What Is Displacement? Definition, Units, and Practical Examples
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.
To know more about displacement and get important questions, notes and sample papers and much more, hop on to Vedantu's website that offers explanations and examples which are solved in detail. You can get all the resources you need for free! Download now and start your preparation with Vedantu.
FAQs on Unit of Displacement: SI and CGS Units
1. What are the standard units used to measure displacement in Physics?
The standard units for measuring displacement depend on the system of measurement being used.
- The SI unit of displacement is the meter (m).
- The CGS (Centimeter-Gram-Second) unit of displacement is the centimeter (cm).
2. What is the primary difference between displacement and distance, particularly regarding their units and nature?
While both displacement and distance measure length and share the same SI unit (meter), their fundamental difference lies in their nature. Displacement is a vector quantity, meaning it has both magnitude and direction. It measures the net change in position. In contrast, distance is a scalar quantity, having only magnitude. It represents the total path covered, regardless of direction. Therefore, distance can never be negative, but displacement can be.
3. How is displacement calculated using a formula?
Displacement is calculated as the change in an object's position. The formula for displacement (represented by Δx or s) is:
Δx = xf - xi
Where:
- xf is the final position of the object.
- xi is the initial position of the object.
4. Why can displacement be zero or negative, whereas distance is always positive?
Displacement can be zero or negative because it is a vector that considers direction.
- Zero Displacement: An object has zero displacement if it returns to its starting point. For example, after one complete lap around a circular track, the distance covered is the circumference of the track, but the displacement is zero because the final position is the same as the initial position.
- Negative Displacement: Displacement is considered negative when an object moves in the opposite direction relative to a predefined positive direction or origin. If moving right is positive, moving left results in negative displacement.
5. In which real-world applications is the concept of displacement more important than distance?
Understanding displacement is crucial in many fields where the net outcome of motion matters more than the path taken. For example:
- Navigation and Aviation: A pilot needs to know the displacement from the origin to the destination to plot the most efficient flight path. The total distance flown might be longer due to wind or air traffic control, but the goal is to cover the displacement.
- Physics and Engineering: In calculating work done by certain forces or analysing projectile motion, the net displacement of an object is a key variable, not the meandering path it might have taken.
6. Is the unit of displacement, the meter, a fundamental or a derived unit?
The SI unit of displacement, the meter (m), is a fundamental unit. In the International System of Units (SI), there are seven fundamental units that form the basis for all other units. The meter is the base unit for length. Since displacement is a measure of length (the change in position), its unit is fundamental and not derived from a combination of other base units like velocity (m/s) or acceleration (m/s²).
7. How does the unit of displacement apply when working with position vectors in 2D or 3D space?
In two or three dimensions, an object's position is described by a position vector (r). The displacement is the change between the final and initial position vectors (Δr = rf - ri). The resulting displacement is also a vector. The unit for each component of the position vectors (e.g., in x, y, and z coordinates) is the meter (m). Consequently, the magnitude of the final displacement vector is also measured in meters, ensuring the concept and its unit remain consistent across dimensions.
