Distance vs Displacement
5 Minutes
Distance vs displacement explained for students through everyday examples like taxi rides and school routes. An English science lesson.
- What distance means and why it is a scalar quantity
- What displacement is and why direction makes it a vector
- How displacement can be equal to distance or even zero
What this lesson teaches
Distance is the total length an object travels from the moment it starts moving until it stops, while displacement is the shortest straight-line length between the starting point and the ending point. Displacement includes both the length of that shortest path and the direction of movement.
Scalars and vectors
- A scalar quantity is a measurement that has only magnitude, which is its numerical amount.
- Distance is a scalar quantity, such as a vehicle traveling a length of 700 kilometers on its odometer.
- A vector quantity is a measurement that specifies both magnitude and a clear direction.
- Mentioning 700 kilometers towards the east or towards the north turns the measurement into a vector quantity.
Measuring paths to school
Traveling from a house to a school along curved streets illustrates the difference between these two measurements. If a thread is laid along the winding road and measured, the full route might equal five kilometers, which is the distance traveled. The straight line between the house and the school might be only two kilometers in a single direction, which is the displacement (idam peyarthal). Changing position between two places only counts the direct shortcut, not the extra roads taken.
How the two values compare
- Displacement will always be less than distance, or equal to distance when moving along a straight line.
- Displacement can never be more than distance because displacement is always the shortest possible path.
- In a straight 100-meter running race, distance and displacement are equal because the straight line is the shortest path.
- When a runner completes a full lap on a round track and stops at the starting point, displacement is zero while distance is not.
The taxi ride example
A taxi passenger who falls asleep might be driven through several streets and dropped off at the exact location where the trip began. The taxi meter shows that a real distance was traveled, and the vehicle consumed fuel to cover those streets. The displacement for the trip is zero because the final position is identical to the starting position. The driver calculates the trip based on distance, while the passenger's overall change in position is zero.