📚 Year 9 SQA Engineering: Formula & Theorem Quick Reference Handbook | 九年级SQA工程公式定理速查手册
Welcome to your quick reference guide for the Year 9 SQA Engineering course. This handbook contains all the essential formulas, theorems and unit conventions you will need, presented in a clear bilingual format. Use it for revision, homework help or as a handy companion in the workshop and lab.
欢迎使用九年级SQA工程课程速查手册。本手册以清晰的双语形式收录了你需要掌握的所有核心公式、定理和单位规则，可用于复习、作业辅导或作为车间和实验室中的随身工具。
1. Units and Prefixes | 单位与前缀
Engineering relies on the International System of Units (SI). The base units are metre (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current and kelvin (K) for temperature.
工程学使用国际单位制 (SI)。基本单位有：长度米 (m)、质量千克 (kg)、时间秒 (s)、电流安培 (A) 和温度开尔文 (K)。
Large and small quantities are expressed using prefixes. The table below lists the most common ones you will meet in Year 9.
很大或很小的量用词头表示。下表列出了九年级最常用的词头。
| Prefix | Symbol | Factor |
|---|---|---|
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| centi | c | 10⁻² |
| milli | m | 10⁻³ |
| micro | µ | 10⁻⁶ |
For example, 5 kN = 5 × 10³ N = 5000 N, and 20 mm = 20 × 10⁻³ m = 0.02 m.
例如，5 kN = 5 × 10³ N = 5000 N，20 mm = 20 × 10⁻³ m = 0.02 m。
easured in newtons (N = kg·m/s²), energy in joules (J = N·m) and power in watts (W = J/s).
导出单位由基本单位组合而成。力用牛顿 (N = kg·m/s²)，能量用焦耳 (J = N·m)，功率用瓦特 (W = J/s)。
2. Basic Kinematics | 基本运动学
Kinematics describes how objects move, without considering the forces causing the motion. The key quantities are displacement, speed, velocity and acceleration.
运动学描述物体如何运动，而不考虑引起运动的力。关键量有位移、速率、速度和加速度。
v = s / t
速度 = 路程 ÷ 时间
Here v is average speed, s is distance travelled and t is the time taken. The SI unit is metre per second (m/s).
其中 v 为平均速度，s 为经过的距离，t 为所用时间。国际单位为米每秒 (m/s)。
a = (v − u) / t
加速度 = (末速度 − 初速度) ÷ 时间
Acceleration a is the rate of change of velocity. u is initial velocity, v is final velocity and t is time. The unit is m/s².
加速度 a 是速度的变化率。u 为初速度，v 为末速度，t 为时间。单位为 m/s²。
v = u + a t
v = u + a t
s = u t + ½ a t²
s = u t + ½ a t²
v² = u² + 2 a s
v² = u² + 2 a s
These three equations of motion work only when acceleration is constant. They allow you to calculate any unknown if you know three of the four variables u, v, a, t and s.
以上三个运动方程只适用于匀加速直线运动。若已知 u、v、a、t 和 s 中的任意三个量，便可求出未知的第四个量。
3. Newton's Laws of Motion | 牛顿运动定律
Newton's three laws form the basis of classical mechanics. The first law states that an object remains at rest or in uniform motion unless acted upon by an external force.
牛顿三定律构成了经典力学的基础。第一定律指出，物体将保持静止或匀速直线运动状态，除非有外力迫使其改变。
The second law relates force, mass and acceleration.
第二定律将力、质量和加速度联系起来。
F = m a
合力 = 质量 × 加速度
F is the unbalanced (resultant) force in newtons (N), m is mass in kilograms (kg) and a is acceleration in m/s². One newton is the force needed to accelerate 1 kg by 1 m/s².
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