[Physics Class Notes] on Unit of Displacement Pdf for Exam

The displacement of an object is the change in the position of the object in a certain direction. Displacement is motion in one direction and since it depends on the direction of movement of an object, it is a vector quantity. It is usually denoted by “d” or “s”. Displacement is usually measured along a straight line. The S.I. the unit of Displacement is the meter. Since displacement is a vector quantity, it can be positive or negative.

Can Displacement be Zero?

To answer this question, let’s think of an example. Rina starts walking from your house towards her school and at the end of the day, she walks back to her house. She traversed a total path of, let’s say, 5 km but she came back to the same place she started from. So, her direction of movement starts from a point to the destination and the direction of movement back from the destination is opposite and the length covered is the same, that is, she comes back to the original starting point. Since displacement is a vector quantity, even though she covered a length of 5 kilometers, her net displacement is zero.

Examples

Let’s solve some examples to get a clearer idea of displacement. 

1. Harry goes for a jog every day in a park that is square in shape with each side equal to 200 meters. What is his displacement after one round of jogging?

Ans: Since displacement depends upon the initial and final points in the position of an object, even if the total distance traveled by Harry is 200 × 4 m = 800 m, he comes back to his starting point after one round of jogging, so his initial and final positions are the same, therefore, his net displacement is zero.

2. A vase is moved from the north end of a house to 150 cms towards the east, then it is moved south for 50 cms and then another 150 cms towards the west. What is the net displacement of the vase?

Ans: If the starting point is considered as A, the position of displacement towards the east to be B, then towards south be C and finally towards the west as D, then it follows as:

                               150m

                    A   →  B

                            ↓50m

                        D    ←     C

                    150m

Therefore, the net displacement is to be calculated from point A to point D, which is equal to the distance between point B and point C, ie, 50 m. Hence, the net displacement of the vase is 50 m.

Where is the Concept of Displacement Used?

The concept of displacement is very important to measure the dynamic motion of objects that are vector quantities, that is, they have a direction of motion. 

In one dimensional motion, it is used notably in the calculation of velocity, acceleration (and retardation) and upward or downward motions of objects under gravity. Just like displacement, vector quantities such as velocity and acceleration of an object can also be positive or negative depending on the displacement of the object.

In three dimensional motion, displacement finds its uses in the calculation of force and linear momentum as well as the practical applications of force and momentum such as friction, work, power and energy ( kinetic and potential).

It also has applications in the field of fluid dynamics.

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