ABSTRACT
In order to specify completely certain physical quantities, such as temperature, energy and mass, it is necessary to give only a real number. These quantities are referred to as scalars. In order to specify completely certain other physical quantities, such as force, moment, velocity and acceleration, it is necessary to give both their magnitude (a nonnegative number), their direction and their sense. These quantities are referred to as vectors. They may be represented in a three-dimensional, Euclidian space by directed line segments (arrows) whose length is proportional to the magnitude of the vectors and whose direction and sense are those of the vectors.
