📚 Deriving Key Formulas from the A-Level Physics Data and Formula Booklet (January 2018) | A-Level物理数据与公式小册子（2018年1月）关键公式推导
Understanding where formulas come from deepens your grasp of physics and helps you apply them correctly. This article walks you through derivations of key equations found in the A-Level Physics Data and Formula Booklet (January 2018 edition), covering mechanics, waves, electricity, thermal physics and more.
理解公式的来源能加深对物理的掌握，并帮助你正确应用它们。本文将逐一推导A-Level物理数据与公式小册子（2018年1月版）中的关键方程，涵盖力学、波动、电学、热物理等领域。
1. Equations of Motion (SUVAT) | 运动学公式（SUVAT）
The SUVAT equations relate displacement (s), initial velocity (u), final velocity (v), acceleration (a) and time (t) for uniform acceleration. They are derived directly from the definitions of velocity and acceleration.
SUVAT方程描述了匀加速直线运动中位移(s)、初速度(u)、末速度(v)、加速度(a)和时间(t)之间的关系。它们直接由速度和加速度的定义推导而来。
ith the definition of acceleration: a = (v − u) / t. Rearranging gives the first equation:
从加速度的定义开始：a = (v − u) / t。重新排列得到第一个公式：
v = u + at
ity is (u + v) / 2 when acceleration is constant. Displacement is average velocity × time:
当加速度恒定时，平均速度为(u + v) / 2。位移 = 平均速度 × 时间：
