📚 Year 7 CCEA Science: Quick-Reference Formula & Theorem Handbook | 七年级 CCEA 科学：公式定理速查手册
Welcome to your Year 7 CCEA Science formula and theorem quick-reference handbook. This guide brings together the essential equations, relationships, and scientific principles you will encounter during your first year of secondary science in Northern Ireland. Each section begins with a clear statement of the concept, followed by the mathematical expression where relevant, then practical examples to help you commit them to memory. Whether you are preparing for an end-of-topic test or revising for a larger assessment, use this handbook as your go-to summary for speed, density, forces, energy, electricity, particle theory, and more.
欢迎使用七年级 CCEA 科学公式定理速查手册。本指南汇集了你在北爱尔兰中学第一年科学课程中将遇到的核心方程式、数量关系和科学原理。每个小节先清晰陈述概念，接着在相关处给出数学表达式，然后通过实际例子帮助你牢记于心。无论你是在准备单元测验，还是为更大范围的评估复习，都可以把这份手册当作你查阅速度、密度、力、能量、电学、粒子理论等内容的快捷总结。
1. Speed, Distance and Time | 速度、距离和时间
The speed of an object tells you how quickly it is moving. It is the distance travelled in a certain amount of time. The formula triangle is very useful: cover the quantity you want, and the remaining two give the operation. If speed is constant, average speed equals total distance divided by total time.
物体的速度告诉你它移动的快慢程度。速度是单位时间内所通过的距离。公式三角形非常实用：遮住你想求的量，剩下的两个量就会提示该进行什么运算。如果速度恒定，则平均速度等于总距离除以总时间。
speed = distance ÷ time
s = d / t
For example, if a cyclist travels 300 metres in 25 seconds, the average speed is 300 m ÷ 25 s = 12 m/s. Always check the units: distance in metres (m), time in seconds (s), so speed is in metres per second (m/s). For longer journeys, you may use kilometres (km) and hours (h) to get km/h.
例如，如果一名骑行者 25 秒行驶了 300 米，平均速度为 300 m ÷ 25 s = 12 m/s。永远要检查单位：距离用米（m），时间用秒（s），因此速度的单位是米每秒（m/s）。对于较长的行程，你可以使用千米（km）和小时（h）来得到 km/h。
2. Density, Mass and Volume | 密度、质量和体积
Density describes how tightly packed the particles in a material are. A dense material, like lead, has a large mass for a small volume. The formula helps you compare materials and predict whether a substance will float or sink in water (density of water = 1 g/cm³).
密度描述了物质中粒子排列的紧密程度。密度大的物质，比如铅，在较小的体积内含有较大的质量。该公式帮助你比较不同材料，并预测某一物质在水中会浮起还是下沉（水的密度 = 1 g/cm³）。
density = mass ÷ volume
ρ = m / V
In the lab, you might measure mass in grams (g) with a balance and volume in cubic centimetres (cm³) using a measuring cylinder. The density then comes out in g/cm³. For instance, if a stone has a mass of 80 g and a volume of 20 cm³, its density is 80 ÷ 20 = 4 g/cm³.
在实验室中，你可能用天平称得质量（克，g），用量筒测出体积（立方厘米，cm³）。这样密度就以 g/cm³ 为单位。例如，若一块石块质量为 80 g，体积为 20 cm³，它的密度就是 80 ÷ 20 = 4 g/cm³。
3. Pressure, Force and Area | 压强、力和面积
Pressure measures how much force is applied over a given area. A small force over a tiny area can produce a high pressure (like the point of a drawing pin), while a large force spread over a big area gives low pressure (like a snowshoe on snow).
压强衡量作用在单位面积上的力的大小。很小的力作用在极小的面积上可以产生很大的压强（如图钉的尖端），而作用在大面积上的大力产生的压强反而小（如雪地里的雪鞋）。
pressure = force ÷ area
P = F / A
Force is measured in newtons (N), area in square metres (m²), so pressure is in pascals (Pa) or N/m². A book weighing 12 N lying flat on a table with an area of 0.2 m² exerts a pressure of 12 ÷ 0.2 = 60 Pa. If you stand that book on its narrow edge, the area decreases and the pressure increases – this explains why a sharp knife cuts more easily.
力以牛顿（N）为单位，面积以平方米（m²）为单位，因此压强单位是帕斯卡（Pa）或 N/m²。一本重 12 N 的书平放在桌面上，接触面积为 0.2 m²，产生的压强为 12 ÷ 0.2 = 60 Pa。如果让书竖起来用窄边接触桌面，面积减小，压强增大——这就解释了锋利的小刀为什么更容易切割。
4. Weight, Mass and Gravitational Field Strength | 重量、质量和重力场强度
On Earth, every object with mass experiences a force downwards due to gravity. This force is called weight. Mass is the amount of matter in an object and does not change from place to place, but weight depends on the gravitational field strength (g). On Earth, g is approximately 10 N/kg, so a 1 kg object weighs about 10 N.
在地球上，任何有质量的物体都会因重力而受到向下的力，这个力称为重量。质量是物体所含物质的多少，不会因地点的改变而变化，但重量取决于重力场强度（g）。在地球上，g 约等于 10 N/kg，因此一个 1 kg 的物体重量约为 10 N。
weight = mass × gravitational field strength
W = m × g
Remember not to confuse mass (measured in kilograms, kg) with weight (measured in newtons, N). An astronaut has the same mass on the Moon as on Earth, but their weight is only about one‑sixth because the Moon’s g is smaller. This equation helps design safe structures and understand everyday forces.
记住不要把质量（以千克 kg 为单位）与重量（以牛顿 N 为单位）混淆。一位宇航员在月球上的质量和在地球上相同，但他的重量只有地球上约六分之一，因为月球的重力场强度较小。这个方程式有助于设计安全的结构，并理解日常生活中的各种力。
5. Hooke’s Law and Extension of a Spring | 胡克定律与弹簧的伸长
When a spring is loaded with a force, it stretches. Hooke’s Law states that the extension (change in length) of the spring is directly proportional to the force applied, as long as the elastic limit is not exceeded. This linear relationship is fundamental in many measuring instruments.
当弹簧受到力的作用时，它会伸长。胡克定律指出，只要不超过弹性极限，弹簧的伸长量（长度的变化量）与所施加的力成正比。这种线性关系在许多测量仪器中都是基础。
force = spring constant × extension
F = k × e
Here, k is the spring constant (measured in N/m) and e is the extension in metres. If a spring with k = 50 N/m stretches by 0.1 m, the applied force is 50 × 0.1 = 5 N. Plotting a graph of force against extension gives a straight line through the origin – a hallmark of direct proportion.
其中，k 是弹簧常数（单位 N/m），e 是伸长量（单位米）。如果一个弹簧常数 k = 50 N/m 的弹簧伸长了 0.1 m，那么所施加的力为 50 × 0.1 = 5 N。以力对伸长量作图会得到一条过原点的直线——这是正比例的典型特征。
6. Conservation of Mass in Chemical Reactions | 化学反应中的质量守恒
During a chemical reaction, atoms rearrange to form new substances, but no atoms are created or destroyed. This is the law of conservation of mass: the total mass of the reactants equals the total mass of the products. In a closed system, you would observe no change in the reading on a balance.
在化学反应中，原子重新组合形成新物质，但原子不会被创造或毁灭。这就是质量守恒定律：反应物的总质量等于生成物的总质量。在一个封闭系统中，天平的读数不会发生变化。
For example, if you burn magnesium in a crucible with a lid, the magnesium oxide produced has a greater mass than the original magnesium because oxygen from the air has been added. The total mass of magnesium + oxygen gas equals the mass of magnesium oxide. We use word equations to represent this: magnesium + oxygen → magnesium oxide.
例如，在带盖的坩埚中燃烧镁条，生成的氧化镁比原来镁的质量更大，因为空气中的氧气参与了反应。镁 + 氧气的总质量等于氧化镁的质量。我们用文字方程式来表示：镁 + 氧气 → 氧化镁。
7. Ohm’s Law for Electric Circuits | 电路中的欧姆定律
Electric current (I) is the flow of charge, and voltage (V) is the push that drives it. Resistance (R) measures how difficult it is for the current to flow. Ohm’s Law links these three quantities in a simple proportion for many conductors, as long as temperature remains constant.
电流（I）是电荷的流动，电压（V）是推动电荷流动的“推力”。电阻（R）衡量电流流动的难易程度。对于许多导体，只要温度保持不变，欧姆定律就将这三个量用一个简单的比例关系联系起来。
voltage = current × resistance
V = I × R
Current is measured in amperes (A), voltage in volts (V), and resistance in ohms (Ω). If a lamp has a resistance of 10 Ω and is connected to a 5 V supply, the current drawn is 5 ÷ 10 = 0.5 A. The formula can be rearranged to I = V / R or R = V / I, depending on which quantity you need to find.
电流以安培（A）为单位，电压以伏特（V）为单位，电阻以欧姆（Ω）为单位。如果一盏灯的电阻为 10 Ω，接在 5 V 的电源上，流过它的电流为 5 ÷ 10 = 0.5 A。这个公式可以根据需要改写为 I = V / R 或 R = V / I，以求出不同的量。
8. Energy, Work and Power | 能量、功和功率
Energy is the ability to do work. Work is done when a force moves an object in the direction of the force. The amount of work is the product of the force and the distance moved. The unit of work and energy is the joule (J). Power tells you how fast work is done or energy is transferred.
能量是做功的能力。当一个力使物体沿力的方向移动时，就做了功。功的大小是力与移动距离的乘积。功和能量的单位都是焦耳（J）。功率则告诉你做功或能量转移的快慢。
work = force × distance
W = F × d
power = work ÷ time
P = W / t
If you lift a box weighing 100 N through a height of 2 m, the work done is 200 J. If you do this in 4 seconds, your power output is 200 ÷ 4 = 50 W (watts). These equations apply to any form of energy transfer, whether mechanical, electrical, or thermal.
如果你将一个重 100 N 的箱子提升 2 m，做功为 200 J。如果你在 4 秒内完成，你的输出功率为 200 ÷ 4 = 50 W（瓦特）。这些方程式适用于任何形式的能量转移，无论是机械能、电能还是热能。
9. Energy Efficiency | 能量效率
No energy transfer is perfectly useful; some energy is always spread to the surroundings, often as heat. Efficiency measures how much of the input energy is converted to useful output energy. A high efficiency means very little wasted energy.
没有哪种能量转换是完全有用的；总有一部分能量散失到周围环境中，通常以热的形式。效率衡量输入能量中有多少转化为有用的输出能量。效率高意味着浪费的能量很少。
efficiency = (useful output energy ÷ total input energy) × 100%
efficiency = (useful output power ÷ total input power) × 100%
For example, a light bulb that takes in 100 J of electrical energy and gives out 10 J of light and 90 J of heat has an efficiency of (10 ÷ 100) × 100% = 10%. Devices like LEDs have much higher efficiencies. Efficiency has no units because it is a ratio or a percentage.
例如，一只灯泡吸收 100 J 的电能，发出 10 J 的光能和 90 J 的热能，其效率为 (10 ÷ 100) × 100% = 10%。像 LED 这样的设备效率要高得多。效率没有单位，因为它是一个比值或百分比。
10. Particle Model and States of Matter | 粒子模型与物质状态
The particle model is a powerful idea that explains the properties of solids, liquids and gases. All matter is made of tiny particles that are constantly moving. In solids, particles vibrate in fixed positions; in liquids, they are in contact but can slide past one another; in gases, they move freely and are far apart.
粒子模型是一个很有力的观念，它解释了固体、液体和气体的性质。所有物质都由不断运动的微小粒子组成。在固体中，粒子在固定的位置上振动；在液体中，粒子相互接触但可以彼此滑动；在气体中，粒子自由运动且相距很远。
This model helps you understand density, compressibility and changes of state. When a solid is heated, particles vibrate more and can break away to form a liquid (melting). Further heating gives particles enough energy to escape as a gas (boiling). A change of state is a physical change, not a chemical one – the particles themselves do not alter.
这个模型帮助你理解密度、可压缩性以及状态变化。固体受热时，粒子振动加剧，能够挣脱束缚形成液体（熔化）。继续加热，粒子获得足够能量逃逸成为气体（沸腾）。状态的改变是物理变化，而不是化学变化——粒子本身没有改变。
11. Word Equations for Key Reactions | 关键反应的文字方程式
In Year 7, you learn to describe chemical reactions using word equations. A word equation shows the reactants on the left and the products on the right, linked by an arrow that means ‘change into’. Common reactions you should know include combustion, oxidation, and the reactions of acids with metals or carbonates.
在七年级，你学习用文字方程式描述化学反应。文字方程式左边是反应物，右边是生成物，中间用箭头连接，表示“变成”。你应该掌握常见反应，包括燃烧、氧化，以及酸与金属或碳酸盐的反应。
- Combustion of hydrogen: hydrogen + oxygen → water
- Combustion of hydrogen（氢的燃烧）: 氢气 + 氧气 → 水
- Oxidation of magnesium: magnesium + oxygen → magnesium oxide
- Oxidation of magnesium（镁的氧化）: 镁 + 氧气 → 氧化镁
- Acid and metal: metal + acid → salt + hydrogen
- Acid and metal（酸与金属）: 金属 + 酸 → 盐 + 氢气
- Acid and carbonate: carbonate + acid → salt + water + carbon dioxide
- Acid and carbonate（酸与碳酸盐）: 碳酸盐 + 酸 → 盐 + 水 + 二氧化碳
Learning to write balanced symbol equations will come later; for now, accurate word equations are a key skill for describing chemical changes.
学会书写配平的符号方程式是更高的要求；目前，能准确书写文字方程式是描述化学变化的关键技能。
12. Photosynthesis and Plant Nutrition | 光合作用与植物的营养
Plants make their own food through photosynthesis, a process that captures light energy to convert carbon dioxide and water into glucose and oxygen. This process happens in the chloroplasts of plant cells, which contain the green pigment chlorophyll.
植物通过光合作用制造自己的食物，这个过程捕获光能，将二氧化碳和水转化为葡萄糖和氧气。光合作用发生在植物细胞的叶绿体中，叶绿体含有绿色色素叶绿素。
carbon dioxide + water → glucose + oxygen
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (for information)
The glucose is used by the plant for energy and growth, and any extra is stored as starch. Remember that photosynthesis requires light, so it only occurs during the day. Plants provide the oxygen we breathe and are the foundation of most food chains.
葡萄糖被植物用于提供能量和生长，多余的则转化为淀粉储存起来。要记住，光合作用需要光，所以只在白天进行。植物提供了我们呼吸所需的氧气，也是大多数食物链的基础。
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