Year 7 Edexcel Science: Essential Formulas & Theorems Quick Reference Handbook | Year 7 Edexcel 科学：公式定理速查手册

📚 Year 7 Edexcel Science: Essential Formulas & Theorems Quick Reference Handbook | Year 7 Edexcel 科学：公式定理速查手册

This handbook collects the key formulas, equations and scientific theorems you will meet in Year 7 Edexcel Science. Use it to check your understanding, practise calculations and build confidence before assessments. Every formula is given in words and symbols, with clear examples.

本手册汇集了你在 Year 7 Edexcel 科学课程中会遇到的重要公式、方程和科学定理。你可以用它来巩固理解、练习计算，并在评估前建立信心。每个公式都同时给出了文字表达式和符号形式，并配有清晰的示例。

1. Speed Equation | 速度公式

Speed measures how far an object travels in a given time. The relationship between speed, distance and time is shown by the formula:

速度衡量物体在给定时间内移动了多远。速度、距离和时间之间的关系可以用以下公式表示：

speed = distance ÷ time

速度 = 距离 ÷ 时间

In symbols, we often write v = d / t or s = d / t. Distance is measured in metres (m), time in seconds (s) and speed in metres per second (m/s). You can rearrange the formula to find distance or time: distance = speed × time and time = distance ÷ speed.

使用符号时，我们常写作 v = d / t 或 s = d / t。距离的单位是米 (m)，时间是秒 (s)，速度是米每秒 (m/s)。你可以通过变形公式求出距离或时间：距离 = 速度 × 时间，时间 = 距离 ÷ 速度。

Quantity	Symbol	SI unit
Speed	v or s	m/s
Distance	d or s	m
Time	t	s

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2. Density Formula | 密度公式

Density tells us how much mass is packed into a certain volume. It explains why some objects float and others sink.

密度表示单位体积内所含的质量，它解释了为什么有的物体会漂浮而有的会下沉。

density = mass ÷ volume

密度 = 质量 ÷ 体积

The symbol equation is ρ = m / V. Mass (m) is measured in kilograms (kg) or grams (g), volume (V) in cubic metres (m³) or cubic centimetres (cm³). Density therefore has units like kg/m³ or g/cm³. To find the mass or volume, simply use mass = density × volume or volume = mass ÷ density.

符号方程式为 ρ = m / V。质量 (m) 的单位是千克 (kg) 或克 (g)，体积 (V) 的单位是立方米 (m³) 或立方厘米 (cm³)。因此密度的单位是 kg/m³ 或 g/cm³。要求质量或体积时，只需使用 质量 = 密度 × 体积 或 体积 = 质量 ÷ 密度。

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3. Weight Equation | 重量公式

Weight is the force of gravity acting on an object. It is not the same as mass – mass is the amount of matter and does not change, while weight depends on gravitational field strength.

重量是作用在物体上的重力。它与质量不同——质量是物质含量的多少，不随位置改变，而重量取决于重力场强度。

weight = mass × gravitational field strength

重量 = 质量 × 重力场强度

W = m g. On Earth, g ≈ 10 N/kg (or 9.8 N/kg). Weight is a force, so it is measured in newtons (N). Mass is measured in kilograms (kg). A 5 kg object on Earth has a weight of about 50 N.

W = m g。在地球上，g 约为 10 N/kg（或 9.8 N/kg）。重量是一种力，因此用牛顿 (N) 作为单位。质量的单位是千克 (kg)。一个质量为 5 kg 的物体在地球上的重量大约为 50 N。

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4. Pressure on Solids | 固体压强

Pressure measures how concentrated a force is over an area. When the same force is spread over a larger area, the pressure decreases.

压强衡量力在面积上的集中程度。当相同的力分散在较大面积上时，压强会减小。

pressure = force ÷ area

压强 = 力 ÷ 面积

P = F / A. Force (F) is in newtons (N), area (A) in square metres (m²), so pressure (P) is in pascals (Pa). 1 Pa = 1 N/m². Understanding pressure helps explain why sharp knives cut more easily and why snowshoes stop you sinking into snow.

P = F / A。力 (F) 的单位为牛顿 (N)，面积 (A) 的单位为平方米 (m²)，因此压强 (P) 的单位为帕斯卡 (Pa)。1 Pa = 1 N/m²。理解压强有助于解释为什么锋利的刀更容易切割，以及为什么雪鞋能防止人陷入雪中。

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5. Work Done Equation | 功的公式

In Science, ‘work done’ means the energy transferred when a force moves an object. Work is done whenever a force causes movement in the direction of the force.

在科学中，“功” 表示力使物体移动时所传递的能量。只要力使物体沿力的方向移动，就做了功。

work done = force × distance (moved in the direction of the force)

功 = 力 × 沿力方向移动的距离

W = F d. Work is also measured in joules (J) because it is a form of energy. 1 joule is the work done when a force of 1 newton moves an object 1 metre.

W = F d。功同样以焦耳 (J) 为单位，因为它是一种能量形式。1 焦耳就是 1 牛顿的力使物体移动 1 米所做的功。

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6. Ohm’s Law | 欧姆定律

Ohm’s Law links voltage, current and resistance in a circuit. It applies to many conductors when temperature remains constant.

欧姆定律将电路中的电压、电流和电阻联系起来。在温度保持不变的条件下，这个定律适用于许多导体。

voltage = current × resistance

电压 = 电流 × 电阻

V = I R. Voltage (V) is in volts (V), current (I) in amperes (A), and resistance (R) in ohms (Ω). You can also write I = V / R or R = V / I.

V = I R。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)。也可以变形为 I = V / R 或 R = V / I。

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7. Hooke’s Law | 胡克定律

Hooke’s Law describes the relationship between the force applied to a spring and how much it stretches. Within the elastic limit, the extension is directly proportional to the force.

胡克定律描述了施加在弹簧上的力与弹簧伸长量之间的关系。在弹性限度内，伸长量与力成正比。

force = spring constant × extension

力 = 弹簧常数 × 伸长量

F = k x. The spring constant (k) tells you how stiff a spring is and is measured in N/m. Extension (x) is the change in length from the original position. If you double the force, the extension doubles – as long as you do not exceed the elastic limit.

F = k x。弹簧常数 (k) 表示弹簧的刚度，单位是 N/m。伸长量 (x) 是弹簧从原长开始变化的长度。只要不超过弹性限度，力增大一倍，伸长量也增大一倍。

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8. Principle of Conservation of Energy | 能量守恒定律

Energy cannot be created or destroyed. It can only be transferred from one store to another or moved between objects. The total energy before and after any change always remains the same.

能量不能被创造或消灭，只能从一个能量储存转移到另一个，或在物体之间传递。任何变化前后，总能量始终保持不变。

For example, when a ball is thrown upwards, kinetic energy is transferred to gravitational potential energy. As it falls, the potential energy transfers back to kinetic energy. Friction and air resistance cause some energy to be transferred to thermal stores, but the overall total never disappears.

例如，将一个球向上抛出时，动能转移到重力势能。当球下落时，势能又转回动能。摩擦和空气阻力会使部分能量转移到热能储存，但总能量从不会消失。

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9. Law of Conservation of Mass | 质量守恒定律

In a chemical reaction, the total mass of the reactants equals the total mass of the products. Atoms are rearranged, not 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。原子只是重新排列，既没有被创造也没有被消灭。

If you burn magnesium in air, the magnesium oxide produced has a mass equal to the original magnesium plus the oxygen that combined with it. In a closed system, no mass is lost. In an open system, gases may escape, giving the impression of a mass change.

如果在空气中燃烧镁，生成的氧化镁的质量等于原来镁的质量加上与之化合的氧气的质量。在封闭系统中，没有质量损失。在开放系统中，气体可能逸出，从而造成质量改变的假象。

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10. Microscope Magnification | 显微镜放大率

The total magnification of a light microscope is the product of the eyepiece lens magnification and the objective lens magnification.

光学显微镜的总放大倍率是目镜放大倍率与物镜放大倍率的乘积。

total magnification = eyepiece magnification × objective magnification

总放大倍率 = 目镜放大倍率 × 物镜放大倍率

If the eyepiece lens is ×10 and the objective lens is ×40, the total magnification is ×400. This formula is used every time you set up a microscope to view cells.

如果目镜是 10 倍，物镜是 40 倍，那么总放大倍率就是 400 倍。每次使用显微镜观察细胞时，都会用到这个公式。

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11. Photosynthesis Word Equation | 光合作用文字方程式

Photosynthesis is the process by which green plants make their own food using light energy. The word equation summarises the reactants and products.

光合作用是绿色植物利用光能制造自身养料的过程。文字方程式概括了反应物和生成物。

carbon dioxide + water → glucose + oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

This reaction occurs in the chloroplasts of plant cells, and light energy is absorbed by chlorophyll. Glucose is used by the plant for energy and growth; oxygen is released as a by-product.

该反应发生在植物细胞的叶绿体内，光能被叶绿素吸收。葡萄糖供植物用于能量和生长，氧气则作为副产品释放出来。

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12. Aerobic Respiration Word Equation | 有氧呼吸文字方程式

Aerobic respiration releases energy from glucose in the presence of oxygen. It takes place in the mitochondria of living cells.

有氧呼吸在有氧气存在的条件下从葡萄糖中释放能量，发生在活细胞的线粒体中。

glucose + oxygen → carbon dioxide + water

葡萄糖 + 氧气 → 二氧化碳 + 水

This equation shows that respiration is essentially the reverse of photosynthesis in terms of chemicals. The energy released is used for movement, growth and keeping warm.

这个方程式表明，就化学物质而言，呼吸作用在本质上与光合作用相反。释放的能量用于运动、生长和维持体温。

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