O-Level and SEC G3 Physics K323
P2: Kinematics
Connect motion quantities, graphs, gradients, areas, and equations without assuming constant acceleration unless justified.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Kinematics describes motion without first explaining its cause. The exam focus is precise definitions, one-dimensional graph interpretation, average quantities, acceleration, and the link between the area under a velocity-time graph and displacement.
Distance, displacement, speed and velocity
Distance is the total path length and is a scalar. Displacement is the directed change in position and is a vector. Speed is distance travelled per unit time, while velocity is displacement per unit time in a stated direction.
Average speed uses total distance divided by total time, including stops. A negative velocity represents motion in the chosen negative direction; it does not mean the object is moving slowly.
Acceleration and free fall
Acceleration is the rate of change of velocity. It can arise from a change in speed, direction, or both. Uniform acceleration means equal velocity changes in equal time intervals. Non-uniform acceleration gives a changing gradient on a velocity-time graph.
Near Earth, free-fall acceleration is approximately when air resistance is neglected. Choose a positive direction before using signs. A falling object may have positive or negative velocity depending on that choice.
Motion graphs
The gradient of a displacement-time graph gives velocity. A horizontal segment means rest, a constant non-zero gradient means uniform velocity, and a changing gradient means non-uniform velocity. The graph value itself is position relative to the chosen origin.
The gradient of a velocity-time graph gives acceleration. The signed area between the graph and time axis gives displacement for the K323 uniform-velocity or uniform-acceleration cases. Areas below the axis count negatively.
Formulae and relationships
| Relationship | Use |
|---|---|
| Find average speed. | |
| Find uniform acceleration. | |
| Find displacement from the graph. |
Worked examples
Example 1: A car increases velocity uniformly from to in . Find its acceleration and displacement.
- Acceleration: .
- The velocity-time area is a trapezium: .
- Therefore .
Answer: Acceleration ; displacement .
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Define distance, displacement, speed, velocity, and acceleration before choosing a relationship.
- Read gradient and area from motion graphs with their physical units attached.
- Use constant-acceleration equations only when the motion model justifies that assumption.
Official outcome coverage
K323 P2: 9 mapped outcomes, references P2(a), P2(b), P2(c), P2(d), P2(e), P2(f), P2(g), P2(h), P2(i). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Plan a motion investigation with a measured distance, reliable timing method, repeated trials, and a graph that answers the stated question.
Exam traps and retrieval check
Avoid these traps
- Using displacement instead of total distance for average speed.
- Calling every downward acceleration negative without declaring the positive direction.
- Reading graph height when the question asks for gradient or area.
Check from memory
What does a horizontal displacement-time graph show?
The object is at rest at a fixed position.
Can constant speed have changing velocity?
Yes, if direction changes, although K323 graph work here is one-dimensional.
What does area below a velocity-time axis represent?
Negative displacement in the chosen coordinate direction.
Pure versus Combined scope
Combined Physics revisits part of this core under CP2 Kinematics, but with reduced outcome scope. Combined students should follow the component checklist rather than assume every K323 outcome is assessable.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.