Motion graphs are one of the most visual topics in IGCSE Physics, and interpreting them correctly can earn easy marks once the underlying rules are understood. Distance-time and velocity-time graphs each reveal different information about how an object is moving.
1. Reading a Distance-Time Graph
On a distance-time graph, the gradient represents speed. A straight, sloped line indicates constant speed, a horizontal line indicates the object is stationary, and a curved line indicates changing speed, meaning the object is accelerating or decelerating.
2. Reading a Velocity-Time Graph
On a velocity-time graph, the gradient represents acceleration, while the area under the graph represents distance travelled. A horizontal line shows constant velocity, and a straight sloped line shows uniform acceleration or deceleration.
3. Calculating Area Under a Velocity-Time Graph
To find distance travelled from a velocity-time graph, students should break the shape into simple triangles and rectangles and sum their areas. This technique is frequently tested and rewards careful, methodical working.
4. Common Mistakes to Avoid
A frequent error is confusing what the gradient represents on each type of graph, or forgetting that a curved distance-time graph does not mean constant acceleration. Practising with labelled diagrams helps prevent this confusion during exams.
Frequently Asked Questions
What does a horizontal line on a distance-time graph mean?
A horizontal line on a distance-time graph means the object is stationary, since distance is not changing over time.
How do you find acceleration from a velocity-time graph?
Acceleration is found by calculating the gradient of the velocity-time graph, using the change in velocity divided by the change in time.
Conclusion
Once students can confidently link gradients and areas to physical quantities, motion graph questions become one of the more predictable and scorable sections of the IGCSE Physics paper.