Statics is the action of one body on another. A force is either a push or a pull. A force tends to move a body in the direction of its action. The action of a force is characterized by its magnitude, by the direction of its action, and by its point of application. Thus, force is a vector quantity, because its effect depends on the direction as well as on the magnitude of the action. Forces are classified as either contact or body forces. A contact force is produced by direct physical contact; an example is the force exerted on a
Physical quantity generally well understood (everyone understands what is meant by "the frequency of a periodic phenomenon", or "the resistance of an electric wire"). The term "physical quantity" does not imply a physically "invariant quantity". "Length" for example is a "physical quantity", yet it is variant under coordinate change in special and general relativity. The notion of physical quantities is so basic and intuitive in the realm of science, that it does not need to be explicitly "spelled out" or even "mentioned". It is universally understood that scientists will (more often than not) deal with quantitative data, as opposed to qualitative data.