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1 Primary & Middle School Mathematics1–9 年级在线 2 High School Mathematics10–12 年级在线 3 University Mathematics — Year 1本科一年级在线 4 University Mathematics — Year 2本科二年级在线 5 University Mathematics — Year 3本科三年级在线

1 Primary & Middle School Physics1–9 年级在线 2 High School Physics10–12 年级在线 3 University Physics — Year 1本科一年级在线 4 University Physics — Year 2本科二年级在线 5 University Physics — Year 3本科三年级在线

1 School Chemistry — Grades 1 to 121–12 年级在线 2 University Chemistry — Year 1本科一年级在线 3 University Chemistry — Year 2本科二年级在线 4 University Chemistry — Year 3本科三年级在线

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1 Primary & Middle School Earth and Space Sciences1–9 年级在线 2 High School Earth and Space Sciences10–12 年级在线 3 University Earth and Space Sciences — Year 1本科一年级在线 4 University Earth and Space Sciences — Year 2本科二年级在线 5 University Earth and Space Sciences — Year 3本科三年级在线

1 Markets I: The Ecosystem and Exchange-Traded Markets市场在线 2 Markets II: Rates, FX and Credit市场在线 3 Markets III: Commodities, Energy and Crypto市场在线 4 Quantitative Methods方法在线 5 Derivatives and Volatility衍生品在线 6 Rates, Credit, XVA and Risk利率、信用与风险在线 7 Research Craft: Predictors, Backtests, Measurement, Portfolios研究在线 8 Strategies I: Equities and Futures策略在线 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desks策略在线 10 Microstructure and Execution交易执行在线 11 Market Making and High-Frequency Trading做市在线 12 Machine Learning for Markets机器学习在线 13 Low-Latency Software技术在线 14 Networks, Hardware and Trading Infrastructure技术在线 15 Research, Data and Risk Platforms技术在线 16 The Desk and the Firm公司运营在线 17 The Industry: Firms, Roles and Careers职业发展在线 18 Interviews I: Maths, Probability and Speed职业发展在线 19 Interviews II: Markets, Trading Games and the Final Round职业发展在线 20 Interviews III: Code职业发展在线

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Physics · 术语表

什么是 Measuring a length？

又称： measure · unit

Definition 7.3 Primary & Middle School Physics · 第 7 章 — Measuring Length

To measure a length is to count how many times a chosen unit — a step, a hand span, a small stick — fits along it, end to end with no gaps and no overlaps. The answer is a number of units: “the room is $12$ steps long.”

The same wall, paced twice: 12 small feet, or 8 big feet. Different feet, different numbers — the wall did not change. — The same wall, paced twice: $12$ small feet, or $8$ big feet. Different feet, different numbers — the wall did not change.

示例

Example 7.4 (Try it: pace the room)

Cross your bedroom heel-to-toe, counting your foot-lengths. Ask a grown-up to do the same. You might count $18$ feet and the grown-up only $12$ — for the same room! Nobody counted wrong: your feet are shorter, so more of them fit. A measurement made with my foot cannot be checked with your foot.

Example 7.8 (Which unit for which job?)

Small things like a beetle, a stamp or your hand are measured in centimetres. Big things like a corridor, a bus or a swimming pool are measured in metres: the pool is $25\,\mathrm{m}$ long — imagine counting that in fingernail-widths! Choosing a sensible unit is half the work of measuring.

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