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Physics · 术语表

什么是 Closed system; momentum conservation?

Definition 12.4 University Physics — Year 1 · 第 12 章 — Newton’s Laws of Dynamics

A closed system exchanges no matter with the outside. For a system of particles, the internal forces cancel in pairs (third law), and the total momentum P→=∑miv→i\vect P = \sum m_i\vect v_i obeys  ⁣dP→/ ⁣dt=∑F→ext\dd\vect P/\dd t = \sum\vect F_{\mathrm{ext}}: it is conserved when the external forces vanish (Chapter 19 develops this).

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