In mechanics interaction of bodies resulting in the change of motion is called a force. Further on there will be no referencies. Physical forces always occur as a result of interaction of a body or a physical point with another body. The forces resulting from the interaction of bodies in nature must always exist in couples. Very often one may not consider bodies as being the sources affecting the material point of forces.
Every body is accelrated under the action of other bodies.
Measure of this action is called a force. A force is the influence of one body on another resulting in the accelration of the latter. A force is the measure of interaction of physical bodies, that is the object of nature. The action of physical bodies on a physical point in question resulting in acceleration of the motion of this point is called a force. From now on a force may be considered a physical field which has length, motion, energy and even mass as it was discovered at the begining of the century.