A vector has both magnitude and   direction. A scalar is a magnitude only. In these notes, a vector is represented boldface, such as A. In the text, or when written by hand, a vector is shown with an arrow on top. Writing A (not bold, without an arrow), or |A| means the magnitude of the vector.

Pictorially, a vector is an arrow whose length equals the magnitude of the vector. Rules for multiplying a vector by a scalar are illustrated below: