Velocity
Speed in a stated direction. It is a vector, so changing direction changes velocity even if the speed stays the same.
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Analogy
Speed is what the speedometer shows. Velocity also needs the compass.
Example
Bus drives east at 10 m/s.Then it drives west at 10 m/s.Speed stays 10 m/s.Velocity goes from +10 to -10 m/s.
In practice
A car going round a roundabout at steady speed is still accelerating, because its direction keeps changing.
Practice
Flashcards
- What is the difference between speed and velocity?Velocity is speed in a given direction. Speed has no direction.
Questions people ask
Can an object have constant speed but changing velocity?
Yes. Velocity includes direction, so turning changes it. A car driving round a bend at a steady 20 m/s keeps the same speed, but its direction changes all the time. That means its velocity is changing, which is the same as saying it is accelerating.
Why can velocity be negative?
The sign shows direction. Pick one direction as positive, for example east. An object moving the opposite way has a negative velocity. The minus sign does not mean slower. A velocity of -10 m/s is exactly as fast as +10 m/s, just heading the other way.