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        "text": "## 牛顿第二定律 · 控制变量\n光滑水平桌面俯视图，蓝色物块质量 0.50 kg。",
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        "text": "### 两组控制变量实验\n**A · 固定质量**\nm = 0.50 kg，F = 0.50、1.00、1.50 N。\n\n**B · 固定恒力**\nF = 1.00 N，m = 0.50、0.75、1.00 kg。\n\n每次先重置，再选中物块改质量，或选中橙色外力改“大小 F (N)”。\n运行到约 1.5 s，暂停读取 v 与 t。\n\n用图像斜率测 a，比较 a/F 与 am。水平方向向右为正。",
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