The same physical body in some conditions can be considered as a material point, and in other conditions – no. The ship sailing from the European port to coast of America – a material point. But if to consider the movement of a metal ball on a table in a cabin of this vessel, then it is impossible to consider the ship a material point already.
What is a material point
In mechanics mean the simplest physical model by a material point. It is about a body, the weight, the sizes which internal structure and rotation can be neglected if to follow conditions of a solvable task. The provision of this object in space is defined as the situation peculiar to a geometrical point.
In other words to ask about whether the material point has the sizes and weight, not quite correctly. It entirely is defined by initial conditions of a specific objective. Such parameters within the question considered by the researcher are just not taken into account.
Provisions of classical mechanics say that the mass of a material point is a constant in time. It does not depend on features of the movement of a point and on its interaction with other bodies.
The axiomatic approach accepted in classical mechanics allows to claim that the geometrical point to which the scalar size called weight can be delivered in compliance can be called material. This weight is constant, it is not depending on time and the provision of an object in space.
Whether such model is applicable to a concrete body? It will depend not so much on the body sizes how many from features and conditions of its movement. It is considered to be that at progress any solid body can be accepted to a material point. Its situation will coincide with the center of body weight. As at progress all points of a body move equally, for the description of such movement it is quite possible to manage the instruction on feature of movement of one its point.
Properties of a material point
The material point is capable to reserve mechanical energy in the form of kinetic energy at its movement in space or in the form of potential energy in interaction with the field. From this it follows that the material point is incapable of deformations. Such point it is possible to call only a rigid body.
The material point cannot rotate round its pivot-center, and this axis cannot change the direction in space.
The model where the movement of the body considered as a material point widely is described is used in a number of sections of mechanics.
With some reservations and as a first approximation the material point if desired can be considered as the molecule containing one atom (it is characteristic, in particular, of inert gases).
In a natural environment no material points, of course, exist. It is only model, scientific abstraction.