Grade 10 · Physical Sciences
Motion in one dimension
Distinguish distance from displacement and calculate average speed, velocity and acceleration.
Scalars and vectors
Distance is the total path length and has no direction. Displacement is the change in position and includes direction. Choose a positive direction before calculating velocity.
Use consistent units
Convert kilometres to metres and minutes to seconds. Average speed uses total distance; average velocity uses displacement. Acceleration is the change in velocity divided by the time interval.
Formula sheet
- Average speed = total distance / time
- Average velocity = displacement / time
- Average acceleration = (final velocity - initial velocity) / time
Worked example
A learner walks 60 m east and then 20 m west in 40 s. Find average speed and average velocity.
- Total distance = 60 + 20 = 80 m.
- Choose east as positive. Displacement = +60 - 20 = +40 m.
- Average speed = 80 / 40 = 2 m/s.
- Average velocity = +40 / 40 = +1 m/s, or 1 m/s east.
Try it yourself
1. A car changes velocity from 5 m/s east to 17 m/s east in 4 s. Find average acceleration. Check answer
Take east as positive: (17 - 5) / 4 = 3 m/s² east.
2. A runner returns to the starting point after one lap. What is displacement? Check answer
Zero, although the distance travelled is the full length of the lap.
Common mistake: Average velocity is not always equal to average speed. A return trip can have zero average velocity.