Year 8 CAIE Science: Quick Reference Handbook of Formulas and Theorems | Year 8 CAIE 科学：公式定理速查手册

📚 Year 8 CAIE Science: Quick Reference Handbook of Formulas and Theorems | Year 8 CAIE 科学：公式定理速查手册

This handbook collects the essential formulas and core theorems for Year 8 CAIE Science. From speed calculations and circuit laws to chemical equations and biological processes, these concise summaries will help you revise quickly and build a strong foundation for higher-level study. Every key relationship is presented with clear symbols and practical context so you can apply them confidently in exams.

本手册汇总了 Year 8 CAIE 科学科目的核心公式与重要定理。无论是速度计算、电路定律，还是化学反应方程式与生物过程，这些简明扼要的总结将帮助你快速复习，为更高阶段的学习打下坚实基础。每个关键关系都用清晰的符号和实际情境呈现，让你在考试中运用自如。

1. Speed, Distance and Time | 速度、距离与时间

v = s / t

速度 = 距离 ÷ 时间，符号公式为 v = s / t。

The speed of an object tells us how much distance it covers in a certain time. The triangle formula speed = distance / time can be rearranged: distance = speed × time, time = distance ÷ speed. The standard unit of speed is metres per second (m/s), though kilometres per hour (km/h) is also common.

速度表示物体在单位时间内移动的距离。公式 速度 = 距离 ÷ 时间 可以变形为：距离 = 速度 × 时间，时间 = 距离 ÷ 速度。速度的标准单位是米每秒（m/s），千米每小时（km/h）也常被使用。

Average speed is total distance travelled divided by total time taken. If a car travels 100 km in 2 hours and then 50 km in 1 hour, its average speed is (100+50) km ÷ (2+1) h = 50 km/h. On a distance–time graph, a steeper slope means a higher speed; a horizontal line indicates the object is stationary.

平均速度等于总距离除以总时间。若一辆汽车2小时行驶100千米，再用1小时行驶50千米，则平均速度为（100+50）千米 ÷（2+1）小时 = 50千米/小时。在距离–时间图中，斜率越陡，速度越大；水平线表示物体静止。

To convert km/h to m/s, divide by 3.6. For example, 72 km/h = 72 ÷ 3.6 = 20 m/s. The conversion factor arises because 1 km = 1000 m and 1 h = 3600 s.

将千米/小时转换为米/秒，需除以3.6。例如72 km/h = 72 ÷ 3.6 = 20 m/s。转换因子来源于 1 km = 1000 m，1 h = 3600 s。

2. Acceleration | 加速度

a = (v – u) / t

加速度 =（末速度 – 初速度）÷ 时间，即 a = (v – u) / t。

Acceleration is the rate of change of velocity. It is a vector quantity, meaning it has both magnitude and direction. If the final speed v is greater than the initial speed u, the object accelerates; if v is smaller, it decelerates (negative acceleration). The SI unit is metres per second squared (m/s²).

加速度是速度的变化率。它是一个矢量，既有大小也有方向。如果末速度 v 大于初速度 u，物体加速；如果 v 小于 u，物体减速（负加速度）。国际单位是米每二次方秒（m/s²）。

A car increasing its speed from 5 m/s to 25 m/s in 4 seconds has an acceleration of (25 – 5) / 4 = 5 m/s². The same equation also works for uniform deceleration, where the value becomes negative.

一辆汽车在4秒内速度从5 m/s增加到25 m/s，其加速度为(25 – 5) / 4 = 5 m/s²。该公式同样适用于匀减速，此时加速度为负值。

3. Forces and Newton’s Laws | 力与牛顿定律

F = m a

力 = 质量 × 加速度，符号公式为 F = m a。

Newton’s First Law (Law of Inertia) states that an object remains at rest or moves with constant velocity unless acted upon by a resultant external force. Newton’s Second Law gives the relationship resultant force = mass × acceleration. The unit of force is the newton (N), where 1 N is the force needed to accelerate 1 kg by 1 m/s².

牛顿第一定律（惯性定律）指出，若物体不受外力作用，将保持静止或匀速直线运动状态。牛顿第二定律表达为 合力 = 质量 × 加速度。力的单位是牛顿（N），1 N 是使1 kg物体产生1 m/s²加速度所需的力。

Newton’s Third Law says that for every action there is an equal and opposite reaction. The weight of an object is the force due to gravity: W = m g, where g ≈ 9.8 N/kg on Earth (often rounded to 10 N/kg). Note that mass (kg) is a measure of the amount of matter, while weight (N) is a force.

牛顿第三定律指出，每一个作用力都有一个大小相等、方向相反的反作用力。物体的重量是重力导致的力：W = m g，地球上 g 约等于9.8 N/kg（常近似为10 N/kg）。注意质量（kg）是物体所含物质的量，而重量（N）是一种力。

4. Work, Energy and Power | 功、能与功率

W = F d

功 = 力 × 沿力方向移动的距离，即 W = F d。

Work is done when a force moves an object through a distance. One joule (J) is the work done when a force of 1 N moves an object 1 m in the direction of the force. Energy is the capacity to do work; kinetic energy is Eₖ = ½ m v² and gravitational potential energy is Eₚ = m g h. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted.

当力使物体沿力的方向移动一段距离时，我们就说力做了功。1焦耳（J）等于1 N的力使物体沿力方向移动1 m所做的功。能量是做功的本领；动能为 Eₖ = ½ m v²，重力势能为 Eₚ = m g h。能量守恒定律指出，能量既不能创生也不能消灭，只能转移或转化。

Power is the rate of doing work or transferring energy: P = W / t or P = E / t. The unit of power is the watt (W), where 1 W = 1 J/s. A machine that does 600 J of work in 5 seconds has a power of 120 W.

功率是做功或能量转移的速率：Published by TutorHao | Year 8 Science Revision Series | aleveler.com

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