In natural language and physical science, a physical object or material object (or simply an object or body) is a contiguous collection of matter, within a defined boundary (or surface), that exists in

space Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions. Modern physicists usually consider it, with time, to be part of a boundless ...

and

time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...

. Usually contrasted with abstract objects and mental objects. Also in common usage, an object is not constrained to consist of the same collection of matter. Atoms or parts of an object may change over time. An object is usually meant to be defined by the simplest representation of the boundary consistent with the observations. However the laws of physics only apply directly to objects that consist of the same collection of matter. In

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, an object is an identifiable collection of matter, which may be constrained by an identifiable boundary, and may move as a unit by translation or rotation, in 3-dimensional space. Each object has a unique identity, independent of any other properties. Two objects may be identical, in all properties except position, but still remain distinguishable. In most cases the boundaries of two objects may not overlap at any point in time. The property of identity allows objects to be counted. Examples of models of physical bodies include, but are not limited to a particle, several interacting smaller bodies ( particulate or otherwise). Discrete objects are in contrast to continuous media. The common conception of physical objects includes that they have extension in the physical world, although there do exist theories of quantum physics and cosmology which arguably challenge this. In modern physics, "extension" is understood in terms of the spacetime: roughly speaking, it means that for a given moment of

the body has some location in the space (although not necessarily amounting to the abstraction of a point in space and time). A physical body as a whole is assumed to have such quantitative properties as mass, momentum,

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

, other conserved quantities, and possibly other quantities. An object with known composition and described in an adequate physical theory is an example of

physical system A physical system is a collection of physical objects under study. The collection differs from a set: all the objects must coexist and have some physical relationship. In other words, it is a portion of the physical universe chosen for analys ...

In common usage

An object is known by the application of

sense A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of Stimulus (physiology), stimuli. Although, in some cultures, five human senses were traditio ...

s. The properties of an object are inferred by learning and reasoning based on the information perceived. Abstractly, an object is a construction of our mind consistent with the information provided by our senses, using Occam's razor. In common usage an object is the material inside the boundary of an object, in three-dimensional space. The boundary of an object is a contiguous surface which may be used to determine what is inside, and what is outside an object. An object is a single piece of material, whose extent is determined by a description based on the properties of the material. An imaginary sphere of granite within a larger block of granite would not be considered an identifiable object, in common usage. A fossilized skull encased in a rock may be considered an object because it is possible to determine the extent of the skull based on the properties of the material. For a rigid body, the boundary of an object may change over time by continuous translation and

rotation Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...

. For a deformable body the boundary may also be continuously deformed over time in other ways. An object has an identity. In general two objects with identical properties, other than position at an instance in time, may be distinguished as two objects and may not occupy the same space at the same time (excluding component objects). An object's identity may be tracked using the continuity of the change in its boundary over time. The identity of objects allows objects to be arranged in sets and counted. The material in an object may change over time. For example, a rock may wear away or have pieces broken off it. The object will be regarded as the same object after the addition or removal of material, if the system may be more simply described with the continued existence of the object, than in any other way. The addition or removal of material may discontinuously change the boundary of the object. The continuation of the object's identity is then based on the description of the system by continued identity being simpler than without continued identity. For example, a particular car might have all its wheels changed and still be regarded as the same car. The identity of an object may not split. If an object is broken into two pieces at most one of the pieces has the same identity. An object's identity may also be destroyed if the simplest description of the system at a point in time changes from identifying the object to not identifying it. Also an object's identity is created at the first point in time that the simplest model of the system consistent with perception identifies it. An object may be composed of components. A component is an object completely within the boundary of a containing object. A living thing may be an object, and is distinguished from non-living things by the designation of the latter as ''inanimate objects''. Inanimate objects generally lack the capacity or desire to undertake actions, although humans in some cultures may tend to attribute such characteristics to non-living things.

In physics

Classical mechanics

classical mechanics Classical mechanics is a Theoretical physics, physical theory describing the motion of objects such as projectiles, parts of Machine (mechanical), machinery, spacecraft, planets, stars, and galaxies. The development of classical mechanics inv ...

a physical body is a collection of matter having properties including mass,

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

, momentum and

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

. The matter exists in a volume of three-dimensional space. This space is its extension. Interactions between objects are partly described by orientation and external shape. In

continuum mechanics Continuum mechanics is a branch of mechanics that deals with the deformation of and transmission of forces through materials modeled as a ''continuous medium'' (also called a ''continuum'') rather than as discrete particles. Continuum mec ...

an object may be described as a collection of sub-objects, down to an infinitesimal division, which interact with each other by forces that may be described internally by

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

and mechanical stress.

Quantum mechanics

quantum mechanics Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

an object is a particle or collection of particles. Until measured, a particle does not have a physical position. A particle is defined by a probability distribution of finding the particle at a particular position. There is a limit to the accuracy with which the position and velocity may be measured. A particle or collection of particles is described by a

quantum state In quantum physics, a quantum state is a mathematical entity that embodies the knowledge of a quantum system. Quantum mechanics specifies the construction, evolution, and measurement of a quantum state. The result is a prediction for the system ...

. These ideas vary from the common usage understanding of what an object is.

String theory

particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

, there is a debate as to whether some elementary particles are not bodies, but are points without extension in physical space within spacetime, or are always extended in at least one dimension of space as in string theory or M theory.

In psychology

In some branches of

psychology Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...

, depending on school of thought, a physical object has physical properties, as compared to mental objects. In ( reductionistic) behaviorism, objects and their properties are the (only) meaningful objects of study. While in modern-day behavioral psychotherapy, it is still only the means for goal-oriented behavior modifications, in Body Psychotherapy it is not a means only anymore, but its felt sense is a goal of its own. In cognitive psychology, physical bodies as they occur in

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

are studied in order to understand the

mind The mind is that which thinks, feels, perceives, imagines, remembers, and wills. It covers the totality of mental phenomena, including both conscious processes, through which an individual is aware of external and internal circumstances ...

, which may not be a physical body, as in functionalist schools of thought.

In philosophy

A physical body is an enduring object that exists throughout a particular trajectory of

and orientation over a particular duration of

, and which is located in the

world The world is the totality of entities, the whole of reality, or everything that Existence, exists. The nature of the world has been conceptualized differently in different fields. Some conceptions see the world as unique, while others talk ...

of physical space (i.e., as studied by

). This contrasts with

abstract object In philosophy and the arts, a fundamental distinction exists between abstract and concrete entities. While there is no universally accepted definition, common examples illustrate the difference: numbers, sets, and ideas are typically classif ...

s such as mathematical objects which do not exist at any particular time or place. Examples are a cloud, a human body, a banana, a billiard ball, a table, or a proton. This is contrasted with abstract objects such as mental objects, which exist in the mental world, and mathematical objects. Other examples that are ''not'' physical bodies are emotions, the concept of "

justice In its broadest sense, justice is the idea that individuals should be treated fairly. According to the ''Stanford Encyclopedia of Philosophy'', the most plausible candidate for a core definition comes from the ''Institutes (Justinian), Inst ...

", a feeling of hatred, or the number "3". In some philosophies, like the

idealism Idealism in philosophy, also known as philosophical realism or metaphysical idealism, is the set of metaphysics, metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, Spirit (vital essence), spirit, or ...

of George Berkeley, a physical body ''is'' a mental object, but still has extension in the space of a visual field.

References

External links

* {{Authority control Concepts in metaphysics Concepts in physics Mechanics Ontology