Direct comparison
Speed vs velocity
Speed is how fast something is moving regardless of direction; velocity is speed together with a specified direction.
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Side-by-side comparison
| Dimension | Speed | Velocity |
|---|---|---|
| What it is | How fast an object moves. | How fast an object moves, and in which direction. |
| Quantity type | Scalar — magnitude only. | Vector — magnitude and direction. |
| Includes direction? | No. | Yes. |
| Based on | Total distance travelled over time. | Displacement (straight-line change in position) over time. |
| Can it be negative? | No — speed is never negative. | Yes — direction can be expressed as a sign. |
| SI unit | Metres per second (m/s). | Metres per second (m/s), with a direction. |
| Constant value while turning | Can stay constant around a bend. | Changes whenever direction changes, even at steady speed. |
| On a round trip | Average speed is total distance over time — non-zero. | Average velocity can be zero if you return to the start. |
| Example | A car’s speedometer reads 60 km/h. | 60 km/h heading west. |
Why direction matters
The difference looks small but matters in physics because acceleration is a change in velocity, not just speed. A car going around a roundabout at a steady 30 km/h is accelerating, because its direction — and therefore its velocity — is constantly changing, even though the speedometer reading never moves. Velocity is built on displacement (the straight-line change in position) rather than total distance, which is why a complete round trip can have zero average velocity but a substantial average speed.
Common questions
FAQ
Can speed be constant while velocity changes?+
Yes. An object moving at a steady speed around a circle has a constantly changing velocity, because velocity includes direction and the direction is always changing. This is exactly why circular motion involves acceleration even when the speed never varies — the velocity vector keeps turning.
Is velocity just speed with a direction?+
Essentially, yes. Velocity is the vector version of speed: it states how fast and in which direction. Speed is the magnitude (size) of the velocity. The deeper distinction is that velocity is built on displacement rather than total distance, so the two can differ over a journey that changes direction.
Can velocity be zero while speed is not?+
Over an interval, yes. If you walk out and return to your exact starting point, your displacement is zero, so your average velocity is zero — yet your average speed, based on the total distance walked, is clearly not zero. Speed counts every metre travelled; velocity counts only the net change in position.
Going deeper
