In physics, we frequently come across confusing terms, which may require further attention to understand for some people. Some of those terms are distance and displacement.
Actually, these two terms are used to express length. But in physics, it’s too rough to say length. Therefore, the term “length” needs to be detailed.
In our life, knowing the differences between displacement and distance is useful. It is educating and helps you be aware of what you are doing as we commonly use speedometers (in cars, motorcycles, and bicycles), rangefinders, laser measures, tape measures, etc, in which you are actually measuring either distance or displacement.
Without further ado, let’s explain the difference between them.
The Core Difference Between Distance Vs. Displacement
Distance is the total ground length passed by the body from the starting point to the final point. In contrast, displacement is defined as the shortest possible distance covered between those two points (starting point to final point. If you can imagine, displacement is actually defined as the straight line between those two points.
In the perspective of Physics, distance is considered as a scalar quantity because it has magnitude only and direction, whereas displacement is a vector quantity that has properties of magnitude and direction.
Understanding the Concept of Distance
When a body covers a distance without considering the direction of the object, that is known as distance. For example, a boy traveled from home to school and then to the zoo. If the distance from the school to home is 3km and the distance from school to the zoo is 2km. Therefore, the boy covered a distance of 5 km.
Understanding the Concept of Displacement
Displacement is a vector quantity having magnitude (short or long) and direction (positive or negative / back or forth).
So, the considering above example, the boy traveled a distance of 5km, but when it comes to calculating the Displacement, the same boy has a net displacement of 3km from home to the zoo.
When do the Distance and Displacement Have the Same Value?
This is the overlapping case between distance and displacement. Distance and displacement can be the same value when that body travels just straight to the final point. In this case, the value of distance and displacement are the same and they are positive.
Speed Relation with Distance
Speed is related to the distance covered by the body per unit of time. When we have to calculate the average speed of the body, we must know the value of distance and time. Therefore, the unit of speed will be a meter per second.
Velocity Relation with Displacement
To calculate the velocity, we must know the value of displacement and time. The average velocity means how the body has covered much net distance in a particular time. The unit of velocity is the same as the unit of speed which is a meter per second.
Covering the Distance in A Circular Path
If a motorcyclist is riding the motorbike at zero point with an average speed of 30 km per hour and has covered the distance of 15 km in half an hour, but when we have to calculate the displacement, the result will be zero.
Understanding Distance and Displacement through Examples
There is a mini-marathon race of 2 km in 10 minutes. Distance only can be positive, whereas Displacement can be both positive and negative. The boys have to start the race from zero point parks to zoo road, and then they have to get back to zero point. So, in that case, boys have to run 2 km, which is the overall distance, whereas Displacement will be zero because the net Displacement of boys is zero.
Instruments to measure the Distance and Displacement
To measure the Displacement and Distance of an object various types of devices are used. The instruments you select will vary depending on what you are measuring. The distance of an object is measured by a digital tape meter and measuring wheel. In contrast, displacement is measured by proximity sensors, laser range finder, and LVDT (linear voltage differential transformer).
Instruments to Measure the Displacement
1. Proximity sensor
A proximity sensor (displacement sensor) measures the displacement of an object from the reference point to the final point. The displacement sensor measures the velocity of an object and acceleration. In addition, to measure the displacement, the proximity sensors measure the dimensions, height, and width of an object.
2. Laser range finder
A laser range finder is also used to measure the displacement of an object. The laser finder emits electromagnetic waves. These electromagnetic waves are generated by the optical system of the laser range finder. Therefore, these electromagnetic waves collided with an object and returned to the device. So, that is how the laser range finder calculates the distance.
3. LVDT (linear voltage differential transformer)
The linear displacement of an object is measurable with LVDT. It is a type of electro-mechanical sensor it converts motion into current or voltage and calculates the displacement of an object.
Instruments to Measure the Distance
1. Measuring wheel
Measuring wheels or wheel measure is a handheld tool to the distance of an object; also known as the trundle wheel. It works by counting the total number of rotations of the wheel, and then by using the circumference of a circle, it calculates the distance from the first position to the last one. It is a device that measures the distance accurately, but if there is dirt or any material attached to the tire, it can give errors.
2. Tape measures
Another way to measure the distance of an object is by using a retractable tape measure. One type of tape measure can assist you to measure the distance up to 100 feet, even 300 feet. It is used to measure the length, width, and height of an object along with distance.
Comparison Table of Distance Vs. Displacement
| Distance | Displacement |
| 1. It is a physical quantity having only magnitude but no any direction and is termed as scalar quantity | 1. It is a physical quantity having both magnitude and direction and is known as vector quantity. |
| 2. A body covering total length in a particular time is known as distance. | 2. Net distance covered by the body or the shortest distance between the two points. |
| 3. When a body has motion, it always covers the distance. | 3. Displacement can be zero. If a body returns to its initial position, then the displacement is said to be zero. |
| 4. There is only a positive value for the distance. | 4. The value of displacement can be either positive or negative. |
| 5. The unit of distance is meter (m) | 5. The unit of displacement is meter (m) |