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数学 / 牛顿《原理》数学部分 / Proposition 3 · measuring force geometrically

命题 3 · 用几何量读力

Force is read from how far the orbit falls away from the tangent in a small time.

力从轨道在极短时间内偏离切线的距离里读出来。

Proposition 3 · measuring force geometrically shows how motion can be read by areas, tangents and departures from tangents.

命题 3 · 用几何量读力 说明运动可以由面积、切线和切线偏离量来读。

Compare the tangent continuation with the actual curved path.

比较切线延长和真实曲线路径。

The departure is small, but its ratio to the squared time is the force clue.

偏离很小,但它和时间平方的比例给出力的线索。

与阿基米德穷竭法 archimedes-selections/overview、极限思想史 math-meta/topic-limit-history、微积分发明史 math-meta/topic-calculus-invention、柯西严格化 cauchy-cours/overview 和牛顿代数面 newton-arithmetica/overview 对读。