📚 KS3 AQA Science: Quick Reference Handbook of Formulas and Principles | KS3 AQA 科学：公式定理速查手册
Welcome to your one-stop quick reference for the most important formulas and principles in KS3 AQA Science. Whether you are revising physics, chemistry or biology, this handbook summarises the key equations, laws and word equations you need to master. Each entry is presented with clear definitions, units and real-world examples to build your confidence.
欢迎使用你的 KS3 AQA 科学一站式速查手册。无论你正在复习物理、化学还是生物，这本手册都汇集了必须掌握的核心公式、定律和文字方程式。每一条都配有清晰的定义、单位和贴近生活的例子，帮你轻松巩固理解。
1. Speed, Distance and Time | 速度、距离与时间
Speed describes how quickly an object is moving. It is calculated by dividing the distance travelled by the time taken.
速度描述物体运动的快慢，通过距离除以时间来计算。
speed = distance ÷ time
Speed is measured in metres per second (m/s) when distance is in metres (m) and time is in seconds (s). The formula can be rearranged to find distance (distance = speed × time) or time (time = distance ÷ speed).
当距离单位为米（m）、时间单位为秒（s）时，速度的单位是米每秒（m/s）。该公式可变形为求距离（距离 = 速度 × 时间）或求时间（时间 = 距离 ÷ 速度）。
For example, a cyclist who covers 300 m in 20 s has a speed of 300 ÷ 20 = 15 m/s.
例如，一名骑自行车的人在 20 s 内行驶 300 m，其速度为 300 ÷ 20 = 15 m/s。
2. Density | 密度
Density tells us how much mass is packed into a certain volume. It is found by dividing mass by volume.
密度表示单位体积内所含物质质量的多少，通过质量除以体积求得。
density = mass ÷ volume
Common units are kilograms per cubic metre (kg/m³) and grams per cubic centimetre (g/cm³). If an object's density is greater than that of water (1 g/cm³), it sinks; if it is less, it floats.
常用单位有千克每立方米（kg/m³）和克每立方厘米（g/cm³）。如果物体的密度大于水（1 g/cm³），它会下沉；小于水则会漂浮。
3. Pressure | 压强
Pressure is the amount of force acting on a unit area. The formula for pressure is:
压强是单位面积上受到的力的大小，计算公式为：
pressure = force ÷ area
Pressure is measured in pascals (Pa) when force is in newtons (N) and area is in square metres (m²). Increasing the area over which a force acts reduces the pressure — this is why snowshoes prevent you from sinking into soft snow.
当力的单位是牛顿（N）、面积的单位是平方米（m²）时，压强的单位是帕斯卡（Pa）。增大受力面积可以减小压强，这就是雪鞋能防止陷入松软雪地的原因。
4. Work Done and Energy Transfer | 做功与能量转移
Work is done whenever a force moves an object. The work done is equal to the energy transferred.
只要有力使物体移动，力就做了功。所做的功等于转移的能量。
work done = force × distance
Work done is measured in joules (J), force in newtons (N) and distance in metres (m). Lifting a 5 N book onto a shelf 2 m high requires 5 × 2 = 10 J of work.
功的单位是焦耳（J），力的单位是牛顿（N），距离的单位是米（m）。将一本重 5 N 的书抬起 2 m 放到书架上，需要做功 5 × 2 = 10 J。
5. Gravitational Potential Energy (GPE) | 重力势能
An object lifted above the ground stores gravitational potential energy. The formula is:
物体被举高后储存了重力势能，公式为：
GPE = mass × gravitational field strength × height
On Earth, the gravitational field strength (g) is approximately 10 N/kg. Mass is in kilograms (kg), height in metres (m), and GPE in joules (J). If you lift a 2 kg cat onto a 1.5 m wall, the GPE gained is 2 × 10 × 1.5 = 30 J.
在地球表面，引力场强度（g）约为 10 N/kg。质量的单位是千克（kg），高度的单位是米（m），重力势能的单位是焦耳（J）。将一只 2 kg 的猫抱上 1.5 m 高的墙，增加的重力势能为 2 × 10 × 1.5 = 30 J。
6. Hooke's Law | 胡克定律
Hooke's Law describes how springs stretch under force. It states that the extension of a spring is directly proportional to the force applied, provided the elastic limit is not exceeded.
胡克定律描述了弹簧受力拉伸的规律：在弹性限度内，弹簧的伸长量与所施加的力成正比。
force = spring constant × extension
Force is measured in newtons (N), the spring constant (k) in newtons per metre (N/m) and extension in metres (m). A stiff spring has a large spring constant; a stretchy spring has a small one.
力的单位是牛顿（N），弹簧常数（k）的单位是牛每米（N/m），伸长量的单位是米（m）。硬弹簧的弹簧常数大，软弹簧的弹簧常数小。
7. Ohm's Law | 欧姆定律
Ohm's Law links voltage, current and resistance in an electrical circuit. At constant temperature, the current through a resistor is directly proportional to the potential difference across it.
欧姆定律展现了电路中电压、电流和电阻的关系。温度不变时，流过电阻的电流与电阻两端的电压成正比。
voltage = current × resistance
Voltage (V) is measured in volts (V), current (I) in amperes (A) and resistance (R) in ohms (Ω). The formula can be rearranged as I = V ÷ R or R = V ÷ I.
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）。该公式可以变形为 I = V ÷ R 或 R = V ÷ I。
8. Conservation of Mass in Reactions | 化学反应中的质量守恒
In a chemical reaction, no atoms are created or destroyed. The total mass of the reactants therefore equals the total mass of the products.
在化学反应中，原子不被创造也不会消失。因此，反应物的总质量等于生成物的总质量。
total mass of reactants = total mass of products
For example, when 12 g of magnesium burns in air, it combines with oxygen to produce 20 g of magnesium oxide. The mass of oxygen used must be 8 g, showing that the total mass before and after the reaction is unchanged.
例如，12 g 镁在空气中燃烧，与氧气结合生成 20 g 氧化镁。根据质量守恒可知，参与反应的氧气质量为 8 g，反应前后总质量保持不变。
9. Photosynthesis Word Equation | 光合作用文字方程式
Green plants and algae use light energy to make their own food. The process of photosynthesis can be summarised in a word equation.
绿色植物和藻类利用光能自己制造食物，光合作用的过程可用文字方程式概括。
carbon dioxide + water → glucose + oxygen
This reaction takes place in the chloroplasts, requires light energy and chlorophyll, and converts light energy into chemical energy stored in glucose.
该反应在叶绿体中进行，需要光能和叶绿素，并将光能转化为储存在葡萄糖中的化学能。
10. Aerobic Respiration Word Equation | 有氧呼吸文字方程式
Aerobic respiration is the process cells use to release energy from glucose, using oxygen. The word equation is the reverse of photosynthesis.
有氧呼吸是细胞利用氧气从葡萄糖中释放能量的过程，其文字方程式正好与光合作用相反。
glucose + oxygen → carbon dioxide + water
This reaction takes place continuously in the mitochondria of living cells, releasing energy that is used for movement, growth and keeping warm.
该反应在活细胞的线粒体中持续进行，释放的能量用于运动、生长和保持体温。
11. Neutralisation Reaction | 中和反应
When an acid reacts with a base, a neutralisation reaction occurs, producing a salt and water. The general word equation is:
酸与碱发生中和反应，生成盐和水。通用的文字方程式为：
acid + base → salt + water
For instance, hydrochloric acid neutralises sodium hydroxide to form sodium chloride and water: hydrochloric acid + sodium hydroxide → sodium chloride + water. This is a key reaction used to control pH.
例如，盐酸与氢氧化钠中和生成氯化钠和水：盐酸 + 氢氧化钠 → 氯化钠 + 水。这是控制 pH 的重要反应。
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