Read a distance–time graph
This invented journey moves along a straight path without turning back. Plot time horizontally and total distance travelled vertically.
What happens from 20 to 30 seconds?
Join consecutive points with straight segments. Label both axes and units.
📝 Work one segment
From 0 to 20 seconds, distance increases by 40 m. Speed = distance change / time change = 40 / 20 = 2 m/s.
From 20 to 30 seconds, the distance stays at 40 m: the traveller is stopped. From 30 to 50 seconds, speed is 60 / 20 = 3 m/s. A steeper segment indicates greater speed on these axes.
📊 Compare averages
Total distance is 100 m and total time is 50 s, including the stop. Overall average speed is 2 m/s. Averaging the two moving speeds without accounting for time gives the wrong journey average.
Explain in words what each segment shows. If a graph shows position instead of total distance, downward segments can represent motion back toward an origin; do not confuse the two graph types.
✅ Check your understanding
Speed from 40 to 50 seconds?
Overall average speed?
✏️ Try a changed journey
Suppose the traveller covers the same 100 m but stops for 20 seconds instead of 10. Moving times stay unchanged. Find total journey time and average speed. Explain whether the moving speeds changed.
🔑 Worked answer
Total time increases from 50 to 60 seconds. Average speed = 100 / 60 ≈ 1.67 m/s. The moving speeds remain 2 and 3 m/s; only the stop changes.