Also in common usage, an object is not constrained to consist of the same collection ofmatter. 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.
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.
The common conception of physical objects includes that they haveextension in thephysical world, although there do existtheories ofquantum physics andcosmology which arguably challenge[how?] this. In modern physics, "extension" is understood in terms of thespacetime: roughly speaking, it means that for a given moment oftime the body has some location in the space (although not necessarily amounting to the abstraction of apoint inspace and time). A physical body as a whole is assumed to have suchquantitative properties asmass,momentum,electric charge, otherconserved quantities, and possibly other quantities.
An object with known composition and described in an adequate physical theory is an example ofphysical system.
An object is known by the application ofsenses. 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, usingOccam'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.
An object has anidentity. 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 insets andcounted.
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 asinanimate 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.[3]
Interactions between objects are partly described by orientation and external shape.
Incontinuum mechanics 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 bypressure andmechanical stress.
A physical body is an enduring object that exists throughout a particulartrajectory ofspace and orientation over a particular duration oftime, and which is located in theworld ofphysical space (i.e., as studied byphysics). This contrasts withabstract objects such asmathematical objects which do not exist at any particular time or place.
^Oxford English Dictionary, "Physical object (n.),” September 2024. "Philosophy. Originally: a concrete object that exists in space and time, esp. one perceivable through the senses. Now also: any spatio-temporal object; any object amenable to study by the physical sciences. Often contrasted with objects that are abstract (propositions, numbers, etc.) or mental (ideas, intentions, etc.)."
^Oxford English Dictionary, “Material object (n.),” September 2024. "A thing made or consisting of matter, a physical object; (Philosophy) an object having a real physical existence independent of mind or consciousness."
