Velocity
Simple Explanation
Velocity is speed in a specific direction — the displacement covered per unit time. Two objects can have the same speed but different velocities if they're moving in different directions.
Why Do We Need It?
Velocity captures both how fast and which way something is moving, which matters whenever the direction of motion affects the outcome — like two cars approaching each other versus travelling the same way.
Formula
Velocity
velocity = displacement / time
Speed in a specific direction.
- velocity
- — rate of displacement, in metres per second (m/s), in a stated direction
- displacement
- — straight-line distance from start to finish, in a direction, in metres (m)
- time
- — time taken, in seconds (s)
When to use it: Whenever direction matters, not just how fast something is moving.
Worked Example
Calculate a drone's velocity
A drone flies 40 m due north in 8 s. What is its velocity?
Why Does This Work?
Because velocity is defined using displacement (which already includes direction), the result of this calculation always carries that same direction with it — unlike speed, which only ever gives a size.
Real-Life Example
Air traffic control
Air traffic controllers track both the speed and direction — the velocity — of every aircraft.
Knowing velocity, not just speed, is what lets them predict exactly where two aircraft will be and avoid collisions.
Practice
A swimmer's displacement is 25 m north in 10 s. What is their velocity? (Give the size only.)
MediumCommon mistake
Using distance instead of displacement when calculating velocity — if the path is not a straight line, this gives the average speed, not the velocity.
Quick Review
- velocity = displacement / time
- Velocity is a vector — it has both size and direction.
- Two objects can have equal speed but different velocity.