Editing Point particle (section)

==Point mass==
'''Point mass''' ('''pointlike mass''') is the concept, for example in [[classical physics]], of a physical object (typically [[matter]]) that has nonzero mass, and yet explicitly and specifically is (or is being thought of or modeled as) [[infinitesimal]] (infinitely small) in its volume or [[length|linear dimension]]s.
In the theory of [[gravity]], extended objects can behave as point-like even in their immediate vicinity.  For example, spherical objects interacting in [[3-dimensional space]] whose interactions are described by the [[Law of universal gravitation|Newtonian gravitation]] behave, as long as they do not touch each other, in such a way as if all their matter were concentrated in their [[center of mass|centers of mass]].<ref>{{cite book | title = Analytical Mechanics | first1 = Grant R | last1 = Fowles | first2 = George L | last2 = Cassiday | at = §6.2 Gravitational Force between a Uniform Sphere and a Particle | year = }}</ref> In fact, this is true for all fields described by an [[inverse square law]].<ref>{{cite book | first = I. | last = Newton | year = 1999 | translator-first1 = I. B. | translator-last1 = Cohen | translator-first2 = A. | translator-last2 = Whitman | title = The Principia: Mathematical Principles of Natural Philosophy | publisher = [[University of California Press]] | isbn = 0-520-08817-4 | at = p. 956 (Proposition 75, Theorem 35) }}</ref><ref name=NewtonMotteMachin1>I. Newton, A. Motte, J. Machin (1729), p. 270–271.{{cite book | first = I. | last = Newton | year = 1729 | translator-first1 = A. | translator-last1 = Motte | translator-first2 = J. | translator-last2 = Machin | title = The Mathematical Principles of Natural Philosophy | url = https://archive.org/details/bub_gb_Tm0FAAAAQAAJ | pages = [https://archive.org/details/bub_gb_Tm0FAAAAQAAJ/page/n354 270]–271 | publisher = [[Benjamin Motte]] }}</ref>