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Physics · 术语表

什么是 Gravitational potential energy?

又称: potential energy gravitational · reference level

Definition 9.4 High School Physics · 第 9 章 — Energy: Forms and Conservation

A body of mass mm at height hh (in m\mathrm{m}) above a chosen reference level stores the gravitational potential energy Ep=mghE_p = m g h, with g=9.81 N/kgg = 9.81\,\mathrm{N}/\mathrm{kg} — valid near the ground, where gg is effectively constant. Only differences of height matter: the level where Ep=0E_p = 0 is chosen freely.

示例

Example 9.5 (Water tower)

Each cubic metre (1000 kg1000\,\mathrm{kg}) of water stored 30 m30\,\mathrm{m} up a water tower holds 1000×9.81×30≈2.9×105 J1000 \times 9.81 \times 30 \approx 2.9 \times 10^{5}\,\mathrm{J} — about six tenths of the car’s kinetic energy above. Cities stockpile energy overhead.

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Definition 18.6 High School Physics · 第 18 章 — Mechanical Energy and Its Conservation

A body of mass mm at altitude zz, measured upward from a chosen reference level where z=0z = 0, stores the gravitational potential energy

Ep=mgz,g=9.81 N/kg.E_p = m g z, \qquad g = 9.81\,\mathrm{N}/\mathrm{kg}.

示例

Example 18.8 (A book on a shelf)

A 1.2 kg1.2\,\mathrm{kg} book sits 1.8 m1.8\,\mathrm{m} above the floor, itself 9.0 m9.0\,\mathrm{m} above the street. Reference at the floor: Ep=1.2×9.81×1.8≈21 JE_p = 1.2 \times 9.81 \times 1.8 \approx 21\,\mathrm{J}; in the street: Ep≈127 JE_p \approx 127\,\mathrm{J}. Falling to the floor releases 21 J21\,\mathrm{J} in both accounts.

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