The definition of a moment as the product of a force times a distance is equivalent to stating that it is the product of two vectors, a force vector and a displacement vector.

The method of adding or subtracting vectors has been defined by the parallelogram law, and multiplication of a vector by a scalar presents no new problems, it being necessary only to multiply the magnitude of the vector by the scalar and to leave the direction unchanged. When we come to the product of two vectors, however, there are several possible definitions which might be used. Two vector products are commonly employed and are of importance in the field of mechanics.