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Physics · 术语表

什么是 Power？

又称： watt · power mechanical · horsepower

Definition 9.15 High School Physics · 第 9 章 — Energy: Forms and Conservation

Power is the rate at which energy flows, $P = E/t$ , measured in watts ( $\mathrm{W}$ ), with $1\,\mathrm{W} = 1\,\mathrm{J}/\mathrm{s}$ . Energy is an amount, power a flow — a bathtub versus its tap.

示例

Example 9.16 (Kettle versus human)

A $2200\,\mathrm{W}$ kettle running $150\,\mathrm{s}$ uses $E = 2200 \times 150 = 3.3 \times 10^{5}\,\mathrm{J}$ . A human runs on about $10\,\mathrm{MJ}$ of food per day, an average $1.0 \times 10^{7}/86\,400 \approx 116\,\mathrm{W}$ : you idle like a bright old light bulb.

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Definition 17.13 High School Physics · 第 17 章 — Work of a Force

The power of a force is the rate at which it works, $P = W/\Delta t$ , in watts ( $\mathrm{W} = \mathrm{J}/\mathrm{s}$ ) — the same watt as in Chapter 12. A pre-SI unit survives on engine badges: the horsepower, $1\,\mathrm{hp} = 736\,\mathrm{W}$ .

示例

Example 17.15 (Crane)

A crane hoists a $600\,\mathrm{kg}$ pallet at a steady $0.90\,\mathrm{m}/\mathrm{s}$ : the cable’s force equals the weight, $mg = 5.89 \times 10^{3}\,\mathrm{N}$ , so $P = Fv = 5890 \times 0.90 \approx 5.3\,\mathrm{kW} \approx 7.2\,\mathrm{hp}$ — a seven-horse team in a steel box.

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