A trolley moves past a metre scale at nearly steady speed. Students can record repeated runs with a fixed camera and extract individual frames. Available equipment and procedure options: Read the scale position in each frame, subtract positions and divide by the timestamp difference. Design an investigation of how the time interval between selected frames affects the spread of calculated speeds. Include a reasoned hypothesis, an appropriate range, controls, repeat measurements, a results table or graph, and one specific limitation and safety measure. Do not invent experimental results.

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Vary the time interval between selected frames; measure the spread of calculated speeds. Predict Longer intervals should reduce the relative effect of reading position, provided the trolley speed stays steady. Keep camera position, target trolley speed, scale and position-reading rule constant, repeat each setting, and use the evidence to test the prediction. State a testable research question linking the time interval between selected frames to the spread of calculated speeds, rather than asking vaguely which arrangement is best. A suitable prediction is: Longer intervals should reduce the relative effect of reading position, provided the trolley speed stays steady. Justify that prediction scientifically: The same absolute position-reading uncertainty is a smaller fraction of a larger displacement. This is a hypothesis to test, not a result that the experiment must produce. Use 0.04, 0.08, 0.12, 0.16 and 0.20 s as the planned independent-variable settings. Measure the response using the supplied equipment: Read the scale position in each frame, subtract positions and divide by the timestamp difference. Record quantities with units before calculating any derived result. Keep camera position, target trolley speed, scale and position-reading rule constant. This isolates the proposed cause; changing these conditions at the same time would allow competing explanations for any difference. Take at least three independent trials at each setting, resetting the apparatus each time. Tabulate the setting, individual responses and mean; plot the mean response against the changed quantity and show the range of repeated values. Evaluate this specific limitation: Perspective distortion can bias every displacement; keep the scale in the trolley's plane and the camera perpendicular. More repeats alone do not necessarily correct a biased method. Protect participants and equipment by this precaution: Use a slow trolley with an end stop, away from table edges.

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