Scalar quantities are those quantities for which it is sufficient to know their magnitude, that is, their value, in order to determine them. Scalar quantities include time, time interval, average speed, mass, density, volume, etc. Vector quantities are those quantities for which it is necessary to know a) their magnitude, that is, their value, b) their direction, that is, their orientation (the straight line on which they lie) and their sense (their orientation along the straight line on which they lie). Vector quantities are represented by an arrow, the length of which is proportional to the magnitude of the quantity. Vector quantities include position, velocity, force, etc.