Point Particles

Pretty much all physical objects have volume, i.e. each object occupies some region of space. It turns out, however, that modelling objects with volume is a very difficult task. This is why we often resort to modelling objects as infinitesimally small point particles, with no size.

Definition: Point Particle

A point particle is a model of a physical object as an infinitesimally small point without any size.

Obviously, this is a very rough approximation. After all, both you, the car you drive, the Earth and so on are certainly not infinitesimally small and certainly occupy some volume. Nevertheless, this approximation is very accurate in many cases because, when viewed from a sufficiently great distance, objects behave more or less like point particles. Similarly, if the sizes of the objects are much smaller than the distances between them, objects can also be modelled by point particles quite well. Whenever this accuracy is not sufficient, we resort to modelling objects as collections of a very large number of point particles, which is not far from the truth given that all matter is made up of tiny atoms and molecules.