Relacionar Columnas - newton's laws of motionVersión en línea - newton's laws of motion por Lindsay Saravia 1 Force equals mass times acceleration. 2 Law of action and reaction. 3 The principle of inertia. It indicates that when a body is at rest, or describes a movement with the characteristics of MRU, the forces applied to it have a null result. Whenever one body exerts a force on another, this second exerts an opposite of equal intensity and direction but opposite sense on the first. This is the fundamental formula of dynamics, and it comes from assuming a body at rest on a horizontal surface, which is subject to a force parallel to that surface, being able to dispense with friction: we will see that the body starts moving at a constant acceleration.