📚 Year 8 CCEA Science: Quick Reference Handbook of Formulas and Theorems | Year 8 CCEA 科学：公式定理速查手册
This handbook compiles the essential formulas and key theorems covered in the CCEA Year 8 Science curriculum. Use it as a quick reference for lesson reviews, homework help, and exam preparation. Every entry is presented in both English and Chinese to support bilingual learners at TutorHao.
本手册汇集了 CCEA Year 8 科学课程中的核心公式与重要定理，可作为课堂复习、作业辅导和考试准备的速查工具。每个条目均以英中双语呈现，助力 TutorHao 的双语学习者。
1. Speed and Motion | 速度与运动
Speed describes how fast an object moves. It is the distance travelled per unit of time. The formula to calculate average speed is:
速度描述物体运动的快慢，是单位时间内经过的路程。计算平均速度的公式为：
Speed = Distance ÷ Time
速度 = 路程 ÷ 时间
SI unit of speed is metres per second (m/s), but kilometres per hour (km/h) is also common.
用符号常写作 v = d / t。速度的国际单位是米每秒 (m/s)，但千米每小时 (km/h) 也常用。
2. Density and Buoyancy | 密度与浮力
Density measures how much mass is packed into a given volume. It helps explain why some objects float while others sink. The density formula is:
密度衡量一定体积内所含质量的多少，可用于解释为什么有的物体上浮、有的物体下沉。密度公式为：
Density = Mass ÷ Volume
密度 = 质量 ÷ 体积
Common units are grams per cubic centimetre (g/cm³) for solids and liquids, and kilograms per cubic metre (kg/m³) for gases. An object floats if its density is less than the density of the fluid it is placed in.
常用单位：固体和液体为克每立方厘米 (g/cm³)，气体为千克每立方米 (kg/m³)。当物体的密度小于所在流体的密度时，物体上浮。
3. Pressure in Fluids | 流体压强
Pressure is the force acting per unit area. It applies to both solids and fluids, but in liquids and gases the pressure acts in all directions. The pressure formula is:
压强是作用在单位面积上的力。固体和流体中都存在压强，但液体和气体中的压强向各个方向作用。压强公式为：
Pressure = Force ÷ Area
压强 = 力 ÷ 面积
rger force on a small area produces a high pressure, which is why sharp knives cut easily.
压强单位是帕斯卡 (Pa)，1 Pa = 1 N/m²;。在较小面积上施加较大的力会产生高压，这就是锋利的刀具容易切割的原因。
4. Moments and Levers | 力矩与杠杆
A moment is the turning effect of a force. It depends on the size of the force and the perpendicular distance from the pivot. The formula for the moment of a force is:
力矩是力的转动效应，它取决于力的大小和力到支点的垂直距离。力矩的计算公式为：
Moment = Force × Perpendicular distance from pivot
力矩 = 力 × 支点到力作用线的垂直距离
Moments are measured in newton metres (Nm). For a lever to balance, the total clockwise moment must equal the total anticlockwise moment. This is the principle of moments.
力矩的单位是牛顿米 (Nm)。杠杆平衡时，顺时针方向的总力矩等于逆时针方向的总力矩。这就是力矩原理。
5. Gravity and Weight | 重力与重量
Weight is the force of gravity acting on an object. It is directly proportional to the object's mass and the gravitational field strength. The relationship is expressed as:
重量是作用在物体上的重力，它与物体的质量以及重力场强度成正比。其关系式如下：
Weight = Mass × Gravitational field strength
重量 = 质量 × 重力场强度
th, g ≈ 10 N/kg, so a 1 kg mass weighs approximately 10 N. Weight is a force and is measured in newtons (N), while mass is measured in kilograms (kg).
通常写作 W = m × g。地球表面 g 约为 10 N/kg，因此 1 kg 的物体重量约为 10 N。重量是一种力，单位为牛顿 (N)；质量单位是千克 (kg)。
6. Work, Energy and Power | 功、能和功率
Work is done when a force moves an object. Energy is transferred during this process. The formula for work done is:
力使物体移动时即做了功，此过程中发生了能量转移。功的计算公式为：
Work done = Force × Distance moved in the direction of the force
做功 = 力 × 沿力方向移动的距离
Work and energy share the same unit, the joule (J). Power measures how quickly work is done. The power formula is:
功和能量具有相同的单位——焦耳 (J)。功率衡量做功的快慢，公式为：
Power = Work done ÷ Time taken
功率 = 做功 ÷ 所用时间
energy states that energy cannot be created or destroyed, only transferred or transformed.
功率单位是瓦特 (W)，1 W = 1 J/s。能量守恒定律指出，能量不能被创造或消灭，只能被转移或转化。
7. Ohm’s Law | 欧姆定律
For many conductors, the current flowing through a component is directly proportional to the voltage across it, provided the temperature remains constant. This relationship is known as Ohm’s Law:
对于许多导体，在温度保持不变的条件下，流过元件的电流与其两端的电压成正比。这个关系被称为欧姆定律：
Voltage = Current × Resistance
电压 = 电流 × 电阻
measured in volts (V), current in amperes (A), and resistance in ohms (Ω). Resistance tells us how difficult it is for current to flow.
符号表示为 V = I × R。电压单位为伏特 (V)，电流单位为安培 (A)，电阻单位为欧姆 (Ω)。电阻表示电流流动的难易程度。
8. Conservation of Mass | 质量守恒定律
During a chemical reaction, atoms are rearranged but no atoms are created or destroyed. Therefore, the total mass of the reactants always equals the total mass of the products. This is called the law of conservation of mass.
在化学反应中，原子重新组合，但原子既不会被创造也不会被消灭。因此，反应物的总质量总是等于生成物的总质量。这就是质量守恒定律。
For example, when magnesium burns in oxygen, the mass of magnesium oxide produced equals the combined mass of magnesium and oxygen that reacted. In a closed system, the mass before and after the reaction stays the same.
例如，镁在氧气中燃烧时，生成氧化镁的质量等于参加反应的镁和氧气的质量之和。在密闭体系中，反应前后的总质量保持不变。
9. Writing and Balancing Equations | 化学方程式的书写与配平
Chemical equations use symbols and formulas to show how reactants turn into products. A balanced equation has the same number of each type of atom on both sides. This reflects the conservation of mass.
化学方程式用符号和化学式表示反应物如何变为生成物。配平后的方程式左右两边各种原子的数目相等，这体现了质量守恒。
For example, the reaction between hydrogen and oxygen to form water is written as:
例如，氢气与氧气反应生成水的方程式为：
2H₂ + O₂ → 2H₂O
The coefficients (the numbers in front) ensure that there are four hydrogen atoms and two oxygen atoms on each side. Never change the small subscript numbers inside a formula to balance an equation.
前面的系数保证了等式两边各有 4 个氢原子和 2 个氧原子。切记，配平方程式时不能更改化学式中的小下标数字。
10. Photosynthesis Equation | 光合作用方程式
Photosynthesis is the process by which green plants use sunlight to make their own food. The overall word equation is:
光合作用是绿色植物利用阳光制造自身养分的过程，总文字方程式为：
Carbon dioxide + Water → Glucose + Oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
Sunlight energy is absorbed by chlorophyll in the chloroplasts. The balanced chemical equation, showing the number of molecules involved, is:
光能被叶绿体中的叶绿素吸收。配平后的化学方程式，显示了所涉及分子的数量：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
This reaction is endothermic – it takes in energy from its surroundings. It demonstrates how carbon dioxide and water are converted into glucose and oxygen, which are vital for life.
该反应是吸热反应，从周围环境吸收能量。它展示了二氧化碳和水如何转化为对生命至关重要的葡萄糖和氧气。
11. Aerobic Respiration | 有氧呼吸
Aerobic respiration is the process by which cells release energy from glucose using oxygen. It occurs continuously in the mitochondria of plant and animal cells. The word equation is:
有氧呼吸是细胞利用氧气从葡萄糖中释放能量的过程，在植物和动物细胞的线粒体中不断发生。文字方程式为：
Glucose + Oxygen → Carbon dioxide + Water (+ energy released)
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 释放的能量)
The balanced chemical equation is essentially the reverse of photosynthesis:
配平后的化学方程式基本上是光合作用的逆反应：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Respiration is exothermic; it transfers energy to the surroundings and provides the energy needed for processes like muscle contraction, growth and maintaining body temperature.
呼吸作用是放热反应，向周围环境释放能量，为肌肉收缩、生长和维持体温等生命活动提供必需的能量。
12. Cell Theory | 细胞学说
Cell theory is a fundamental concept in biology. It states that:
细胞学说是生物学的基本概念，包含以下要点：
- All living organisms are made up of one or more cells.
- 所有生物体都由一个或多个细胞组成。
- The cell is the basic unit of structure and function in living things.
- 细胞是生物体结构和功能的基本单位。
- All cells arise from pre-existing cells through cell division.
- 所有细胞都通过细胞分裂从已有细胞产生。
This theory unified our understanding of life and is supported by microscopic observations of cells such as plant cells (with cell wall, chloroplasts and large vacuole) and animal cells (with cell membrane, nucleus and cytoplasm).
该学说统一了对生命的认识，并得到了显微镜观察的支持，例如植物细胞（具有细胞壁、叶绿体和大液泡）和动物细胞（具有细胞膜、细胞核和细胞质）。
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