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Readnary original study guide
Learn speed, acceleration and motion graphs through worked calculations and 12 original questions with explained answers.
Original AI-assisted Readnary material. Not independently academically reviewed; answers may contain errors. Check important results against your course materials.
Selected content from Physics 0625 section 1.2 for 2026-2028 exams. The guide covers straight-line distance-time and speed-time graphs, including constant-acceleration areas. It is not a complete motion or practical-skills course.
| Quantity | Meaning | Equation or graph clue |
|---|---|---|
| Average speed | Total distance per total time | distance / time, in m/s |
| Acceleration | Change of velocity per time | (final velocity - initial velocity) / time, in m/s2 |
| Graph area | Distance from a speed-time graph | Area between curve and time axis, in m |
Speed tells you how much distance is travelled per unit time. For a whole trip, add every distance and divide by the whole elapsed time, including a stop unless the question excludes it. Velocity also specifies direction; two journeys can have the same speed but different velocities. Use consistent units before calculating: 2 minutes is 120 seconds, so 240 m in 2 minutes gives 2 m/s, not 120 m/s.
The gradient of a straight section on a distance-time graph is speed. A horizontal section has zero speed; a steeper rising section represents a greater speed. For a curved section, the gradient changes, so the speed changes. A distance-time graph cannot fall if its vertical axis really is total distance travelled. A graph of displacement from a starting point can fall, because the object may head back towards the start. Read the axis label before describing motion.
The gradient of a speed-time graph is acceleration. A horizontal line above zero represents constant speed, while a rising line represents increasing speed. A falling line represents deceleration and has a negative gradient. The area under the graph gives distance travelled: use a rectangle for constant speed or a triangle for a straight increase from zero. When the line starts above zero and rises, split the area into a rectangle plus a triangle.
An acceleration answer needs m/s2, because it describes a velocity change in m/s each second. A speed-time graph can slope down without the object travelling backwards: it may still have positive speed while slowing. A negative velocity on a velocity-time graph is different and indicates the chosen opposite direction. Keep speed, velocity, distance and displacement distinct, and check whether a question asks for a section or the whole journey.
A student walks 180 m in 90 s, waits 30 s, then walks another 120 m in 60 s. Find the average speed for the whole trip.
A speed-time line rises uniformly from 4 m/s at 0 s to 16 m/s at 6 s. Find the acceleration.
A vehicle starts from rest, increases speed uniformly to 12 m/s over 5 s, then travels at 12 m/s for 4 s. Find its distance.
Try each question before opening its answer. Numerical answers should include your working.
150 / 30 = 5 m/s. Divide distance by time and include the speed unit.
Convert 6 km to 6000 m and 10 minutes to 600 s. Speed = 6000 / 600 = 10 m/s.
Distance = 300 m; elapsed time = 20 + 10 + 50 = 80 s. Average speed = 300 / 80 = 3.75 m/s.
Distance from the start is not changing during that interval, so the object is at rest.
The second: gradients are 4 m/s and 8 m/s respectively. A steeper rise over less time means greater speed.
(15 - 3) / 4 = 3 m/s2, assuming the direction of motion stays the same.
(8 - 20) / 6 = -2 m/s2. The negative sign indicates deceleration in the chosen direction.
The rectangular area is 7 x 9 = 63 m.
The triangular area is 0.5 x 8 x 10 = 40 m.
Area = rectangle 4 x 3 plus triangle 0.5 x 3 x 6 = 12 + 9 = 21 m.
No. Total distance travelled accumulates and cannot decrease. A displacement graph may slope down when the object moves towards its starting point.
No. Its speed remains positive; it is slowing down. Direction cannot be read from speed alone.
Averages use total distance divided by total elapsed time, not the mean of two speeds. A speed-time gradient is acceleration, while its area is distance. A falling speed line does not by itself mean backwards motion.
Physics · IGCSE · STUDY GUIDE
Learn speed, acceleration and motion graphs through worked calculations and 12 original questions with explained answers.
Read the original Readnary guide in PDF view or use the web lesson above. Try the questions before revealing their explained answers.