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Take two toy cars of equal mass and stick a bar magnet on top of each (Fig. 6.32). Fix a metre scale on a smooth surface. Place the cars near the midpoint with like poles touching. Release them and record the time taken (using two stopwatches) and distance travelled by each before stopping. Repeat after adding equal masses to both cars. Did the cars travel equal distances in opposite directions? Plot distance versus mass. Analyse and discuss.
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The like poles repel, pushing the cars apart with equal and opposite forces (Newton's third law). Since the cars have equal mass, they get equal accelerations and travel roughly equal distances in opposite directions. Adding equal masses to both reduces the distances equally. Plotting distance against mass shows distance decreasing as mass increases, since heavier cars accelerate less.
