Scalar and Vector quantities

 In the world we know anything that can be measured is called a quantity. Joy and sorrow are not quantities but temperature is a quantity. Because joy and sorrow cannot be assigned a value by measuring them but temperature can be given a value by measurement. The temperature of your body is 37°C or 98.4°F. To express temperature a single number is sufficient, but there are many quantities which cannot be expressed by a single number completely, with its magnitude its direction has to be mentioned or more than one magnitude has to be mentioned so that they altogether can express definitely the magnitude and direction of the quantity. Position is a quantity of this type, to express this only the distance is not sufficient; its direction has also to be mentioned. The quantity which can be expressed only by a single number is called a scalar quantity, on the other hand the quantities for which direction has to be mentioned in addition to its magnitude are called vector quantities.

Besides temperature examples of scalar are time, length and mass. Because they can be expressed by a single number only. Besides position you will find the other examples of vectors are velocity and force. You will be introduced with velocity and force in the next chapter. Because to express these quantities, direction is to be mentioned along with its magnitude.

To differentiate vector quantities from scalar quantities they are written in bold font (e.g. x, y or A, B). In books or in computer printing it is easy to write anything in bold form. But when anyone writes on a paper then to express anything as vector, a small arrow is used over it (x,y or A, B).