首先，我们必须了解蒸汽机，通过观察它的每一个部分了解它的工作原理。

First you have to understand steam, and how it works by looking at each part of the machine.

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例如，早在热动力学解释了蒸汽机操作的物理原理之前，蒸汽机已广泛存在。

The steam engine, for example, was commonplace before the science of thermodynamics elucidated the physical principle underlying its operations.

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气体膨胀时能做功这个原理被用在蒸汽机上。

The principle that gas can do work while expanding has been applied to the steam engine.

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