📚 Year 9 WJEC Science: Formula & Theorem Quick Reference Handbook | 九年级 WJEC 科学：公式定理速查手册
This handbook brings together the key formulas, equations and scientific theorems you will use in Year 9 WJEC Science. It covers physics, chemistry and biology, giving you a quick way to recall relationships, units and definitions as you practise problem-solving. Keep it with your revision notes and refer to it whenever you need a reminder.
本手册汇集了你在九年级 WJEC 科学课程中将用到的重要公式、方程式和科学定理。内容涵盖物理、化学和生物，帮助你在练习解题时快速回顾关系式、单位和定义。将它和你的复习笔记放在一起，需要时随时查阅。
1. Speed, Distance and Time | 速度、距离与时间
The most basic movement formula links speed, distance and time. Speed tells you how quickly distance is covered. You can rearrange the equation to find distance or time if you know the other two quantities.
最基本的运动公式将速度、距离和时间联系起来。速度表示覆盖距离的快慢。如果已知其他两个量，你可以将公式变形来求距离或时间。
speed = distance ÷ time
In symbols: v = d / t, where v is speed, d is distance and t is time. Units: if distance is in metres (m) and time in seconds (s), speed is in metres per second (m/s).
用符号表示：v = d / t，其中 v 代表速度，d 代表距离，t 代表时间。单位：若距离以米（m）为单位，时间以秒（s）为单位，则速度的单位是米每秒（m/s）。
. speed = 100 m ÷ 12.5 s = 8 m/s. The same formula works for average speed over a journey.
例如：一名短跑运动员在12.5秒内跑完100米。速度 = 100 m ÷ 12.5 s = 8 m/s。同样的公式也适用于一段行程中的平均速度。
2. Acceleration and Forces | 加速度与力
Acceleration is the rate at which velocity changes. It is calculated from the change in velocity divided by the time taken. When an object accelerates, a resultant force must be acting on it.
加速度是速度变化的快慢。它由速度变化量除以所用时间来计算。当物体加速时，一定是有合力作用在它身上。
a = (v – u) ÷ t
Here u is initial velocity, v is final velocity and t is the time for the change. The unit of acceleration is m/s² (metres per second squared).
其中 u 是初速度，v 是末速度，t 是变化所用的时间。加速度的单位是 m/s²（米每二次方秒）。
Newton's Second Law tells us the link between force, mass and acceleration. Weight is a particular force caused by gravity.
牛顿第二定律告诉我们力、质量和加速度之间的联系。重力是由引力引起的一种特殊的力。
F = m × a
W = m × g
m/s². Weight W is the force on a mass due to gravity; on Earth, g ≈ 10 N/kg (or 9.8 N/kg).
F 是合力，单位牛顿（N）；m 是质量，单位千克（kg）；a 是加速度，单位 m/s²。重力 W 是物体因引力受到的力；在地球上，g ≈ 10 N/kg（或 9.8 N/kg）。
3. Energy: Kinetic and Potential | 能量：动能与势能
Moving objects store kinetic energy. Objects raised above the ground store gravitational potential energy. Both are measured in joules (J).
运动的物体储存动能。被举离地面的物体储存重力势能。二者都以焦耳（J）为单位。
KE = ½ m v²
Kinetic energy = ½ × mass × (speed)². Doubling the speed quadruples the kinetic energy.
动能 = ½ × 质量 × 速度的平方。速度加倍会使动能变为原来的四倍。
GPE = m g h
energy = mass × gravitational field strength × height. h is the vertical height in metres.
重力势能 = 质量 × 重力场强 × 高度。h 是垂直高度，单位为米。
When an object falls with no air resistance, kinetic energy gained equals GPE lost – a useful application of energy conservation.
当物体在没有空气阻力的情况下下落时，获得的动能等于损失的重力势能——这是能量守恒的一个有用应用。
4. Work Done and Power | 功与功率
Work is done whenever a force moves an object. Energy transferred is equal to work done. Power describes how quickly work is done or energy is transferred.
只要力使物体移动，就做了功。转移的能量等于所做的功。功率描述做功或能量转移的快慢。
W = F × d
Work done (J) = force (N) × distance moved in the direction of the force (m).
所做的功（J）= 力（N）× 沿力的方向移动的距离（m）。
P = W ÷ t or P = E ÷ t
ork done (J) ÷ time (s) or energy transferred (J) ÷ time (s). 1 watt = 1 joule per second.
功率（W）= 功（J）÷ 时间（s）或 转移的能量（J）÷ 时间（s）。1瓦特 = 1焦耳每秒。
5. Electricity: Ohm's Law and Circuit Rules | 电学：欧姆定律与电路规则
Ohm's Law states that the current through a resistor is directly proportional to the potential difference across it, provided temperature remains constant.
欧姆定律指出，在温度保持不变的情况下，通过电阻的电流与其两端的电势差成正比。
V = I × R
Potential difference (V) in volts = current (A) × resistance (Ω). Rearranged: I = V / R, R = V / I.
电势差（V）单位伏特 = 电流（A）× 电阻（Ω）。可变形为：I = V / R，R = V / I。
Charge, energy and power in circuits are linked by further useful equations.
电路中的电荷、能量和功率通过以下实用公式相互关联。
Q = I × t
Charge (coulombs, C) = current (A) × time (s).
电荷（库仑，C）= 电流（A）× 时间（s）。
E = P × t and P = I × V
ransferred (J) = power (W) × time (s). Power (W) = current (A) × potential difference (V).
转移的能量（J）= 功率（W）× 时间（s）。功率（W）= 电流（A）× 电势差（V）。
Rules for series and parallel circuits are essential theorems:
串联和并联电路的规则是重要的定理：
- Series: current is the same everywhere; total voltage is shared; total resistance = R₁ + R₂ + …
- 串联：电流处处相等；总电压被分配；总电阻 = R₁ + R₂ + …
- Parallel: voltage is the same across each branch; total current splits between branches; total resistance is less than the smallest individual resistance.
- 并联：各支路两端电压相等；总电流在各支路间分流；总电阻小于最小的单个电阻。
6. Waves: Speed, Frequency and Wavelength | 波：波速、频率与波长
All waves obey the wave equation. It links wave speed, frequency and wavelength and is valid for sound, light and water waves.
所有波都遵循波动方程。它把波速、频率和波长联系在一起，适用于声波、光波和水波。
v = f × λ
wavelength λ (m). Frequency is the number of complete waves passing a point per second; wavelength is the distance between two corresponding points on adjacent waves.
波速 v（m/s）= 频率 f（Hz）× 波长 λ（m）。频率是每秒通过某点的完整波的个数；波长是相邻波的两个对应点之间的距离。
When a wave travels from one medium to another, its speed and wavelength may change, but its frequency stays the same. This theorem explains refraction.
当波从一种介质进入另一种介质时，波速和波长可能改变，但频率保持不变。这一定理解释了折射现象。
7. Density and Pressure | 密度与压强
Density describes how much mass is packed into a given volume. Pressure measures how concentrated a force is over an area.
密度描述单位体积内所含质量的大小。压强衡量力在面积上的集中程度。
ρ = m ÷ V
s (kg) ÷ volume (m³). ρ is the Greek letter rho. You can also use g/cm³ for small objects.
密度（kg/m³）= 质量（kg）÷ 体积（m³）。ρ 是希腊字母 rho。对于较小的物体也可使用 g/cm³。
p = F ÷ A
force (N) ÷ area (m²). A large pressure results from a large force acting on a small area – this principle explains why sharp blades cut easily.
压强（Pa 或 N/m²）= 力（N）÷ 面积（m²）。大力作用在小面积上会产生大压强——这一原理解释了为什么锋利的刀刃易于切割。
8. The Principle of Moments | 力矩原理
A moment is the turning effect of a force. It depends on the size of the force and how far it is applied from the pivot.
力矩是力的转动效应。它取决于力的大小以及力到支点的距离。
M = F × d
Moment (Nm) = force (N) × perpendicular distance from pivot (m).
力矩（Nm）= 力（N）× 到支点的垂直距离（m）。
Principle of moments: For a balanced lever or object in equilibrium, the total clockwise moment equals the total anticlockwise moment. This theorem is used to find unknown forces or distances in seesaws and cranes.
力矩原理：对于平衡的杠杆或处于平衡状态的物体，顺时针力矩之和等于逆时针力矩之和。这一定理可用于计算跷跷板或起重机中未知的力或距离。
9. Chemistry: Law of Conservation of Mass | 化学：质量守恒定律
A central theorem in chemistry is that mass is never created or destroyed in a chemical reaction. The total mass of reactants always equals the total mass of products.
化学的一个核心定理是：在化学反应中，质量既不会凭空产生，也不会凭空消失。反应物的总质量总是等于生成物的总质量。
This law explains why we must balance chemical equations. For example, when methane burns in oxygen, the number of atoms of each element stays the same on both sides:
这一定律解释了为什么我们必须配平化学方程式。例如，甲烷在氧气中燃烧时，每种元素的原子个数在两边保持不变：
CH₄ + 2O₂ → CO₂ + 2H₂O
, 4 hydrogen and 4 oxygen atoms appear on each side. Mass of reactants = mass of products.
数原子数：每边都有1个碳原子、4个氢原子和4个氧原子。反应物质量 = 生成物质量。
This theorem underpins all quantitative chemistry, including calculating reacting masses and yields.
这一定理是所有定量化学的基础，包括计算反应质量和产率。
10. Reactivity and General Reaction Patterns | 反应活性与常见反应规律
The reactivity series orders metals by how vigorously they react. It is an important tool for predicting displacement reactions and extraction methods.
金属活动性顺序根据金属反应的剧烈程度进行排列。它是预测置换反应和提取方法的重要工具。
metal from its compound. For example, magnesium + copper oxide → magnesium oxide + copper.
九年级中一个常见的定理是：较活泼的金属能把较不活泼的金属从其化合物中置换出来。例如，镁 + 氧化铜 → 氧化镁 + 铜。
General word equations for acid reactions are also like formula rules:
酸反应的通用文字方程式也类似于公式规则：
- metal + acid → salt + hydrogen
- 金属 + 酸 → 盐 + 氢气
- metal oxide + acid → salt + water
- 金属氧化物 + 酸 → 盐 + 水
- metal carbonate + acid → salt + water + carbon dioxide
- 金属碳酸盐 + 酸 → 盐 + 水 + 二氧化碳
Recognising these patterns lets you predict products in new reactions.
识别这些规律使你能够预测新反应的产物。
11. Biology: Microscopy and Magnification | 生物：显微镜与放大倍数
In biology, a key formula is the calculation of total magnification when using a light microscope. It allows you to work out how much larger a specimen appears.
在生物学中，一个关键公式是在使用光学显微镜时计算总放大倍数。它让你能算出标本被放大了多少倍。
total magnification = eyepiece magnification × objective magnification
ires using graticules and understanding the relationship between image size, actual size and magnification.
例如，10倍的目镜和40倍的物镜给出的总放大倍数为400倍。测量细胞时常需要使用测微尺，并理解图像尺寸、实际尺寸和放大倍数之间的关系。
e ÷ size of real object. This relationship is essential for drawing scale diagrams of cells.
尽管九年级不总以方程式呈现，其背后的定理是：放大倍数 = 图像尺寸 ÷ 实物尺寸。这一关系对绘制细胞的比例图至关重要。
12. Photosynthesis and Respiration Word Equations | 光合作用与呼吸作用文字方程式
Two fundamental biological processes can be summarised as word equations that behave like formulae, showing the inputs and outputs of energy and matter.
两个基本的生物学过程可以用文字方程式概括，它们像公式一样显示能量与物质的输入和输出。
Photosynthesis – the process plants use to make food using light energy:
光合作用——植物利用光能制造养分的过程：
carbon dioxide + water → glucose + oxygen
This reaction takes place in chloroplasts and requires light
Published by TutorHao | Year 9 Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图