A force is an action of one body on another it has a point of application, magnitude, and direction. Multiple forces acting on a particle have the same point of application, so generally we only deal with forces defined with their magnitude and direction (remember: they"re vectors) Remember: magnitude is measured in newtons (n)/kilonewtons (kn) direction is defined as the line of action (infinite straight line), sense of the force, and angle is forms with a fixed axis. 2 forces acting on a particle can be replaced by a single force, r, the resultant (see in lecture 1 note: parallelogram law for the addition of 2 forces) Vectors are mathematical expressions possessing magnitude and direction. forces, displacements, velocity, accelerations, and momenta are all vectors. Vectors can be fixed or bound if they represent a force acting on a particle at a well-defined point, whereas a free vector can be moved anywhere in space.