Speed vs Velocity — What's the Difference?
Speed
Speed is how fast an object moves, regardless of direction. It is the rate at which distance is covered over time, and it is always a non-negative number.
Unit: meters per second (m/s)
Example: A car speedometer reading 90 km/h reports speed. It tells you nothing about which direction the car is heading.
Velocity
Velocity is speed with a direction attached. It is the rate of change of displacement, and because displacement is a vector, velocity is a vector too.
Unit: meters per second (m/s), with direction
Example: Saying a plane flies at 800 km/h east states a velocity — the same speed pointed in a specific direction.
Key differences
| Aspect | Speed | Velocity |
|---|---|---|
| Quantity type | Scalar — magnitude only, no direction | Vector — magnitude plus direction |
| Sign | Never negative; zero or positive | Can be negative, indicating direction opposite the chosen positive axis |
| Round trip | Stays positive because distance was covered | Averages to zero if you return to your starting point, since displacement is zero |
| Circular motion | Constant for uniform circular motion | Continuously changing because direction keeps changing |
| Speedometer vs GPS | What a speedometer shows | What navigation needs — speed plus heading |
In everyday speech people say velocity when they mean speed. The test is simple: if the direction matters to the answer, you need velocity. A satellite in steady circular orbit has constant speed but its velocity changes every instant, because its direction of motion keeps turning.