📚 Year 8 SQA Science: Quick Reference Handbook of Formulas and Theorems | SQA 八年级科学：公式定理速查手册
This handbook brings together the essential formulas and scientific theorems you will encounter in Year 8 SQA Science. Use it to revise key ideas, practise rearranging equations, and check the correct units. Every topic is explained with worked examples so you can apply your knowledge confidently in assessments and practical work.
本手册汇集了八年级 SQA 科学课程中的核心公式与科学定理。你可以用它来复习关键概念、练习公式变形，并核对正确的单位。每个主题都配有解释和实例，帮助你在评估与实验操作中自信地运用所学知识。
1. Speed, Distance and Time | 速度、距离与时间
Speed tells us how quickly an object moves. The relationship between speed, distance and time is one of the most important formulas in physics. When an object moves at a constant speed, you can calculate any of the three quantities if you know the other two.
速度告诉我们物体移动的快慢。速度、距离与时间之间的关系是物理学中最重要的公式之一。当物体匀速运动时，只要知道其中两个量，就能算出第三个。
v = d ÷ t
In this equation, v stands for speed, d for distance travelled and t for the time taken. Speed is often measured in metres per second (m/s) or kilometres per hour (km/h). Distance is given in metres (m) or kilometres (km), and time in seconds (s) or hours (h). Always make sure units match before you substitute numbers.
在这个等式中，v 代表速度，d 代表移动距离，t 代表所用时间。速度通常以米每秒（m/s）或千米每小时（km/h）为单位。距离以米（m）或千米（km）为单位，时间以秒（s）或小时（h）为单位。代入数值前，务必确保单位一致。
find time, use t = d ÷ v. Memorising the formula triangle can help you rearrange quickly.
如果一名自行车手在 20 秒内骑行了 300 米，她的速度就是 v = 300 m ÷ 20 s = 15 m/s。求距离时可将公式变形为 d = v × t，求时间则用 t = d ÷ v。记住公式三角形有助于你快速进行变形。
2. Acceleration | 加速度
Acceleration measures how quickly the velocity of an object changes. An object accelerates if it speeds up, slows down (deceleration) or changes direction. The formula links initial velocity, final velocity and time.
加速度衡量物体速度变化的快慢。物体加速、减速（负加速度）或改变方向时都存在加速度。该公式将初速度、末时间和时间联系在一起。
a = (v - u) ÷ t
Here, a is acceleration, v is the final velocity, u is the initial velocity, and t is the time taken for the change. Acceleration is measured in metres per second squared (m/s²). If the value is negative, the object is decelerating.
此处 a 表示加速度，v 是末速度，u 是初速度，t 是变化所用时间。加速度的单位是米每二次方秒（m/s²）。如果计算结果为负，说明物体在减速。
25 - 5) ÷ 4 = 5 m/s². Remember: this formula only works for constant acceleration. For non‑uniform acceleration, you need more advanced tools.
一辆车在 4 秒内从 5 m/s 加速到 25 m/s，加速度 a = (25 - 5) ÷ 4 = 5 m/s²。注意：该公式仅适用于匀加速运动。变加速运动需要更高级的处理方法。
3. Newton's Second Law | 牛顿第二定律
Newton's Second Law explains the link between the force acting on an object, its mass, and the acceleration it experiences. It is one of the most powerful theorems in physics and underpins everything from vehicle safety to rocket launches.
牛顿第二定律解释了作用在物体上的力、物体质量及加速度之间的关系。它是物理学中最强大的定理之一，支撑着从汽车安全到火箭发射的所有内容。
F = m × a
Unbalanced force (F) is measured in newtons (N), mass (m) in kilograms (kg), and acceleration (a) in metres per second squared (m/s²). The direction of the acceleration is always the same as the direction of the resultant force.
非平衡力（F）的单位是牛顿（N），质量（m）单位为千克（kg），加速度（a）单位是米每二次方秒（m/s²）。加速度的方向始终与合外力的方向相同。
. This theorem is fundamental for understanding how objects move when forces are not balanced.
如果一辆 2 千克的玩具车以 3 m/s² 加速，作用在它上面的合力就是 F = 2 × 3 = 6 N。质量可通过 m = F ÷ a 求得，加速度则用 a = F ÷ m。该定理对于理解力不平衡时物体如何运动至关重要。
4. Weight and Mass | 重量与质量
Many students confuse weight and mass. Mass is the amount of matter in an object and does not change. Weight is the force of gravity acting on that mass. Your weight would be different on the Moon, but your mass would stay the same.
许多学生容易混淆重量和质量。质量是物体所含物质的多少，不会改变。重量则是作用在该质量上的重力。你在月球上的重量会不同，但质量保持不变。
W = m × g
W stands for weight in newtons (N), m is mass in kilograms (kg), and g is the gravitational field strength. On Earth, g is approximately 9.8 N/kg, but for many Year 8 calculations you may use 10 N/kg to keep things simple.
W 代表重量，单位为牛顿（N），m 是质量，单位为千克（kg），g 是引力场强度。在地球上，g 约等于 9.8 N/kg，但在许多八年级计算中，为简化起见可使用 10 N/kg。
mber to distinguish between mass (kg) and weight (N). The formula also helps you find the mass of an object if its weight is known.
一本质量为 1.5 千克的课本在地球上的重量为 W = 1.5 × 10 = 15 N。请始终区分质量（kg）和重量（N）。该公式也可用于根据已知重量求出物体质量。
5. Work, Energy and Power | 功、能量与功率
Work is done when a force moves an object through a distance. Energy is transferred. Power tells us the rate at which work is done or energy is transferred. These ideas connect directly to real‑world contexts like climbing stairs or lifting weights.
当一个力使物体移动一段距离时，就做了功。能量被转移。功率则告诉我们做功或转移能量的快慢。这些概念直接与爬楼梯或举重等真实情境相关联。
Work: W = F × d
Work done (W) is measured in joules (J), force (F) in newtons (N), and distance (d) moved in the direction of the force in metres (m). No work is done if there is no movement, no matter how large the force.
做功（W）的单位是焦耳（J），力（F）的单位是牛顿（N），沿力的方向移动的距离（d）的单位是米（m）。如果没有发生位移，无论力有多大都不做功。
Power: P = E ÷ t
nds (s). A lamp that transfers 300 J of energy in 15 s has a power of P = 300 ÷ 15 = 20 W.
功率（P）的单位是瓦特（W）。1 瓦特等于每秒转移 1 焦耳的能量。能量（E）的单位是焦耳（J），时间（t）的单位是秒（s）。一盏灯在 15 秒内转移 300 J 的能量，其功率为 P = 300 ÷ 15 = 20 W。
- If a force of 40 N pushes a box 5 m, work done = 40 × 5 = 200 J.
- 若用 40 N 的力推动箱子移动 5 m，做功为 40 × 5 = 200 J。
- When you run upstairs, your power output increases because the same work is done in less time.
- 当你跑上楼梯时，由于在更短时间内完成同样的功，你的输出功率会增加。
6. Electrical Power and Energy | 电功率与电能
Electrical appliances transfer energy. The rate of transfer is electrical power, which depends on current and voltage. You can also calculate the total energy transferred over a period of time.
用电器会转移能量。转移的速率就是电功率，取决于电流和电压。你还可以计算一段时间内转移的总能量。
P = I × V
Electrical power (P) is in watts (W), current (I) in amperes (A), and potential difference (V) in volts (V). This formula helps you understand why high‑voltage devices or those drawing a large current are more powerful.
电功率（P）的单位是瓦特（W），电流（I）的单位是安培（A），电势差（V）的单位是伏特（V）。该公式有助于理解为什么高电压或大电流的用电器功率更高。
E = P × t
multiplied by time in seconds. For mains electricity, energy is often measured in kilowatt‑ y (kWh) = Power (kW) × Time (h). A 2 kW heater used for 3 hours transfers 6 kWh of energy.
转移的能量（E）以焦耳为单位，等于功率乘以时间（秒）。对于市电，能量常用千瓦时（kWh）衡量：能量（kWh）= 功率（kW）× 时间（h）。一个 2 kW 的取暖器使用 3 小时，转移 6 kWh 能量。
7. Ohm's Law | 欧姆定律
Ohm's Law describes the relationship between voltage, current and resistance in a circuit at constant temperature. It is essential for designing circuits and choosing suitable components.
欧姆定律描述了恒温条件下电路中电压、电流与电阻之间的关系。这对设计电路和选择合适的元件至关重要。
R = V ÷ I
Resistance (R) is measured in ohms (Ω), potential difference (V) in volts (V), and current (I) in amperes (A). A component has a resistance of 1 Ω if a voltage of 1 V drives a current of 1 A through it.
电阻（R）的单位是欧姆（Ω），电势差（V）的单位是伏特（V），电流（I）的单位是安培（A）。若 1 V 电压驱动 1 A 电流通过某一元件，该元件的电阻就是 1 Ω。
To calculate current, rearrange the law: I = V ÷ R. To find voltage, use V = I × R. Ohm' ment bulb, the resistance increases with temperature, so the graph is not a straight line.
要计算电流，可将定律变形：I = V ÷ R；求电压则用 V = I × R。欧姆定律仅适用于温度恒定的欧姆导体。对于白炽灯泡，电阻随温度升高而增大，因此图像不是直线。
8. Density | 密度
Density tells us how much mass is packed into a given volume. It explains why some objects float and others sink, and it links to particle theory in chemistry.
密度表示单位体积内所含的质量。它解释了为何有些物体会浮起而另一些会下沉，并与化学中的粒子理论相联系。
ρ = m ÷ V
The Greek letter ρ stands for density. Its units are kilograms per metre cubed (kg/m³) or grams per centimetre cubed (g/cm³). Mass (m) is in kg or g, and volume (V) in m³ or cm³.
希腊字母 ρ 代表密度。其单位是千克每立方米（kg/m³）或克每立方厘米（g/cm³）。质量（m）的单位是 kg 或 g，体积（V）的单位是 m³ 或 cm³。
find the volume of a regular solid, use V = l × w × h before applying the density formula.
水的密度约为 1 g/cm³。密度小于 1 g/cm³ 的物体会浮在水上；密度大于该值的则下沉。对于规则固体，先利用 V = 长 × 宽 × 高 计算体积，再代入密度公式。
| Quantity 量 | Symbol 符号 | SI Unit 国际单位 |
| Density 密度 | ρ | kg/m³ |
| Mass 质量 | m | kg |
| Volume 体积 | V | m³ |
9. Chemical Reactions: Conservation of Mass | 化学反应：质量守恒
During a chemical reaction, atoms are rearranged but none are created or destroyed. This is the law of conservation of mass. It means the total mass of reactants equals the total mass of products in a closed system.
在化学反应中，原子重新排列，但没有原子被创造或消灭。这就是质量守恒定律。它意味着在封闭系统中，反应物的总质量等于生成物的总质量。
The theorem can be expressed as: Total mass of reactants = Total mass of products. This is why chemical equations must be balanced. When you burn magnesium in air, the mass of magnesium oxide produced appears to increase — but that is because oxygen from the air has combined with the magnesium. If you trap the oxygen, the total mass stays the same.
该定理可表达为：反应物的总质量 = 生成物的总质量。这就是为什么化学方程式必须配平。当你在空气中燃烧镁时，生成的氧化镁质量似乎增加了——但这是因为空气中的氧与镁发生了结合。如果将氧限制起来，总质量就会保持不变。
Example: 2Mg + O₂ → 2MgO
Using relative atomic masses, you can check that the number of each type of atom is the same on both sides. This conservation theorem helps chemists predict how much product will form in a reaction.
利用相对原子质量，你可以检查每种原子的数量在两边是否相等。该守恒定理帮助化学家预测反应中会生成多少产物。
10. Concentration of Solutions | 溶液浓度
Concentration tells you how much solute is dissolved in a certain volume of solvent. In Year 8, it is often calculated as mass per unit volume, which is useful for preparing solutions in experiments.
浓度告诉你一定体积溶剂中溶解了多少溶质。在八年级，通常以单位体积的质量来计算，这对实验中的溶液配制很有用。
Concentration = Mass of solute ÷ Volume of solvent
tration is 20 g / 0.5 L = 40 g/L. Always convert volumes to the same unit before dividing.
可写作单位 g/L 或 g/cm³。若将 20 g 食盐溶解在 500 cm³ 水中，浓度就是 20 g / 0.5 L = 40 g/L。进行除法运算前，务必将体积转换为相同单位。
More concentrated solutions contain a larger mass of solute in the same volume. Diluting a solution by adding more solvent decreases the concentration but does not change the total mass of solute. This concept links to everyday contexts such as mixing squash or making tea.
更浓的溶液在相同体积中含有更多的溶质质量。通过加入更多溶剂来稀释溶液会降低浓度，但不会改变溶质的总质量。这一概念与稀释果汁或泡茶等日常情境相关联。
11. Photosynthesis and Respiration Word Equations | 光合作用与呼吸作用的文字方程式
Plants make their own food through photosynthesis, while all living cells release energy through respiration. The word equations summarise these vital processes and show the reactants and products.
植物通过光合作用制造养料，而所有活细胞通过呼吸作用释放能量。文字方程式总结了这些生命活动，并标明了反应物和生成物。
Photosynthesis:
Carbon dioxide + Water → Glucose + Oxygen
This process requires light energy and chlorophyll. It occurs in the chloroplasts of plant cells. The glucose produced can be used immediately for energy or stored as starch.
该过程需要光能和叶绿素，发生在植物细胞的叶绿体中。产生的葡萄糖可立即用于供能，或转化为淀粉储存起来。
Aerobic respiration:
Glucose + Oxygen → Carbon dioxide + Water (+ energy)
Repiration releases energy for cell activities such as muscle contraction, growth and keeping warm. This reaction takes place in mitochondria. It is the reason we need to breathe in oxygen and breathe out carbon dioxide.
呼吸作用为肌肉收缩、生长和保温等细胞活动释放能量。该反应发生在线粒体中。这就是我们需要吸入氧气、呼出二氧化碳的原因。
12. Key Theorems in Ecology: Pyramids of Number and Energy | 生态学关键定理：数量金字塔与能量金字塔
Ecological pyramids represent the relationship between organisms at different trophic levels in a food chain. The pyramid of number shows the count of individuals, while the pyramid of energy illustrates the 10% energy transfer rule.
生态金字塔表示食物链中不同营养级生物之间的关系。数量金字塔显示个体数量，能量金字塔则阐述了 10% 的能量传递法则。
Pyramid of number: It can be upright or inverted depending on the size of organisms. One oak tree can support thousands of insects, so the base is narrow and the middle level is wide. This is a valid theorem to describe feeding relationships.
数量金字塔：根据生物体的大小，它可能呈正立或倒置。一棵橡树可以养活数千只昆虫，因此塔基狭窄，中间层宽大。这是描述捕食关系的一个有效定理。
Pyramid of energy: Only about 10% of the energy in one trophic level is transferred to the next. This explains why food chains rarely have more than five levels and why there are fewer top predators. The theorem can be summarised as:
能量金字塔：一个营养级中大约只有 10% 的能量转移到下一级。这解释了为什么食物链很少超过五个等级，以及为何顶级掠食者数量较少。该定理可概括为：
Energy transferred ≈ Energy consumed ÷ 10
You can use this rough guide to estimate the mass of prey needed to support a predator. It also highlights the efficiency of eating lower down the food chain.
你可以用这个粗略指南来估算养活一种掠食者所需的猎物质量。它也突显了在食物链较低层级进食的效率。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图