What is Displacement?
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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FAQs on Unit of Displacement
1. Discuss the reason behind displacement can be negative and zero?
Displacement can be negative but it cannot be negative always. Displacement is negative due to its vector quantity as it contains direction and magnitude. When the magnitude of the body or object remains the same but travels in the opposite direction which gave negative displacement. If the direction remains the same for the objects then it will be a positive displacement. The reason behind zero displacements is that when the object starts from an initial position and comes back to the initial position after the round trip, in that case, there are zero displacements.
2. How distance is different from displacement?
The distance is a vector quantity whereas the distance is a scalar quantity. The meaning of distance is how much ground has been covered by the object. Whereas the displacement means the shortest distance covered by the object. The displacement is along a straight line whereas in distance it is not necessary to be a straight line. The unit of both the distance and displacement are the same in both the measuring system. Another important difference is that distance cannot be zero but displacement can be zero. For example, the round trip in case of displacement is zero because it depends upon the shortest distance between the initial and final position as in the case of the round trip the object came back to its initial position therefore displacement can be zero.
3. What is the difference between displacement and distance?
Displacement is the change in position of an object which means “how far an object is from the initial point of motion” whereas distance is defined as the total path transversed by an object between the initial and final states of the object, i.e, “how much longer an object has covered while in motion”. While displacement is a vector quantity, distance is a scalar quantity which means that, unlike displacement, distance will always be a positive quantity and will only depend upon the magnitude and not on the direction of the object.
4. How are distance and displacement similar?
The only point of similarity between distance and displacement is that their S.I. units are the same, i.e, meter.
5. Why can displacement be a negative quantity?
Since displacement is a vector quantity which depends upon the magnitude as well as the direction of motion of an object, displacement can be positive, negative or zero depending upon the position of the object. For example, if a person starts from a point A towards a point B which is, let's say, 3 kms, and then walks back to another point C along the same line but C is behind point A by another 2 kms. Then the total distance covered will be 3+3+2 kms, i.e., 8 kms but the net displacement will be -2 kms.
6. How is displacement calculated?
Displacement is calculated on the basis of the position of an object with reference to the initial point of motion. In other words, it can be calculated as the shortest distance between starting and ending points.
7. What are the units of displacement?
The S.I. unit of displacement is meter and is denoted by “m”, whereas the CGS unit of displacement is centimeter which is denoted by “cm”.