A vector quantity is one which has magnitude and direction. For example, velocity is a vector quantity (whereas speed is a scalar quantity).

Vectors are commonly used to describe linear translations.

• The vector a = $\left[\begin{matrix}a\\b\\c\end{matrix}\right]$ means $+a$ units parallel to the x-axis, $+b$ units parallel to the y-axis and $+c$ units parallel to the z-axis.
• The magnitude of a is $\sqrt{a^2+b^2+c^2}$
Vector addition is simple: you just add together the corresponding components of each vector; it is also easy to multiply a vector by a scalar - you simply multiply each component of the vector by the scalar. Multiplying vectors, however, is not so simple; there are different ways of multiplying vectors together - the two most commonly used are the scalar product (also called the dot-product) and the vector product (also called the cross-product).