in: classical physics, particularly mechanics
is: an object that can be treated as occupying a single point in space, at any time. [P2.1, P2.2, P2.4]
is thought of: as having no size, shape or internal motion (such as spin or vibration). [P2.1, P2.2, P2.4]
is emulated: by the centre of mass of an extended object. [P2.1, P2.2]
is: the simplest possible example of a (classical) physical system.
more generally, is: (especially in quantum physics) a fundamental constituent of matter, such as an elementary particle or (exceptionally) an atom or molecule.
See also quantum.
Copyright 1997, The Open University