In physics, there is a concept termed ‘vector.’ A vector has two quantities —magnitude and direction. Force is an example of a vector; accordingly, force has the properties of both magnitude and direction, which can be quantified. The original treatise, Philosophiae Naturalis Principia Mathematica (The Mathematics Principles of Natural Philosophy), authored by Sir Isaac Newton and published by Benjamin Motte in 1687, best illustrates the vector properties of force through description of Newton’s Laws of Motion. Newton’s third law of motion states “for every action (force) in nature there is an equal and opposite reaction.” By the expression equal, Newton describes that the magnitude of the forces must be the same and, through the phrase opposite, he refers to the direction of the forces. This is a basic concept in physics and can be found in nearly every physics text. For example, two such books in which the concept of force is clearly defined, along with its application in Newtonian mechanics are: (i) Forensic Biomechanics by Jules Keisler, Michael Taylor and Debra Carr, published by Wiley-Blackwell in 2013; and, (ii) Biomechanics, Concepts and Computation by Cees Oomens, Marcel Brekelmans and Frank Baaijens, published by Cambridge University Press in 2009.
Biomechanical Engineering—Vectors