# 6. Vectors.

# 6. Vectors.#

Mass, temperature, energy, entropy, pressure, volume, and speed among many other quantities can be represented by a scalar, which is a simple number expressing the size or amount of something. Velocity, force, electric and magnetic fields, and acceleration each have *magnitude* and *direction* and therefore require two quantities to describe them, and they are called vectors. At school, you will probably have met a vector as an arrow drawn on a graph and which, therefore, has magnitude (length) and direction (angle). In biology, the idea is a related one, a vector being ‘something that carries’ and an infection is described as having a vector that causes its transmission from one creature to another.