Length: defines position of a point in space and thereby describe the size of a physical system. Force: push or pull exerted by one body on another vector quantity with both direction and magnitude. Has mass, but a size that can be neglected. Rigid body lines of action of all forces intersect at a common point stiff body with negligible deformations. Parts of body remain fixed relative to each other. Material properties not considered in analysis of applied forces. Represents effect of a loading assumed to act at a point on a body. Reasonable if area over which load is applied is very small compared to overall size of body. Newtonian mechanics is used in statics to analyze particles and rigid bodies at rest, while neglecting forces associated with inertia and accelerations. Newtonian mechanics assumes that space, time, and mass are absolute quantities.