Scalar Quantities and Vector Quantities

In previous page. we have just conclude our discussion on base and derived quantities. We will now shift our focus to scalar and vector quantities.

Physical quantities can also be divided into scalar quantities and vector quantities. Scalar quantities are the quantities that have no direction whereas vector quantities are the quantities that have direction.

Let’s see this example. A man run from his house to his friend’s house at an average speed of 20ms-1.  The distance between the 2 houses is 200m. How much time does he take for the journey?

The answer is, “It can’t be determined!”. We can’t determine the time taken for the journey because the direction of the motion is not given. It is not stated in the question that the man moved in a straight line. He may moved like the picture below or in any other path. Therefore, we are unable to calculate the time he took for the journey.

This example shows that for some physical quantities, direction is very important for us to make accurate calculation or prediction. A quantity with direction is called a vector quantity.

Before we start our discussion on scalar and vector quantities, it’s important for us to understand the word “magnitude”. What is the meaning of magnitude?

Let’s see this example.

A force is equal to -5N. The negative sign shows the direction of the force; Newton is the unit and the magnitude of the force is 5. Look at another example. A mass equal to 20kg. Kilogram is the unit and 20 is the magnitude.

The magnitude of a physical quantity is the greatness of the quantity or the size of the quantity. All physical quantities have magnitude.

For example, the greatness of the force is 5 and the size of the mass is 20.

So, we have learned that direction is very important in some physical quantities. Therefore, we can categorised physical quantities into 2 types, the scalar quantities and the vector quantities.

Scalar quantities are physical quantities that have magnitude only. Vector quantities are physical quantities that have magnitude and direction.

Examples of scalar quantities are distance, speed, density, mass, time and temperature.

Examples of vector quantities that you need to know in SPM include displacement, velocity, acceleration, momentum, force and impulse.

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