What is a particle? How can we consider an object as a particle?

(N/A) The concept of a particle is fundamental in mechanics.
$A$ particle is defined as a point-like object that possesses mass but has no dimensions (size).
Since a particle is dimensionless,it is an idealized concept and does not exist in reality.
$A$ particle can only undergo translational (linear) motion.
An object can be considered a particle in the following cases:
$(1)$ An object is treated as a particle if it moves in such a way that all its constituent parts cover the same distance in the same time interval (pure translational motion).
$(2)$ When the dimensions of an object are negligible compared to the distance it travels or the distance between it and another object,it can be treated as a particle.
Example: The Earth and the Sun are considered particles when calculating the gravitational force between them because the distance between them is vast compared to their sizes.