📚 Internal Energy | 内能
Understanding internal energy is central to A-Level thermal physics. It explains why temperature, heat and work are related yet distinct, and it underpins the first law of thermodynamics.
理解内能是 A-Level 热物理的核心。它解释了温度、热量和功为何相关但又不同，并构成热力学第一定律的基础。
1. What Is Internal Energy? | 什么是内能？
Internal energy is the total energy stored inside a system by the particles that make it up. More precisely, it is the sum of the randomly distributed kinetic energies and potential energies of all molecules, atoms or ions in the system.
内能是系统内部组成粒子所储存的总能量。更准确地说，它是系统内所有分子、原子或离子的随机分布动能与势能之和。
The random kinetic energy comes from the translational, rotational and vibrational motion of particles. The potential energy arises from intermolecular forces between particles, which depend on their separation.
随机动能来自粒子的平动、转动和振动。势能来自粒子间的分子间作用力，其大小取决于粒子间距离。
Internal energy does not include the bulk kinetic energy of the whole object moving, nor the gravitational potential energy due to the object's position as a whole.
内能不包括物体整体运动时的宏观动能，也不包括物体整体位置决定的引力势能。
2. Kinetic and Potential Contributions | 动能与势能的贡献
The kinetic part of internal energy is directly linked to temperature. For an ideal gas, temperature is a measure of the average random kinetic energy per particle.
内能中的动能部分与温度直接相关。对于理想气体，温度是每个粒子平均随机动能的量度。
The potential part becomes important in solids and liquids because particles are close enough for intermolecular forces to store energy. When particles are pulled apart or pushed together from their equilibrium positions, their potential energy
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