Speed, velocity and distance-time graphs
This is Cambridge International IGCSE Physics 0625, an international course separate from the Egyptian Baccalaureate / Thanaweya Amma and not a Year 3 course. We will build the ideas one small step at a time: calculate speed, compare it with velocity, and read what motion graphs are telling us.
Speed answers “how much distance each second?”
Speed tells us how quickly distance is covered. A fast object covers a lot of distance in a short time; a slow object covers less. Speed is distance travelled divided by the time taken: v = s ÷ t. The symbol v is used for speed, s for distance and t for time.
Open the worked example
A runner covers 150 m in 20 s. Write the equation, substitute the values with units, then divide: v = 150 m ÷ 20 s = 7.5 m/s. The unit m/s means “metres each second”. Check: 7.5 m/s × 20 s = 150 m.
Quick check: A toy car travels 24 m in 6 s. What is its speed?
Think, then reveal: v = s ÷ t = 24 m ÷ 6 s = 4 m/s.
Explore speed and motion graphs
Change the journey and calculate its average speed
Try different values. Remember that distance ÷ time gives speed.
average speed = 600 m ÷ 300 s = 2.00 m/s
Spot the motion in two graphs
Choose a kind of motion. Compare the distance-time graph with the speed-time graph: the same horizontal line can mean different things on each graph.
Constant speed: Distance increases in a straight line; speed stays above zero and constant.
Quick check: a flat distance-time line means stopped; a flat speed-time line above zero means moving steadily.
Practise, then read the explanation
Try each question first, open its hint if you need help, then submit to see the worked reasoning. You can retry any question without losing the others.
Optional hint
Speed tells you how much distance is covered in each unit of time.
This original interactive lesson and practice set are aligned to Cambridge IGCSE Physics 0625 syllabus objectives 1.2.1–1.2.6. Source reading: Physics-0625 Volume A, Lesson 3, PDF pages 21–26 (printed pages 13–18). The next lesson develops acceleration and uses the area under a speed-time graph.