by numbers, called scalars. Scalars are often taken to be real numbers, but there are also vector spaces with scalar multiplication by complex nu ...

## Virial theorem

In mechanics, the virial theorem provides a general equation that relates the average over time of the total kinetic energy of a stable system of discrete particles, bound by potential forces, with that of the total potential energy of the system ...

## Virtual particle

In physics, a virtual particle is a transient quantum fluctuation that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the uncertainty principle. The concept of virtual particles arises in pertu ...

## Viscous stress tensor

The viscous stress tensor is a tensor used in continuum mechanics to model the part of the stress at a point within some material that can be attributed to the strain rate, the rate at which it is deforming around that point. The viscous stress t ...

## Volume (thermodynamics)

In thermodynamics, the volume of a system is an important extensive parameter for describing its thermodynamic state. The specific volume, an intensive property, is the systems volume per unit of mass. Volume is a function of state and is interde ...

## Wave equation

The wave equation is an important second-order linear partial differential equation for the description of waves - as they occur in classical physics - such as mechanical waves or light waves. It arises in fields like acoustics, electromagnetics, ...

## Wave function collapse

In quantum mechanics, wave function collapse occurs when a wave function - initially in a superposition of several eigenstates - reduces to a single eigenstate due to interaction with the external world. This interaction is called an "observation ...

## Wavenumber

In the physical sciences, the wavenumber is the spatial frequency of a wave, measured in cycles per unit distance or radians per unit distance. Whereas temporal frequency can be thought of as the number of waves per unit time, wavenumber is the n ...

## Weak interaction

In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms. Th ...

## Wheelbase

In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels. For road vehicles with more than two axles, the wheelbase is the distance between the steering axle and the centerpoint of the driving ...

## Wigner quasiprobability distribution

The Wigner quasiprobability distribution is a quasiprobability distribution. It was introduced by Eugene Wigner in 1932 to study quantum corrections to classical statistical mechanics. The goal was to link the wavefunction that appears in Schrodi ...

## Wigner–Weyl transform

In quantum mechanics, the Wigner–Weyl transform or Weyl–Wigner transform is the invertible mapping between functions in the quantum phase space formulation and Hilbert space operators in the Schrodinger picture. Often the mapping from functions o ...

## Work function

In solid-state physics, the work function is the minimum thermodynamic work needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" means that the final electron position is far ...

## World tube

In physics, a world tube is the path of an object which occupies a nonzero region of space at every moment in time, as it travels through 4-dimensional spacetime. That is, as it propagates in spacetime, a world tube traces out a three-dimensional ...

## Yang–Mills theory

Yang–Mills theory is a gauge theory based on a special unitary group SU, or more generally any compact, reductive Lie algebra. Yang–Mills theory seeks to describe the behavior of elementary particles using these non-abelian Lie groups and is at t ...

## Assignment (computer science)

In computer programming, an assignment statement sets and/or re-sets the value stored in the storage location denoted by a variable name; in other words, it copies a value into the variable. In most imperative programming languages, the assignmen ...

## Bridging (programming)

In computer science, bridging describes systems that map the runtime behaviour of different programming languages so they can share common resources. They are often used to allow "foreign" languages to operate a host platforms native object libra ...

## Closure (computer programming)

In programming languages, a closure, also lexical closure or function closure, is a technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function togethe ...

## Data type

In computer science and computer programming, a data type or simply type is an attribute of data which tells the compiler or interpreter how the programmer intends to use the data. Most programming languages support basic data types of integer nu ...

## Declaration (computer programming)

In computer programming, a declaration is a language construct that specifies properties of an identifier: it declares what a word "means". Declarations are most commonly used for functions, variables, constants, and classes, but can also be used ...

## Expression (computer science)

An expression in a programming language is a combination of one or more constants, variables, operators, and functions that the programming language interprets and computes to produce another value. This process, as for mathematical expressions, ...

## Identifier (computer science)

An identifier is a name that identifies either a unique object or a unique class of objects, where the "object" or class may be an idea, physical substance. The abbreviation ID often refers to identity, identification, or an identifier. An identi ...

## Identifier (computer programming)

In computer languages, identifiers are tokens which name language entities. Some of the kinds of entities an identifier might denote include variables, types, labels, subroutines, and packages. Which character sequences constitute identifiers dep ...

## Immediately invoked function expression

An immediately invoked function expression is a JavaScript programming language idiom which produces a lexical scope using JavaScripts function scoping. Immediately invoked function expressions can be used to avoid variable hoisting from within b ...

## Label (computer science)

A label in a programming language is a sequence of characters that identifies a location within source code. In most languages labels take the form of an identifier, often followed by a punctuation character. In many high level programming langua ...

## Late binding

Late binding, dynamic binding, or dynamic linkage is a computer programming mechanism in which the method being called upon an object or the function being called with arguments is looked up by name at runtime. With early binding, or static bindi ...

## Name binding

In programming languages, name binding is the association of entities with identifiers. An identifier bound to an object is said to reference that object. Machine languages have no built-in notion of identifiers, but name-object bindings as a ser ...

## Polymorphism (computer science)

In programming languages and type theory, polymorphism is the provision of a single interface to entities of different types or the use of a single symbol to represent multiple different types. The most commonly recognized major classes of polymo ...

## Reference (computer science)

In computer science, a reference is a value that enables a program to indirectly access a particular datum, such as a variables value or a record, in the computers memory or in some other storage device. The reference is said to refer to the datu ...

## Scope (computer science)

In computer programming, the scope of a name binding - an association of a name to an entity, such as a variable - is the region of a computer program where the binding is valid: where the name can be used to refer to the entity. Such a region is ...

## Statement (computer science)

In computer programming, a statement is a syntactic unit of an imperative programming language that expresses some action to be carried out. A program written in such a language is formed by a sequence of one or more statements. A statement may h ...

## Value (computer science)

In computer science, a value is the representation of some entity that can be manipulated by a program. The members of a type are the values of that type. The "value of a variable" is given by the corresponding mapping in the environment. In lang ...