Motion graphs
Objective. Interpret gradients and signed areas on motion graphs.
- 1. Learn
- 2. Worked example
- 3. Practice
- 4. Feedback
- 5. Continue
Learn: the key idea
Motion graphs represent displacement, velocity or acceleration against time, and key features are read from gradients and areas. The gradient of a displacement-time graph gives velocity, and the gradient of a velocity-time graph gives acceleration, while the area under a velocity-time graph gives displacement. For example, a velocity-time graph showing constant velocity 4m/s for 5 seconds has area 20m, representing displacement, and zero gradient since acceleration is zero. Always check which graph you have before interpreting gradient or area, since the meaning changes between graph types.
Worked example
A velocity-time graph shows constant velocity 6m/s from t=0 to t=4s. Use this motion graph to find the displacement in this interval.
- 1Displacement equals area under a velocity-time graph
- 2The shape is a rectangle of height 6 and width 4
- 3Area=6×4
- 4Displacement=24m
Answer: 24m
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Practice
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Start practisingCommon mistake. Students read the area under a displacement-time graph as if it were useful, when only velocity-time graph areas give displacement. Always identify the graph's vertical axis before using gradient or area rules.
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