A Scalar quantity only has a magnitude whereas a Vector quantity has a direction as well as a magnitude.
For example time and distance are scalar quantities as they only have a magnitude, whereas displacement and velocity are vector quantities as they have both a magnitude and a direction:
Quantity Scalar or Vector Magnitude and Direction Unit
Time Scalar Just a magnitude Seconds
Distance Scalar Just a magnitude Metres
Displacement Vector Magnitiude and Direction Metres
Velocity Vector Magnitude and Direction Metres per Second
Displacement, as opposed to just distance, is the shortest distance form the start point and comprises a distance along with an angle or bearing, and Velocity is speed in a given direction.
On the displacement time graph, to the side, the displacment is shown by the orange arrow, which shows the shortest distance from the origin. This displacement should be given with a distance in metres as well as a direction, with an angle or bearing.
On the velocity time graph the minus figure does not indicate a minus speed; instead it indicates a direction relative to the start direction which is shown from the origin. In this example if we assume the the y axis corresponds to a direction angle of 90 degrees or East, then the initial velocity is around 45 degrees, or North East, which then changes to approximately 135 degrees and returns to a direction / angle that is the same as the origin at 30 seconds. The velocity continues on this same angle / heading for another 7 seconds or so then changes angle back to a direction of approximately 45 degrees, or North East to return to the same direction / angle / bearing as the start direction / angle / bearing at 50 sec.Finally to reiterate a number of final points:
The gradient of a distance time graph equals the speed- The gradient of a velocity time graph equals the acceleration
- The area under a velocity time graph equals the distance travelled
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