📚 Year 7 OCR Science: Formulas & Principles Quick Reference Handbook | Year 7 OCR 科学：公式定理速查手册
Welcome to your Year 7 OCR Science quick reference guide. This handbook compiles the essential formulas, principles, and key concepts you will encounter across Physics, Chemistry, and Biology. Use it to reinforce your understanding and to check facts quickly while studying.
欢迎使用你的 Year 7 OCR 科学速查手册。本手册汇编了你将在物理、化学和生物学科中遇到的基本公式、定理和关键概念。在复习时使用它，可以巩固理解并快速核对知识点。
1. Speed, Distance and Time | 速度、距离和时间
Average speed tells you how fast something is moving. It is calculated by dividing the total distance travelled by the total time taken.
平均速度描述物体运动的快慢。它通过总行驶距离除以总时间来计算。
speed = distance ÷ time
速度 = 距离 ÷ 时间
The standard scientific units are metres per second (m/s) for speed, metres (m) for distance, and seconds (s) for time. You may also see speed given in kilometres per hour (km/h).
标准科学单位是：速度单位为米每秒 (m/s)，距离单位为米 (m)，时间单位为秒 (s)。你也可能看到速度以千米每小时 (km/h) 为单位。
On a distance–time graph, a straight, sloping line represents constant speed. The steeper the slope, the greater the speed.
在距离–时间图上，一条倾斜的直线代表匀速运动。斜率越大，速度越快。
2. Forces, Mass and Weight | 力、质量与重量
Weight is the force of gravity pulling on a mass. It is not the same as mass, which is the amount of matter in an object.
重量是重力对质量施加的拉力。它与质量不同，质量是物体所含物质的多少。
weight = mass × gravitational field strength
重量 = 质量 × 引力场强度
On Earth, gravitational field strength is approximately 10 N/kg. This means a 1 kg mass weighs 10 N. The formula is often written as W = m × g.
在地球上，引力场强度约为 10 N/kg。这意味着 1 kg 质量的物体重量为 10 N。该公式常写作 W = m × g。
Forces are measured in newtons (N) using a newton meter. Friction, air resistance, and upthrust are all examples of forces.
力以牛顿 (N) 为单位，使用牛顿计来测量。摩擦力、空气阻力和上推力都属于力。
3. Pressure, Area and Force | 压强、面积与力
Pressure describes how concentrated a force is over a surface. Spreading a force over a larger area reduces the pressure.
压强描述力在表面上的集中程度。把力分散到更大的面积上会减小压强。
pressure = force ÷ area
压强 = 力 ÷ 面积
The standard unit of pressure is the pascal (Pa), where 1 Pa = 1 N/m². A sharp knife exerts high pressure because the area of the cutting edge is very small.
压强的标准单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。锋利的刀因为刀刃面积非常小，所以能产生很大的压强。
In fluids, pressure increases with depth. Hydraulic systems use the principle that pressure is transmitted equally throughout a liquid.
在流体中，压强随深度增加而增大。液压系统利用压强在液体中均匀传递的原理工作。
4. Energy, Work and Power | 能量、功和功率
Work is done when a force moves an object. Energy is transferred as work, measured in joules (J).
当力使物体移动时就做了功。能量以功的形式转移，单位为焦耳 (J)。
work done = force × distance moved in the direction of the force
做功 = 力 × 沿力的方向移动的距离
Commonly written as W = F × d. Lifting a book upwards against gravity is an example of doing work.
通常写作 W = F × d。克服重力向上举起一本书就是做功的例子。
Power is the rate at which work is done or energy is transferred. The standard unit is the watt (W), where 1 W = 1 J/s.
功率是做功或能量转移的速率。标准单位是瓦特 (W)，1 W = 1 J/s。
power = work done ÷ time or power = energy transferred ÷ time
功率 = 做功 ÷ 时间 或 功率 = 能量转移量 ÷ 时间
5. Electrical Current, Voltage and Resistance | 电流、电压和电阻
Electric current is the flow of electric charge, measured in amperes (A). Voltage (potential difference) is the push that drives the current, measured in volts (V).
电流是电荷的流动，单位为安培 (A)。电压（电势差）是推动电流的“推力”，单位为伏特 (V)。
Resistance opposes the flow of current and is measured in ohms (Ω). Components like bulbs and resistors add resistance to a circuit.
电阻阻碍电流流动，单位为欧姆 (Ω)。灯泡和电阻器等元件会给电路增加电阻。
voltage = current × resistance
电压 = 电流 × 电阻
This is Ohm’s law, written as V = I × R. For a given resistor, if the voltage increases, the current increases proportionally.
这就是欧姆定律，写作 V = I × R。对于给定的电阻，如果电压升高，电流会按比例增大。
6. Density, Mass and Volume | 密度、质量与体积
Density tells you how much mass is packed into a certain volume. Objects with high density feel heavy for their size.
密度表示单位体积内包含的质量大小。密度大的物体在相同体积下会更重。
density = mass ÷ volume
密度 = 质量 ÷ 体积
The formula is often expressed as ρ = m ÷ V. Density can be measured in g/cm³ or kg/m³. Water has a density of 1 g/cm³.
公式常表示为 ρ = m ÷ V。密度的单位可以是 g/cm³ 或 kg/m³。水的密度为 1 g/cm³。
An object will float if its density is less than the density of the liquid it is placed in. This explains why ice floats on water.
如果物体的密度小于它所在液体的密度，它就会漂浮。这就解释了为什么冰能浮在水面上。
7. Particle Model and Changes of State | 粒子模型与状态变化
All substances are made of tiny particles. In solids, particles are closely packed in a regular pattern and vibrate in fixed positions.
所有物质都由微小粒子构成。固体中粒子紧密排列成规则图案，并在固定位置上振动。
In liquids, particles are close together but can move past each other. In gases, particles are far apart and move rapidly in all directions.
液体中粒子相互靠近但能彼此滑动。气体中粒子相距很远，并朝各个方向快速运动。
Changes of state include melting, freezing, boiling, condensing, and sublimation. Mass is conserved during these changes because the number of particles stays the same.
状态变化包括熔化、凝固、沸腾、冷凝和升华。这些变化中质量是守恒的，因为粒子总数保持不变。
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It is fastest in gases.
扩散是粒子从高浓度区域向低浓度区域运动的过程。它在气体中最快。
8. Chemical Reactions and Conservation of Mass | 化学反应与质量守恒
In a chemical reaction, the total mass of the reactants equals the total mass of the products. No atoms are created or destroyed.
在化学反应中，反应物的总质量等于生成物的总质量。原子既不会凭空产生，也不会被消灭。
total mass of reactants = total mass of products
反应物总质量 = 生成物总质量
This is the law of conservation of mass. It means we must balance chemical equations. For example, when hydrogen reacts with oxygen: 2H₂ + O₂ → 2H₂O.
这就是质量守恒定律。这意味着我们必须配平化学方程式。例如氢气与氧气反应：2H₂ + O₂ → 2H₂O。
State symbols in equations indicate whether a substance is solid (s), liquid (l), gas (g), or dissolved in water (aq).
方程式中的状态符号表示物质是固态 (s)、液态 (l)、气态 (g) 还是溶于水中的 (aq)。
9. Acids, Alkalis and the pH Scale | 酸、碱和 pH 标度
Acids have a pH less than 7, alkalis have a pH greater than 7, and a pH of 7 is neutral. The pH scale is a measure of the concentration of hydrogen ions.
酸的 pH 值小于 7，碱的 pH 值大于 7，pH 值为 7 时呈中性。pH 标度是氢离子浓度的量度。
Everyday acids include vinegar and lemon juice, while alkalis include soap and baking soda solution. Universal indicator turns red in strong acids and purple in strong alkalis.
日常生活中的酸有醋和柠檬汁，碱有肥皂和小苏打溶液。通用指示剂在强酸中变红，在强碱中变紫。
A neutralisation reaction occurs when an acid reacts with an alkali to form a salt and water. The general word equation is:
酸与碱反应生成盐和水，这称为中和反应。通用文字方程式为：
acid + alkali → salt + water
酸 + 碱 → 盐 + 水
For instance, hydrochloric acid reacting with sodium hydroxide produces sodium chloride and water: HCl + NaOH → NaCl + H₂O.
例如，盐酸与氢氧化钠反应生成氯化钠和水：HCl + NaOH → NaCl + H₂O。
10. Cells and Magnification | 细胞与放大倍数
All living organisms are made of cells. Animal cells contain a nucleus, cytoplasm, and cell membrane. Plant cells also have a cell wall, a large vacuole, and chloroplasts.
所有生物体都由细胞构成。动物细胞含有细胞核、细胞质和细胞膜。植物细胞此外还有细胞壁、大液泡和叶绿体。
Microscopes magnify tiny objects. The total magnification is found by multiplying the powers of the eyepiece and objective lenses.
显微镜能放大微小的物体。总放大倍数等于目镜倍数乘以物镜倍数。
total magnification = eyepiece magnification × objective magnification
总放大倍数 = 目镜放大倍数 × 物镜放大倍数
For example, using an eyepiece of ×10 and an objective of ×40 gives a total magnification of ×400. Always start focusing with the lowest power objective.
例如，使用 10× 目镜和 40× 物镜，总放大倍数为 400×。对焦时应始终从低倍物镜开始。
11. Photosynthesis and Respiration Equations | 光合作用与呼吸作用方程式
Photosynthesis is the process by which green plants make glucose using light energy, carbon dioxide, and water. Oxygen is released as a by-product.
光合作用是绿色植物利用光能、二氧化碳和水制造葡萄糖的过程，同时释放出氧气。
carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll)
二氧化碳 + 水 → 葡萄糖 + 氧气 （在光和叶绿素的作用下）
The balanced symbol equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This shows that six molecules of carbon dioxide and six molecules of water produce one molecule of glucose and six molecules of oxygen.
配平后的符号方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。这表明六分子二氧化碳和六分子水生成一分子葡萄糖和六分子氧气。
Aerobic respiration releases energy from glucose using oxygen. It occurs constantly in most living cells and can be summarised as:
有氧呼吸利用氧气从葡萄糖中释放能量。它在大多数活细胞中不断进行，可总结为：
glucose + oxygen → carbon dioxide + water (+ energy)
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 能量)
12. Ecological Pyramids and Energy Transfer | 生态金字塔与能量传递
A food chain shows the transfer of energy from producers (plants) to primary consumers, then to secondary consumers, and so on. Arrows point in the direction of energy flow.
食物链显示能量从生产者（植物）传递到初级消费者，再到次级消费者等。箭头指向能量流动的方向。
Energy pyramids represent the amount of energy at each trophic level. Typically, only about 10% of the energy is passed on to the next level; the rest is lost as heat, movement, or waste.
能量金字塔表示每个营养级的能量数量。通常只有大约 10% 的能量传递到下一个营养级，其余能量以热量、运动和废物的形式散失。
energy at next level ≈ 0.1 × energy at previous level
下一级能量 ≈ 0.1 × 上一级能量
This explains why food chains rarely have more than four or five trophic levels – there is simply not enough energy left to support another level.
这解释了为什么食物链很少超过四到五个营养级——留给更高层级的能量已经不足以支撑下一个级别。
Pyramids of number and biomass can also be used to describe ecosystems, but energy pyramids always show a decreasing pattern as you go up.
数量金字塔和生物量金字塔也可用于描述生态系统，但能量金字塔总是向上逐级缩小的。
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