Finding g: free fall with an electromagnet, light gates and a data logger sim
Set the drop height of a steel ball under an electromagnet, time each fall with a light gate, record three times at six or more heights, plot h against t² and find g from its gradient; then drop a picket fence through a light gate and find g from the data logger's velocity–time graph, and time a 1 m drop by hand to see why a stopwatch cannot do it.
Kinematics · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model: from rest, h = ½ g t² (the area under the velocity–time graph), so h against t² has gradient g ÷ 2; a picket fence's velocity–time graph has gradient g. The ball and the card fall with g = 9.78 m/s² (Singapore's real value; exam sums use 10 N/kg) and a small air drag. The electromagnet lets go about 10 ms after the timer starts (chosen; a systematic error); the timer reads to 0.001 s, the logger to 0.00001 s, the stopwatch to 0.01 s; hand timing adds a reaction-time error with σ = 0.04 s at each press (chosen). Idealised: a thin beam, a straight fall, no spin or tipping.
- The steel ball (A, C) or the card (B): the part to watch
- Stands and clamps, electromagnet, light gates, metre rule, tray and catch box, power supply, switch box, data logger, stopwatch
Use it in your lessons
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