📚 Year 7 WJEC Science: Quick Reference Handbook of Formulas and Principles | WJEC 7年级科学：公式定理速查手册
This reference handbook brings together the key formulas, equations and fundamental principles you will encounter in Year 7 WJEC Science. Whether you are preparing for an end-of-topic test or building your scientific vocabulary, these concise explanations will help you recall what each relationship means, how to use it and why it matters. Use it alongside your practical work and revision notes for a complete understanding.
这本速查手册汇集了你在 WJEC 7年级科学课程中会遇到的关键公式、方程式和基本原理。无论你是在准备单元测验，还是在积累科学词汇量，这些简明的解释都能帮你回顾每个关系式的含义、使用方法和重要性。请将它和你的实验记录、复习笔记一起使用，以达到全面理解。
1. Scientific Variables and SI Units | 科学变量与国际单位制
In any investigation, the independent variable is the one you change deliberately, the dependent variable is the one you measure as a result, and control variables are the ones you keep the same to ensure a fair test. Every measurement must include a unit based on the International System of Units (SI).
在任何探究实验中，自变量是你有意改变的变量，因变量是你观察测量的结果，控制变量则是你保持不变的量，以确保实验的公平性。每一个测量值都必须带有基于国际单位制（SI）的单位。
The seven base SI quantities include length (metre, m), mass (kilogram, kg), time (second, s), electric current (ampere, A), temperature (kelvin, K), amount of substance (mole, mol) and luminous intensity (candela, cd). In Year 7, you will mostly use derived units like metres per second (m/s), newtons (N) and pascals (Pa).
七个基本 SI 量分别是长度（米，m）、质量（千克，kg）、时间（秒，s）、电流（安培，A）、温度（开尔文，K）、物质的量（摩尔，mol）和发光强度（坎德拉，cd）。在7年级，你最常用的将是导出单位，如米每秒（m/s）、牛顿（N）和帕斯卡（Pa）。
A formula triangle can reorganise a three-variable equation. Cover the symbol you want to find and the triangle shows you whether to multiply or divide the other two.
公式三角形可以重组三个变量的方程。遮住你想求的符号，三角形就会提示你该对另外两个量进行乘法还是除法。
2. Speed | 速度
Speed describes how fast an object is moving without regard to direction. It is a scalar quantity. The average speed of an object is the total distance travelled divided by the total time taken.
速度描述物体运动的快慢，不考虑方向，是一种标量。物体的平均速度等于总运动距离除以总时间。
average speed = total distance ÷ total time
平均速度 = 总距离 ÷ 总时间
In symbols, this is often written as v = d ÷ t. The standard unit is metre per second (m/s), but you may also see kilometres per hour (km/h). To convert m/s to km/h, multiply by 3.6.
用符号表示常写作 v = d ÷ t。标准单位是米每秒（m/s），但你也可能看到千米每小时（km/h）。要将 m/s 转换为 km/h，乘 3.6 即可。
When an object moves at a steady speed in a straight line, the distance–time graph is a straight diagonal line. A steeper slope means a higher speed. A horizontal line represents a stationary object.
当物体沿直线匀速运动时，距离–时间图像是一条倾斜的直线。斜率越大代表速度越高。一条水平线则表示物体静止不动。
3. Density | 密度
Density is a measure of how much mass is packed into a given volume. It tells you whether a substance will float or sink in water: objects with a density less than 1 g/cm³ float, while those with a density greater than 1 g/cm³ sink.
密度衡量的是单位体积内所含质量的多少。它能告诉你物质在水中会浮起还是下沉：密度小于 1 g/cm³ 的物体会浮起，大于 1 g/cm³ 的则会下沉。
density = mass ÷ volume
密度 = 质量 ÷ 体积
ommon units are g/cm³ for solids and liquids, and kg/m³ for gases. Remember that the volume of a regular solid can be found by length × width × height; irregular solids need the displacement method.
符号形式为 ρ = m ÷ V。常见单位中，固体和液体用 g/cm³，气体用 kg/m³。记住，规则固体的体积可以用 长 × 宽 × 高 求得；不规则固体则需使用排水法。
Unlike mass, density does not depend on the size of the sample — it is a characteristic property of the material. A large iron nail and a tiny iron filing have the same density.
与质量不同，密度不取决于样本的大小——它是材料的一种特征属性。一枚大铁钉和一粒细小的铁屑具有相同的密度。
4. Pressure | 压强
Pressure tells us how concentrated a force is. The same force applied over a smaller area creates a larger pressure. This explains why sharp knives cut easily and why snow shoes prevent you from sinking into snow.
压强告诉我们力的集中程度。相同的力作用在更小的面积上会产生更大的压强。这就解释了为什么锋利的刀具容易切割，以及为什么雪地靴可以防止你陷入雪中。
pressure = force ÷ area
压强 = 力 ÷ 面积
ne pascal is a very small pressure; atmospheric pressure at sea level is about 100,000 Pa.
用符号表示为 P = F ÷ A。压强的 SI 单位是帕斯卡（Pa），1 Pa = 1 N/m²。1帕斯卡是非常小的压强；海平面大气压强约为 100,000 Pa。
In liquids, pressure increases with depth and acts equally in all directions. Hydraulic systems use this principle to multiply a force: a small force on a small piston can generate a large force on a larger piston because the pressure in the fluid is constant.
在液体中，压强随深度增加而增大，并且在各个方向上作用相等。液压系统利用这一原理来放大力：由于液体中压强处处相等，作用在小活塞上的小力可以在大活塞上产生大力。
5. Work Done and Energy Transfer | 做功与能量转移
When a force moves an object through a distance, work is done on the object and energy is transferred. The scientific definition of work is precise: a force must cause a displacement in the direction of the force.
当一个力推动物体移动一段距离时，就对物体做了功，能量发生了转移。功的科学定义十分精确：力必须在其作用方向上引起了位移。
work done = force × distance moved in the direction of the force
做功 = 力 × 沿力方向移动的距离
work is the joule (J); 1 J is the work done when a force of 1 N moves an object 1 m. If you push against a wall but it does not move, no scientific work is done, even though you feel tired.
符号形式为 W = F × d。功的单位是焦耳（J）；1 J 就是 1 N 的力使物体移动 1 m 所做的功。如果你推墙但墙纹丝不动，尽管你会感到疲劳，但在科学意义上并不算做功。
Work done equals the amount of energy transferred. This principle links mechanics with energy stores: lifting a book transfers energy to its gravitational potential store, while friction transfers energy to the thermal store of the surroundings.
做功等于转移的能量大小。这一原理将力学与能量储存联系在一起：提起书本是把能量转移到它的重力势能储存中，而摩擦力则是把能量转移到周围环境的热能储存里。
6. Electric Current and Charge | 电流与电荷
Electric current is the rate of flow of electric charge. In a metal wire, the charge is carried by moving electrons. The size of the current tells you how many charges pass a point in the circuit each second.
电流是电荷流动的速率。在金属导线中，电荷由移动的电子携带。电流的大小告诉你每秒钟有多少电荷通过电路中的某一位置。
charge = current × time
电荷 = 电流 × 时间
easured in coulombs (C), current in amperes (A) and time in seconds (s). So 1 coulomb is the charge that flows past a point in one second when the current is 1 ampere.
符号表示为 Q = I × t。电荷的单位是库仑（C），电流的单位是安培（A），时间的单位是秒（s）。因此，1 库仑就是 1 安培电流在 1 秒内通过某一点的电荷量。
In a series circuit, the current is the same at all points. In a parallel circuit, the current is shared between the branches, but the total current leaving the battery equals the sum of the branch currents.
在串联电路中，各处电流大小相等。在并联电路中，电流在各支路中分流，但离开电池的总电流等于各支路电流之和。
7. Voltage (Potential Difference) | 电压（电势差）
Voltage, also called potential difference, is a measure of the energy transferred to or from the charges as they move through a component. It acts like the 'push' that drives current around a circuit.
电压，也称为电势差，衡量的是电荷在通过某个元件时转移了多少能量。它就像是驱动电流在电路中流动的“推力”。
voltage = energy transferred ÷ charge
电压 = 转移的能量 ÷ 电荷
f voltage is the volt (V); 1 V means 1 joule of energy is transferred by each coulomb of charge. Batteries and power packs are labelled with their voltage, indicating how much energy they supply to each coulomb.
符号形式为 V = E ÷ Q。电压的单位是伏特（V）；1 V 表示每库仑电荷转移了 1 焦耳的能量。电池和电源上都标有电压值，表明它们能为每库仑电荷提供多少能量。
In a series circuit, the supply voltage is shared across the components. In a parallel circuit, each branch receives the full supply voltage.
在串联电路中，电源电压被各个元件分担。而在并联电路中，每个支路都获得完整的电源电压。
8. Microscope Magnification | 显微镜放大倍数
Light microscopes are used to observe cells and microorganisms. The total magnification is found by multiplying the power of the eyepiece lens by the power of the objective lens.
光学显微镜用于观察细胞和微生物。总放大倍数等于目镜放大倍数乘以物镜放大倍数。
total magnification = eyepiece magnification × objective magnification
总放大倍数 = 目镜放大倍数 × 物镜放大倍数
pecimen, use the formula: actual size = image size ÷ magnification. Always ensure both sizes are in the same unit.
例如，如果目镜是 ×10，物镜是 ×40，总放大倍数就是 ×400。要计算样本的实际大小，可使用公式：实际尺寸 = 图像尺寸 ÷ 放大倍数。务必确保两者的单位相同。
When you draw biological specimens, include a title, a scale bar and labels written in pencil. The magnification of your drawing can be found by dividing the drawn size by the actual size of the specimen.
当你绘制生物标本时，记得写上标题、比例尺，并用铅笔标注。你绘图时的放大倍数可以通过绘图尺寸除以样本实际尺寸求得。
9. Photosynthesis and Respiration Word Equations | 光合作用与呼吸作用文字方程
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesise nutrients from carbon dioxide and water. It produces glucose and releases oxygen as a by-product. The process takes place in chloroplasts containing chlorophyll.
光合作用是绿色植物和一些其他生物利用阳光，将二氧化碳和水合成营养物质的过程。它生成葡萄糖，并释放氧气作为副产物。该过程发生在含有叶绿素的叶绿体中。
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
Aerobic respiration is the chemical reaction that releases energy from glucose in the mitochondria of cells. It requires oxygen and produces carbon dioxide and water as waste products. The energy released is used for growth, repair and movement.
有氧呼吸是在细胞线粒体中从葡萄糖释放能量的化学反应。它需要氧气，并产生二氧化碳和水作为废物。释放的能量用于生长、修复和运动。
glucose + oxygen → carbon dioxide + water (+ energy)
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 能量)
Notice that aerobic respiration and photosynthesis are, in a sense, reverse processes. Respiration releases energy for cellular activities, while photosynthesis traps energy from sunlight into chemical stores.
可以注意到，有氧呼吸与光合作用在某种意义上互为逆过程。呼吸作用为细胞活动释放能量，而光合作用则将阳光中的能量捕获并储存在化学物质中。
10. States of Matter and the Particle Model | 物质状态与粒子模型
The particle model describes how the arrangement and movement of particles explain the properties of solids, liquids and gases. It is a powerful tool for predicting behaviour during changes of state.
粒子模型描述了粒子的排列和运动方式是如何解释固体、液体和气体的性质的。它是预测状态变化过程中物质行为的强有力工具。
In solids, particles are held tightly in a fixed, regular arrangement. They vibrate around fixed positions, giving solids a definite shape and volume. In liquids, particles are close together but can slide past one another, so a liquid has a fixed volume but takes the shape of its container. In gases, particles are far apart and move rapidly in all directions, so gases have no fixed shape or volume and can be compressed.
在固体中，粒子被紧密地固定在规则排列中，只能在固定位置振动，因而固体具有确定的形状和体积。在液体中，粒子紧密接触但可以相互滑过，因此液体具有固定的体积，但会随容器改变形状。在气体中，粒子相距很远，并向各个方向快速运动，因此气体没有固定的形状和体积，且可以被压缩。
When a substance changes state, the particles themselves do not change – only their arrangement and energy. During melting or boiling, energy is added to overcome forces between particles; during condensing or freezing, energy is removed.
当物质改变状态时，粒子本身并不改变——改变的只是它们的排列方式和能量。在熔化或沸腾过程中，需要加入能量来克服粒子间的吸引力；在凝结或凝固过程中，则要移走能量。
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It happens faster in gases than in liquids, and faster at higher temperatures because particles have more kinetic energy.
扩散是粒子从高浓度区域向低浓度区域运动的过程。在气体中的扩散比液体中快，在较高温度下也更快，因为粒子具有更大的动能。
11. The Cell Theory | 细胞学说
The cell theory is a fundamental concept in biology. It states three things: all living organisms are composed of one or more cells; the cell is the basic unit of structure and organisation in organisms; and all cells arise from pre-existing cells.
细胞学说是生物学中的一个基本概念。它阐述了三点：所有生物体都由一个或多个细胞组成；细胞是生物体结构和组织的基本单位；所有细胞都来源于已存在的细胞。
Plant and animal cells share several organelles: a nucleus that controls the cell and contains genetic material, cytoplasm where chemical reactions occur, a cell membrane that controls what enters and leaves, and mitochondria where respiration takes place. Plant cells also have a rigid cell wall made of cellulose, a large permanent vacuole filled with cell sap, and chloroplasts that absorb light for photosynthesis.
植物和动物细胞共有若干细胞器：控制细胞并含有遗传物质的细胞核，发生化学反应的细胞质，控制物质进出的细胞膜，以及进行呼吸作用的线粒体。植物细胞额外具有由纤维素构成的坚硬细胞壁、充满细胞液的大液泡，以及吸收光能进行光合作用的叶绿体。
Unicellular organisms, such as bacteria and amoeba, consist of a single cell that carries out all life processes. Multicellular organisms like humans have specialised cells — nerve cells, muscle cells, red blood cells — that work together in tissues, organs and organ systems.
单细胞生物，如细菌和变形虫，仅由一个细胞执行所有生命过程。像人类这样的多细胞生物则拥有特化的细胞——神经细胞、肌肉细胞、红细胞——它们共同形成组织、器官和器官系统。
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