📚 Year 8 CCEA Science: Quick Reference Handbook of Formulas and Laws | 八年级 CCEA 科学：公式定理速查手册
This quick reference handbook brings together the essential formulas, word equations and key laws you will encounter in Year 8 CCEA Science. From calculating speed and pressure to balancing chemical reactions and understanding photosynthesis, these summaries will help you revise efficiently and solve problems with confidence.
本速查手册汇集了八年级 CCEA 科学课程中的核心公式、文字方程式和关键定律。从计算速度和压强到配平化学反应和理解光合作用，这些总结将帮助你高效复习，自信解题。
1. Speed, Distance and Time | 速度、距离与时间
Speed tells you how fast an object is moving. Average speed is calculated by dividing the total distance travelled by the time taken.
速度表示物体运动的快慢。平均速度等于总路程除以总时间。
speed = distance / time or v = s / t
e (s = v × t) or time (t = s / v). To convert m/s into kilometres per hour (km/h), multiply by 3.6.
距离 (s) 的单位是米 (m)，时间 (t) 的单位是秒 (s)，速度 (v) 的单位是米每秒 (m/s)。你可以将公式变形来求距离 (s = v × t) 或时间 (t = s / v)。要将米每秒换算为千米每小时，乘以 3.6。
2. Acceleration | 加速度
Acceleration describes how quickly an object changes its velocity. It is found by dividing the change in velocity by the time taken for that change.
加速度描述物体速度变化的快慢。它等于速度的变化量除以发生这一变化所用的时间。
acceleration = change in velocity / time or a = (v - u) / t
Here, u is the initial velocity, v is the final velocity and t is the time. Acceleration is measured in metres per second squared (m/s²). If an object slows down, the acceleration is negative – we often call this deceleration.
其中 u 是初速度，v 是末速度，t 是时间。加速度的单位是米每二次方秒 (m/s²)。如果物体减速，加速度为负值，我们通常称之为减速度。
3. Weight, Mass and Gravity | 重量、质量与重力
Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity pulling on that mass. The weight of an object depends on the gravitational field strength, g.
质量是物体所含物质的多少，单位是千克 (kg)。重量是重力对物体的拉力。物体重量取决于引力场强度 g。
weight = mass × gravitational field strength or W = m × g
On Earth, g is about 9.8 N/kg, but you will often use 10 N/kg in calculations. Weight is a force, so it is measured in newtons (N).
在地球上，g 大约为 9.8 牛/千克，但计算中常用 10 牛/千克。重量是一种力，因此单位是牛顿 (N)。
4. Density | 密度
Density is a measure of how much mass is packed into a given volume. A dense material has a lot of mass in a small space.
密度是给定体积内所含质量的量度。密度大的材料在较小空间内含有较多质量。
density = mass / volume or ρ = m / V
Mass (m) is in kilograms (kg) or grams (g), volume (V) in cubic metres (m³) or cubic centimetres (cm³). Common units of density are kg/m³ and g/cm³. The density of water is 1 g/cm³.
质量 (m) 的单位为千克或克，体积 (V) 的单位为立方米或立方厘米。密度常用单位是 千克每立方米 和 克每立方厘米。水的密度是 1 克每立方厘米。
5. Pressure | 压强
Pressure tells you how concentrated a force is over an area. A small force over a tiny area can create a very high pressure.
压强表示力在面积上的集中程度。很小的力作用在很小的面积上可以产生很大的压强。
pressure = force / area or P = F / A
in pascals (Pa); 1 Pa = 1 N/m². Remember that for fluids pressure acts in all directions.
力 (F) 的单位是牛顿 (N)，面积 (A) 的单位是平方米 (m²)。压强的单位是帕斯卡 (Pa)，1 帕 = 1 牛/平方米。注意流体中的压强朝各个方向作用。
6. Moments | 力矩
A moment is the turning effect of a force. It depends on the size of the force and how far it is from the pivot.
力矩是力的转动效果。它取决于力的大小以及力到支点的距离。
moment = force × perpendicular distance from pivot or M = F × d
Force is measured in newtons (N) and distance in metres (m); moment is measured in newton-metres (Nm). For an object to be balanced, the total clockwise moment must equal the total anticlockwise moment.
力的单位是牛顿 (N)，距离的单位是米 (m)；力矩的单位是牛顿米 (Nm)。物体要平衡，总顺时针力矩必须等于总逆时针力矩。
7. Work, Energy and Power | 功、能量与功率
Work is done when a force moves an object. Energy is transferred and work done are both measured in joules (J).
当力使物体移动时就做了功。能量转移和做功都用焦耳 (J) 来衡量。
work done = force × distance or W = F × d
ial energy (GPE) gained by lifting an object is equal to m × g × h, where h is the height.
物体被举高而增加的重力势能等于 m × g × h，其中 h 是高度。
GPE = m g h
Power is the rate of doing work or transferring energy:
功率是做功或能量转移的速率：
power = work done / time or P = W / t
useful energy you get out: efficiency = (useful output energy / total input energy) × 100%.
功率的单位是瓦特 (W)，1 瓦 = 1 焦/秒。效率告诉你获得了多少有用的能量：效率 = (有用输出能量 / 总输入能量) × 100%。
8. Electrical Circuits and Ohm's Law | 电路与欧姆定律
Ohm's Law links voltage (potential difference), current and resistance in a circuit.
欧姆定律将电路中的电压、电流和电阻联系起来。
voltage = current × resistance or V = I × R
tage is shared and total resistance is the sum of individual resistances: Rₜₒₜₐₗ = R₁ + R₂ + ... In parallel circuits, voltage across each branch is equal, but current splits and total resistance decreases.
电压 (V) 的单位是伏特 (V)，电流 (I) 的单位是安培 (A)，电阻 (R) 的单位是欧姆 (Ω)。在串联电路中，电流处处相等，总电压被分压，总电阻等于各电阻之和：Rₜₒₜₐₗ = R₁ + R₂ + ... 在并联电路中，各支路电压相等，电流分流，总电阻减小。
9. Elements, Compounds and Chemical Symbols | 元素、化合物与化学符号
Every element is represented by a unique chemical symbol, usually one or two letters. A compound contains two or more different elements chemically joined together.
每种元素都有唯一的化学符号，通常为一或两个字母。化合物由两种或以上不同元素通过化学键结合而成。
| Element (Symbol) | 元素 (符号) |
| Hydrogen (H) | 氢 (H) |
| Carbon (C) | 碳 (C) |
| Oxygen (O) | 氧 (O) |
| Sodium (Na) | 钠 (Na) |
| Magnesium (Mg) | 镁 (Mg) |
| Chlorine (Cl) | 氯 (Cl) |
| Iron (Fe) | 铁 (Fe) |
| Copper (Cu) | 铜 (Cu) |
| Zinc (Zn) | 锌 (Zn) |
| Calcium (Ca) | 钙 (Ca) |
When writing a formula, use subscript numbers to show how many atoms of each element are in a molecule, e.g. H₂O, CO₂, CH₄.
书写化学式
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