📚 Year 7 SQA Science: Formula & Theorem Quick Reference Handbook | Year 7 SQA 科学：公式定理速查手册
This handbook is designed to help you quickly recall the key formulas, laws, and word equations you will encounter in Year 7 SQA Science. Use it as a revision aid to build confidence when tackling calculations and explaining scientific phenomena. Each entry includes the formula, symbol meanings, standard units, and a worked example where appropriate.
这本手册旨在帮助你快速回顾 Year 7 SQA 科学中遇到的关键公式、定律和文字方程式。你可以将它用作复习工具，在处理计算和解释科学现象时增强信心。每个条目都包含公式、符号含义、标准单位以及适当的示例。
1. Speed, Distance and Time | 速度、距离和时间
Average Speed = Total Distance ÷ Total Time
This formula shows how fast an object moves on average over a journey. It is one of the most fundamental relationships in physics and is used whenever motion is uniform.
这个公式表示物体在一段行程中的平均移动速度。它是物理学中最基本的关系之一，可用于所有匀速运动的情况。
Symbols: v stands for speed, d for distance travelled and t for the time taken. Speed is a scalar quantity, so it only has size, not direction.
符号：v 代表速度，d 代表移动的距离，t 代表所用的时间。速度是标量，只有大小没有方向。
Common units are metres per second (m/s) and kilometres per hour (km/h). To change m/s into km/h, multiply by 3.6.
常用单位是米每秒 (m/s) 和千米每小时 (km/h)。将 m/s 换算成 km/h 需要乘以 3.6。
| Quantity | Symbol | SI Unit | Other Units |
| Speed | v | m/s | km/h, mph |
| Distance | d | m | km, cm |
| Time | t | s | h, min |
ers a distance of 30 km in 1.5 hours. Her average speed is 30 km ÷ 1.5 h = 20 km/h.
示例：一名自行车手用 1.5 小时骑行了 30 km。她的平均速度为 30 km ÷ 1.5 h = 20 km/h。
2. Density, Mass and Volume | 密度、质量和体积
Density = Mass ÷ Volume
Density describes how much mass is packed into a certain volume. It helps to explain why some objects float while others sink, and it is a characteristic property of materials.
密度描述单位体积内所含质量的大小。它有助于解释为什么有些物体会浮起而有些会下沉，并且是物质的一种特性。
The symbol for density is the Greek letter rho (ρ), but often we simply use D. Mass is m and volume is V.
密度的符号是希腊字母 ρ，但我们也常用 D 表示。质量的符号是 m，体积的符号是 V。
ty then has units like g/cm³ or kg/m³. Note that 1 g/cm³ = 1000 kg/m³;.
单位：质量用克 (g) 或千克 (kg) 计量；体积用立方厘米 (cm³) 或立方米 (m³) 计量。因此密度的单位是 g/cm³ 或 kg/m³。注意 1 g/cm³ = 1000 kg/m³;。
0 g and a volume of 50 cm³. Its density is 200 g ÷ 50 cm³ = 4 g/cm³;.
示例：一块金属的质量为 200 g，体积为 50 cm³。它的密度为 200 g ÷ 50 cm³ = 4 g/cm³;。
3. Pressure, Force and Area | 压力、力和面积
Pressure = Force ÷ Area
Pressure tells us how concentrated a force is. A sharp knife cuts easily because the same force is applied over a very small area, giving a high pressure.
压力表示力的集中程度。锋利的刀容易切割，是因为同样的力作用在非常小的面积上，产生了较大的压力。
We use P for pressure, F for force and A for area. Force is measured in newtons (N) and area in square metres (m²). Pressure therefore has the unit N/m², also called the pascal (Pa).
压力用 P 表示，力用 F，面积用 A。力的单位是牛顿 (N)，面积单位是平方米 (m²)。所以压力的单位是 N/m²，也称为帕斯卡 (Pa)。
of 500 N acts on an area of 2 m². The pressure is 500 N ÷ 2 m² = 250 Pa.
示例：一个 500 N 的力作用在 2 m² 的面积上。压力为 500 N ÷ 2 m² = 250 Pa。
4. Weight, Mass and Gravity | 重量、质量和重力
Weight = Mass × Gravitational Field Strength
Weight is the force of gravity acting on an object. It should not be confused with mass, which is the amount of matter in an object and does not change with location.
重量是作用在物体上的重力。不要将重量与质量混淆，质量是物体所含物质的多少，不随位置改变。
The formula is W = m × g, where g is the gravitational field strength. On Earth, g is approximately 10 N/kg (more precisely 9.8 N/kg). On the Moon, g is only about 1.6 N/kg.
公式为 W = m × g，其中 g 是重力场强度。在地球表面，g 约等于 10 N/kg（更精确为 9.8 N/kg）。在月球上，g 仅约 1.6 N/kg。
Units: weight in newtons (N), mass in kilograms (kg). Always use kg when inserting into the equation.
单位：重量用牛顿 (N)，质量用千克 (kg)。代入方程时务必使用 kg 为单位。
xample: A textbook has a mass of 2 kg. Its weight on Earth is 2 kg × 10 N/kg = 20 N.
示例：一本教科书的质量为 2 kg。它在地球上的重量为 2 kg × 10 N/kg = 20 N。
5. Hooke's Law | 胡克定律
Force = Spring Constant × Extension
Hooke's Law describes the behaviour of springs and other elastic objects. It states that the extension (or compression) is directly proportional to the applied force, provided the elastic limit is not exceeded.
胡克定律描述了弹簧和其他弹性物体的行为。它指出，只要不超过弹性极限，伸长量（或压缩量）与所施加的力成正比。
In symbols: F = k × x. Here F is the force in newtons (N), k is the spring constant (stiffness) in N/m, and x is the extension in metres (m). Extension = stretched length − original length.
符号表示为：F = k × x。其中 F 是力 (N)，k 是弹簧常数（刚度，单位 N/m），x 是伸长量 (m)。伸长量 = 拉伸后的长度 − 原来的长度。
A stiffer spring has a larger k value, meaning more force is needed to stretch it by the same amount.
刚度越大的弹簧，k 值越大，意味着要产生相同的伸长量需要更大的力。
e extension is 10 N ÷ 50 N/m = 0.2 m (20 cm), as long as the limit is not exceeded.
示例：一根弹簧的常数为 50 N/m。施加 10 N 的力时，伸长量为 10 N ÷ 50 N/m = 0.2 m (20 cm)，前提是未超过弹性极限。
6. Ohm's Law | 欧姆定律
Voltage = Current × Resistance
Ohm's Law is the basic rule for electric circuits. It links the potential difference across a component, the current flowing through it and its resistance. It holds true for ohmic conductors at constant temperature.
欧姆定律是电路的基本规律。它关联了元件两端的电势差、流过它的电流以及电阻。在恒温条件下，欧姆定律适用于欧姆导体。
The equation is written as V = I × R. V is voltage in volts (V), I is current in amperes (A), and R is resistance in ohms (Ω).
公式写作 V = I × R。V 是电压，单位伏特 (V)；I 是电流，单位安培 (A)；R 是电阻，单位欧姆 (Ω)。
If the resistance stays the same, doubling the voltage will double the current. This proportional relationship is very useful when designing and analysing circuits.
如果电阻不变，电压加倍会使电流加倍。这种比例关系在电路设计和分析中非常有用。
of 0.5 A flows through it. The voltage across the lamp is 0.5 A × 10 Ω = 5 V.
示例：一盏灯的电阻为 10 Ω，通过它的电流为 0.5 A。灯两端的电压为 0.5 A × 10 Ω = 5 V。
7. Power, Energy and Time | 功率、能量和时间
Power = Energy Transferred ÷ Time
Power measures how quickly energy is transferred or work is done. A powerful machine does the same amount of work in a shorter time.
功率衡量能量传递或做功的快慢。一台大功率的机器能用更短的时间完成同样的功。
In equation form: P = E ÷ t. P stands for power in watts (W), E for energy in joules (J), and t for time in seconds (s). 1 watt = 1 joule per second.
公式形式：P = E ÷ t。P 代表功率，单位瓦特 (W)；E 代表能量，单位焦耳 (J)；t 代表时间，单位秒 (s)。1 瓦特 = 1 焦耳每秒。
This relationship applies to both mechanical and electrical systems. For example, a light bulb rated at 60 W converts 60 J of electrical energy into light and heat every second.
这一关系适用于机械系统和电系统。例如，一个标称 60 W 的灯泡每秒钟将 60 J 的电能转化为光和热。
ic motor transfers 300 J of energy in 10 seconds. Its power is 300 J ÷ 10 s = 30 W.
示例：一台电动机在 10 秒内传递了 300 J 的能量。它的功率为 300 J ÷ 10 s = 30 W。
8. Law of Reflection | 反射定律
Angle of Incidence = Angle of Reflection
When light (or other waves) bounces off a smooth surface, it follows the law of reflection. This principle allows us to see images in mirrors and to predict how light will travel.
当光（或其他波）从光滑表面反弹时，它遵循反射定律。这一原理让我们能在镜子中看到图像，并能预测光的传播路径。
All angles are measured from the normal, an imaginary line drawn perpendicular to the surface at the point of incidence. The incoming ray is called the incident ray, and the outgoing ray is the reflected ray.
所有角度都从法线量起，法线是在入射点垂直于镜面的一条假想线。入射光线称为入射线，出射光线称为反射线。
If the incident ray strikes the mirror at 30° to the normal, the reflected ray will leave at exactly 30° on the opposite side. This is true for all flat mirrors.
如果入射线以与法线成 30° 的角度射向镜面，反射线将以完全相同的 30° 角从另一侧离开。这对所有平面镜都成立。
Rough surfaces scatter light in many directions because the normal at each point is different, which is called diffuse reflection.
粗糙表面由于各点的法线方向不同，会把光向各个方向散射，这叫作漫反射。
9. Law of Conservation of Mass | 质量守恒定律
Total Mass of Reactants = Total Mass of Products
In a chemical reaction, atoms are not created or destroyed; they are simply rearranged. Therefore, the total mass before the reaction equals the total mass after the reaction.
在化学反应中，原子既不会创生也不会消失，只是重新排列。因此，反应前的总质量等于反应后的总质量。
This law is vital when balancing chemical equations. If a reaction appears to lose mass, it is usually because a gas has escaped into the air. If it gains mass, a gas from the air has likely combined with the reactants.
这一定律在配平化学方程式时至关重要。如果反应似乎失去了质量，通常是因为气体散逸到了空气中。如果质量增加，很可能是空气中的气体与反应物发生了结合。
Example: When magnesium ribbon burns in air, it combines with oxygen to form magnesium oxide. The magnesium oxide has a greater mass than the original ribbon because mass from oxygen has been added. The total mass of the system (ribbon + oxygen) remains constant.
示例：镁条在空气中燃烧时与氧气结合生成氧化镁。氧化镁的质量比原来的镁条大，因为增加了氧的质量。整个系统（镁条 + 氧气）的总质量保持不变。
10. Photosynthesis Word Equation | 光合作用文字方程式
Carbon Dioxide + Water → Glucose + Oxygen
Photosynthesis is the process green plants use to make their own food. It requires light energy and chlorophyll to drive the reaction.
光合作用是绿色植物制造自己食物的过程。它需要光能和叶绿素来驱动反应。
The word equation summarises the raw materials and products. Carbon dioxide is taken from the air through stomata, and water is absorbed by the roots. Glucose is used for energy and growth, while oxygen is released as a by-product.
这个文字方程式概括了原料和产物。二氧化碳通过气孔从空气中吸收，水由根部吸收。葡萄糖用于提供能量和生长，氧气则作为副产品释放。
The conditions written above the arrow are 'light energy' and 'chlorophyll'. Without these, the reaction cannot happen.
箭头上方标注的条件是“光能”和“叶绿素”。没有这些，反应就无法进行。
Plants also use some of the glucose to make other substances like starch (for storage) and cellulose (for cell walls).
植物也会将部分葡萄糖转化为其他物质，如淀粉（用于储存）和纤维素（用于细胞壁）。
11. Aerobic Respiration Word Equation | 有氧呼吸文字方程式
Glucose + Oxygen → Carbon Dioxide + Water (+ Energy)
Aerobic respiration is the process that releases energy from glucose in the cells of most living organisms. It uses oxygen and occurs continuously to support vital functions.
有氧呼吸是大多数生物体内细胞从葡萄糖中释放能量的过程。它需要氧气，并持续进行以支持生命活动。
Energy is shown in brackets because it is not a chemical substance but is released to fuel activities such as muscle contraction, growth and keeping warm.
能量用括号表示，因为它不是一种化学物质，但被释放出来为肌肉收缩、生长和保持体温等活动提供能量。
The reactants are glucose (from food) and oxygen (from breathing). The products are carbon dioxide and water, which are exhaled or removed from the body.
反应物是葡萄糖（来自食物）和氧气（来自呼吸）。产物是二氧化碳和水，通过呼气或从身体排出。
This reaction can be remembered as the reverse of photosynthesis in terms of reactants and products, though the two processes serve completely different purposes in nature.
这个反应可以从反应物和产物上记忆为光合作用的逆过程，然而在自然界中这两个过程有着完全不同的目的。
12. Moments (Turning Effect) | 力矩（转动效应）
Moment of a Force = Force × Perpendicular Distance from Pivot
A moment is the turning effect of a force. Spanners, door handles and seesaws all make use of moments to make jobs easier.
力矩是力的转动效应。扳手、门把手和跷跷板都利用力矩来让工作更省力。
In symbols: M = F × d. F is the force in newtons (N), d is the perpendicular distance from the pivot to the line of action of the force in metres (m). The unit of moment is newton metre (Nm).
符号表示：M = F × d。F 是力 (N)，d 是从支点到力作用线的垂直距离 (m)。力矩的单位是牛顿米 (Nm)。
To balance a see-saw, the clockwise moments must equal the anticlockwise moments. This principle is known as the principle of moments.
要使跷跷板平衡，顺时针力矩必须等于逆时针力矩。这一原理称为力矩原理。
1 m from the pivot, they must provide 400 N to balance (since 400 N × 1 m = 400 Nm).
示例：一个孩子在离支点 2 m 处施加 200 N 的力。力矩为 200 N × 2 m = 400 Nm。如果对面的另一个孩子坐在离支点 1 m 处，
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