Physics Lournal

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Physical Object

A physical object is commonly defined as a collection of matter, within a defined contiguous boundary, in 3-space.

The boundary must be definable and identifiable via the properties of material, and may change over time.

Usually, the boundary is the tangible surface of the object, and the matter in the object is considered to be constrained to move as one object.

Referenced in

Lagrangian Mechanics

This relates to the concept of a Physical Object, in that the parts of a system which define the shape of a body can be considered to also be defining the boundary of the body, the matter within which is constrained to moving as one object, and because that matter is constrained, there are positions it cannot assume.

A Brief Introduction to Time in Physics

Starting at Classical Mechanics: we index time to the Natural numbers, if we need to treat time as something discrete, or the Real numbers if we need to treat time as something continuous (generally using the latter as it more accurately represents our intuitions about time). Beyond that, there's not a large amount of development of the concept of time, as it is mostly a guidepost, for the path of objects and processes through Space. Time is not where the action is, and thus it's a bit of a background player: time limits, stalls, progresses, or reverses the action.