📚 Year 8 WJEC Science: Quick-Reference Formula & Theorem Handbook | Year 8 WJEC 科学：公式定理速查手册
This handbook brings together the key formulas and theorems you will meet in Year 8 WJEC Science. From calculating speed and pressure to balancing chemical equations and understanding enzyme action, every principle is presented in clear, concise English–Chinese pairs. Use it alongside your lessons to check facts, revise for tests, and build confidence in the language of science.
本手册汇集了你在 Year 8 WJEC 科学课程中会遇到的核心公式和定理。从计算速度和压强，到配平化学方程式和理解酶的作用，每一个原理都以清晰简洁的英中对照形式呈现。结合课堂学习使用它，可以帮助你核查事实、备考复习，并建立对科学术语的信心。
1. Speed and Velocity Formulas | 速度与速率公式
Speed tells us how fast an object moves without considering direction. It is calculated by dividing the distance travelled by the time taken.
速度表示物体运动的快慢，不考虑方向。它通过物体移动的距离除以所用的时间来计算。
Speed = Distance ÷ Time
In symbols, this is often written as v = d / t, where v is speed, d is distance and t is time. The standard unit is metres per second (m/s), but kilometres per hour (km/h) is also common.
用符号表示常写作 v = d / t，其中 v 为速度，d 为距离，t 为时间。标准单位是米每秒 (m/s)，但千米每小时 (km/h) 也常用。
Velocity is simply speed in a stated direction. When motion is in a straight line, the magnitude of the velocity equals the speed, but you must still name the direction, e.g. 5 m/s north.
速率就是给定方向上的速度。当物体沿直线运动时，速率的大小等于速度，但你仍须指明方向，例如 5 m/s 向北。
2. Acceleration and Motion | 加速度与运动
Acceleration is the rate at which velocity changes. An object accelerates if it speeds up, slows down (decelerates) or changes direction.
加速度是速度变化的快慢。当物体加速、减速或改变方向时，它就具有加速度。
Acceleration = Change in Velocity ÷ Time Taken
Symbolically: a = (v – u) / t, where a is acceleration, v is final velocity, u is initial velocity and t is the time for the change. Acceleration is measured in metres per second squared (m/s²). If the value is negative, the object is decelerating.
符号公式：a = (v – u) / t，其中 a 为加速度，v 为末速度，u 为初速度，t 为变化的时间。加速度的单位是米每二次方秒 (m/s²)。若结果为负值，说明物体在减速。
On a velocity–time graph, acceleration is shown by the slope (gradient) of the line. A steeper slope means a larger acceleration. A horizontal line means constant velocity, and a downward slope means deceleration.
在速度–时间图上，加速度由线的斜率（梯度）表示。斜率越陡表示加速度越大。水平线表示匀速，向下倾斜的线表示减速。
3. Density, Mass, and Volume | 密度、质量与体积
Density describes how much mass is packed into a certain volume. It is a characteristic property of a material and does not depend on the size of the sample.
密度描述单位体积内含有多少质量。它是物质的一种特性，不随样本的大小而改变。
Density = Mass ÷ Volume
Written as ρ = m / V per cubic centimetre (g/cm³) is often used in the lab. Remember that 1 g/cm³ = 1000 kg/m³.
写作 ρ = m / V，其中 ρ 为密度，m 为质量，V 为体积。SI 单位是千克每立方米 (kg/m³)，但实验室也常用克每立方厘米 (g/cm³)。记住 1 g/cm³ = 1000 kg/m³。
If an object' explains why ice floats on water (density of ice ≈ 0.92 g/cm³) and why a steel nail sinks.
如果物体的密度小于它所放入的流体的密度，物体就会上浮；反之则下沉。这个原理解释了为什么冰能浮在水面上（冰的密度约 0.92 g/cm³），而钢钉会下沉。
4. Pressure, Force, and Area | 压强、力与面积
Pressure is the force applied perpendicular to a surface per unit area. Spreading a force over a larger area reduces the pressure.
压强是垂直作用于物体表面的力与受力面积之比。将力分散到更大的面积上会减小压强。
Pressure = Force ÷ Area
In symbols: P = F / A, where P is pressure (pascals, Pa), F is force (newtons, N) and A is area (square metres, m²). One pascal is equal to one newton per square metre.
符号公式：P = F / A，其中 P 为压强（帕斯卡，Pa），F 为力（牛顿，N），A 为面积（平方米，m²）。1 Pa 等于 1 N/m²。
High-heeled shoes create high pressure on the ground because the weight acts over a small area. Conversely, snowshoes reduce pressure by increasing the area in contact with the snow, preventing you from sinking.
高跟鞋会在地面产生高压强，是因为体重作用在很小的面积上。相反，雪鞋通过增大与雪地的接触面积来减小压强，防止下陷。
5. Work, Energy, and Power | 功、能与功率
Work is done whenever a force moves an object. Energy is the capacity to do work, and power is the rate at which work is done or energy is transferred.
当力使物体发生移动时，我们就说力做了功。能量是做功的能力，功率则是做功或能量转移的快慢。
Work Done = Force × Distance (in the direction of the force)
Formally, W = F × d, with work W in joules (J), force F in newtons (N) and distance d in metres (m). One joule is the work done when a force of one newton moves an object one metre.
公式为 W = F × d，其中功 W 的单位为焦耳 (J)，力 F 为牛顿 (N)，距离 d 为米 (m)。1 J 就是 1 N 的力使物体移动 1 m 所做的功。
Power = Work Done ÷ Time Taken, or Energy Transferred ÷ Time
Power P = W / t or P = E / t, measured in watts (W). One watt equals one joule per second. A 60 W light bulb transfers 60 J of electrical energy into light and heat every second.
功率 P = W / t 或 P = E / t，单位为瓦特 (W)。1 W 等于 1 J/s。一个 60 W 的灯泡每秒钟将 60 J 的电能转化为光能和热能。
6. Ohm's Law and Electrical Power | 欧姆定律与电功率
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.
欧姆定律指出，在温度不变的情况下，通过导体两点间的电流与这两点间的电压成正比。
Voltage = Current × Resistance
In symbols, V = I × R, where V is voltage (volts, V), I is current (amperes, A) and R is resistance (ohms, Ω). This relationship is fundamental to circuit analysis.
符号公式为 V = I × R，其中 V 为电压（伏特，V），I 为电流（安培，A），R 为电阻（欧姆，Ω）。这个关系是电路分析的基础。
Electrical power can be found from voltage and current: P = V × I, where P is power (watts, W). Combining with Ohm's Law, we also get P = I² × R and P = V² / R.
电功率也可以通过电压和电流计算：P = V × I，P 为功率（瓦特，W）。结合欧姆定律，还可以得到 P = I² × R 和 P = V² / R。
7. Wave Speed Equation | 波速方程
All waves, whether water waves, sound or light, follow the same basic equation linking speed, frequency and wavelength.
所有的波，无论是水波、声波还是光波，都遵循相同的基本方程，将速度、频率和波长联系在一起。
Wave Speed = Frequency × Wavelength
Written as v = f × λ, where v is wave speed (m/s), f is frequency (hertz, Hz) and λ (lambda) is wavelength (m). Frequency is the number of complete waves passing a point per second, while wavelength is the distance between two consecutive crests or compressions.
写作 v = f × λ，其中 v 为波速 (m/s)，f 为频率（赫兹，Hz），λ (lambda) 为波长 (m)。频率是每秒通过某点的完整波的数量，波长是两个相邻波峰或压缩区之间的距离。
When waves travel from one medium to another, their speed and wavelength change, but the frequency remains fixed. This is why a pencil looks bent when placed in a glass of water — light changes speed at the water–air boundary.
当波从一种介质进入另一种介质时，波速和波长会改变，但频率保持不变。这就是为什么铅笔放入水杯中看起来是弯的——光在水与空气的界面上速度发生了变化。
8. Conservation of Mass | 质量守恒定律
In a chemical reaction, atoms are neither created nor destroyed. The total mass of the reactants always equals the total mass of the products.
在化学反应中，原子既不会被创造也不会被消灭。反应物的总质量总是等于生成物的总质量。
This principle, first demonstrated by Antoine Lavoisier, means that chemical equations must be balanced. If you start with 12 g of carbon and 32 g of oxygen, you will end with exactly 44 g of carbon dioxide, assuming a complete reaction.
这个原理由拉瓦锡首次证明，意味着化学方程式必须配平。如果你从 12 g 碳和 32 g 氧气开始，完全反应后你将得到恰好 44 g 二氧化碳。
es. For example, the balanced equation for the combustion of methane is: CH₄ + 2O₂ → CO₂ + 2H₂O.
配平方程式时，只能调整系数（物质前面的大数字），绝不能改变化学式本身。例如，甲烷燃烧的配平方程式为：CH₄ + 2O₂ → CO₂ + 2H₂O。
9. Chemical Formulae and Equations | 化学式与方程式
A chemical formula shows the elements present in a compound and their relative numbers. Subscripts indicate how many atoms of each element are in one molecule or formula unit.
化学式表示化合物中含有哪些元素及其相对数量。下标表示一个分子或公式单元中每种元素的原子数。
| Substance | 物质 | Formula | 化学式 | Composition | 组成 |
|---|---|---|
| Water | 水 | H₂O | 2 hydrogen atoms, 1 oxygen atom | 2个氢原子，1个氧原子 |
| Carbon dioxide | 二氧化碳 | CO₂ | 1 carbon atom, 2 oxygen atoms | 1个碳原子，2个氧原子 |
| Glucose | 葡萄糖 | C₆H₁₂O₆ | 6 carbon, 12 hydrogen, 6 oxygen atoms | 6个碳原子，12个氢原子，6个氧原子 |
| Sodium chloride | 氯化钠 | NaCl | 1 sodium ion, 1 chloride ion | 1个钠离子，1个氯离子 |
n for photosynthesis is a key example in Year 8: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, catalysed by chlorophyll and light energy.
文字方程式使用反应物和生成物的名称，而符号方程式使用化学式，且必须始终配平。Year 8 的一个重要例子是光合作用的符号方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂，在叶绿素和光能催化下进行。
10. Photosynthesis and Respiration | 光合作用与呼吸作用
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesise nutrients from carbon dioxide and water. It stores energy in glucose.
光合作用是绿色植物和某些其他生物利用阳光，将二氧化碳和水合成为营养物质的过程。它把能量储存在葡萄糖中。
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The reaction requires chlorophyll and light. Oxygen is released as a by-product. The rate of photosynthesis is affected by light intensity, carbon dioxide concentration and temperature. At a certain point, one of these becomes the limiting factor that prevents a further increase in the rate.
该反应需要叶绿素和光。氧气作为副产物释放。光合作用的速率受光照强度、二氧化碳浓度和温度的影响。当其中一个因素达到极限时，它就会成为限制因子，阻止速率继续升高。
H₂O (+ energy in the form of ATP). This happens continuously in the mitochondria of living cells.
有氧呼吸是细胞在有氧条件下从葡萄糖中释放能量的过程。可概括为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O（+ 以 ATP 形式释放的能量）。这一过程在活细胞的线粒体中持续进行。
ts, it produces ethanol and carbon dioxide: glucose → ethanol + carbon dioxide (+ energy).
动物细胞和某些微生物的无氧呼吸产生乳酸和较少的能量：葡萄糖 → 乳酸（+ 能量）。在酵母和植物中，则产生乙醇和二氧化碳：葡萄糖 → 乙醇 + 二氧化碳（+ 能量）。
11. Enzyme Basics and Lock-and-Key Model | 酶基础与锁钥模型
Enzymes are biological catalysts made of protein. They speed up chemical reactions in living organisms without being used up or changed permanently.
酶是由蛋白质构成的生物催化剂。它们加速生物体内的化学反应，而自身不被消耗或永久改变。
The lock-and-key model describes enzyme action: the enzyme’s active site has a specific shape that is complementary to the shape of its substrate. The substrate fits into the active site like a key into a lock, forming an enzyme–substrate complex. The reaction then takes place, and the products are released, leaving the enzyme free to catalyse another reaction.
锁钥模型描述了酶的作用方式：酶的活性部位有特定的形状，与底物的形状互补。底物像钥匙插入锁孔一样进入活性部位，形成酶–底物复合物。随后发生反应，产物被释放，酶则可再次催化下一个反应。
Each enzyme works best at a particular temperature and pH. Extremes of temperature or pH can change the shape of the active site, a process called denaturation, so the substrate no longer fits. In humans, most enzymes have an optimum temperature near 37 °C.
每种酶都有其最适温度和最适 pH。极端的温度或 pH 会改变活性部位的形状，这个过程称为变性，导致底物无法再与之结合。在人体内，大多数酶的最适温度接近 37 °C。
Common examples include amylase (breaks down starch into maltose), protease (breaks proteins into amino acids) and lipase (breaks fats into fatty acids and glycerol). These enzymes are vital in digestion.
常见的例子有：淀粉酶（将淀粉分解为麦芽糖）、蛋白酶（将蛋白质分解为氨基酸）和脂肪酶（将脂肪分解为脂肪酸和甘油）。这些酶在消化过程中至关重要。
12. Genetic Principles: Mendel’s Laws | 遗传学原理：孟德尔定律
Genetics is the study of heredity. Gregor Mendel discovered basic patterns of inheritance by experimenting with pea plants. His ideas form the foundation of modern genetics.
遗传学是研究生物遗传的科学。孟德尔通过对豌豆植物的实验发现了遗传的基本模式。他的思想奠定了现代遗传学的基础。
The Law of Segregation states that each individual has two alleles for each gene, one inherited from each parent. During the formation of gametes (sex cells), these alleles separate so that each gamete carries only one allele for each gene.
分离定律指出，每个个体对于每个基因都有两个等位基因，分别遗传自父母双方。在配子（性细胞）形成过程中，这些等位基因分离，使得每个配子只携带每个基因的一个等位基因。
The Law of Independent Assortment states that alleles for different genes are distributed to gametes independently of one another, provided the genes are on different chromosomes. This leads to the huge variety seen in offspring.
自由组合定律指出，不同基因的等位基因独立地分配到配子中，只要这些基因位于不同的染色体上。这导致了后代中巨大的多样性。
Dominant alleles mask the effect of recessive alleles in heterozygous individuals. For example, in pea plants, the allele for tall stems (T) is dominant over the allele for short stems (t). A plant with genotype Tt will be tall. Only a plant with tt will be short.
显性等位基因在杂合个体中掩盖了隐性等位基因的效应。例如，在豌豆中，高茎等位基因 (T) 对矮茎等位基因 (t) 为显性。基因型为 Tt 的植株是高茎，只有 tt 植株才是矮茎。
itance of one gene. If two heterozygous parents (Tt × Tt) are crossed, the offspring have a 3:1 ratio of tall to short, because the genotypes are 1 TT : 2 Tt : 1 tt.
庞纳特方格用来预测杂交后代可能的基因型和表现型。单因子杂交考察一个基因的遗传。如果两个杂合亲本 (Tt × Tt) 杂交，后代高茎与矮茎的比例为 3:1，因为基因型比例为 1 TT : 2 Tt : 1 tt。
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