Mechanical balance of the material point

All solid bodies have a shape and some dimensions, but sometimes they can be treated in the simplest way, using the theoretical model of material point. In this case the shape and dimensions of the body are neglected and it is considered that all its mass is concentrated in a single point.

A type body material point is in mechanical equilibrium if:

is at rest
- or
it moves in a uniform straight line

relative to an inertial frame of reference.

The necessary and sufficient condition for the mechanical equilibrium of the material point is that the resultant of all forces is 0.