Complete Physics for Cambridge Secondary Workbook: Key Concepts Explained | 剑桥中学物理全解：核心概念解析

📚 Complete Physics for Cambridge Secondary Workbook: Key Concepts Explained | 剑桥中学物理全解：核心概念解析

This article provides a clear, topic-by-topic explanation of the key concepts found in the Complete Physics for Cambridge Secondary 1 Workbook. Designed for students and teachers, it breaks down essential ideas – from measurement and forces to energy and waves – in a way that is easy to follow and builds a solid foundation for IGCSE Physics. Each section is presented in paired English and Chinese paragraphs to support bilingual learning.

本文针对《Complete Physics for Cambridge Secondary 1 Workbook》中的核心概念，进行逐主题的清晰解析。文章旨在为教师和学生提供易于理解的讲解，涵盖从测量和力到能量、波动等基础知识，为 IGCSE 物理学习打下坚实基础。为支持双语学习，每个要点均提供中英文对照的段落说明。

1. Measurements and Units | 测量与单位

All physical quantities require a number and a unit. In physics, we use the International System of Units (SI). Length is measured in metres (m), mass in kilograms (kg), time in seconds (s), and temperature in kelvin (K) or degrees Celsius (°C). Correct use of prefixes such as kilo- (10³), centi- (10⁻²) and milli- (10⁻³) allows us to express very large or very small values conveniently.

一切物理量都需同时给出数值和单位。物理学中使用国际单位制（SI）。长度用米（m），质量用千克（kg），时间用秒（s），温度用开尔文（K）或摄氏度（°C）。正确使用词头，如千（10³）、厘（10⁻²）、毫（10⁻³），能够方便地表达很大或很小的数值。

Measuring instruments have a certain precision. The measurement’s uncertainty is often taken as half the smallest scale division. For example, a ruler marked in millimetres gives a reading uncertainty of ±0.5 mm. When taking multiple readings, we reduce random error by calculating the mean.

测量仪器具有一定的精确度。测量的不确定度通常取为最小刻度值的一半。例如，一把毫米刻度尺的读数不确定度为 ±0.5 mm。通过多次测量并计算平均值，可以减小随机误差。

• Scalar quantities: magnitude only (e.g., distance, speed, mass). / 标量：只有大小的量（如距离、速率、质量）。
• Vector quantities: magnitude and direction (e.g., displacement, velocity, force). / 矢量：既有大小又有方向的量（如位移、速度、力）。

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2. The Particle Model of Matter | 物质粒子模型

Matter is made up of tiny particles (atoms, molecules or ions) that are in constant random motion. The particle model explains the behaviour of solids, liquids and gases. In a solid, particles are closely packed in a fixed arrangement and can only vibrate about fixed positions. In a liquid, particles are still close together but can move past one another. In a gas, particles are far apart and move rapidly in all directions.

物质由极其微小的粒子（原子、分子或离子）组成，它们不停地做无规则运动。粒子模型解释了固体、液体和气体的行为。固体中，粒子紧密排列在固定位置上，只能振动；液体中，粒子仍然靠得很近，但可以相互滑动；气体中，粒子相距很远，快速地向所有方向运动。

Changes of state occur when energy is added or removed. Melting, boiling and evaporation require energy input; condensation, freezing and deposition release energy. The mass is conserved during a state change because the number of particles does not change.

当能量被加入或移除时就会发生物态变化。熔化、沸腾和蒸发需要吸收能量；凝结、凝固和凝华释放能量。物态变化过程中质量守恒，因为粒子总数没有改变。

• Brownian motion: random movement of visible particles (e.g., smoke particles) caused by collisions with invisible air molecules. / 布朗运动：可见粒子（如烟雾颗粒）因受到不可见的空气分子碰撞所做的无规则运动。

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3. Forces and Motion | 力与运动

A force is a push or a pull that can change an object’s shape, speed or direction. The unit of force is the newton (N). Forces can be contact forces (e.g., friction, tension) or non-contact forces (e.g., gravity, magnetic force). When several forces act on an object, we find the resultant force by vector addition.

力是推或拉的作用，能够改变物体的形状、速度或运动方向。力的单位是牛顿（N）。力可以是接触力（如摩擦力、张力）或非接触力（如重力、磁力）。当多个力同时作用在一个物体上时，我们通过矢量加法求出合力。

Newton’s First Law states that an object remains at rest or moves with constant velocity unless a resultant force acts on it. Newton’s Second Law links force, mass and acceleration: F = m × a. Acceleration is measured in m/s². An object with a larger mass needs a greater force to achieve the same acceleration.

牛顿第一定律指出，除非有合力作用，否则物体将保持静止或匀速直线运动状态。牛顿第二定律将力、质量和加速度联系在一起：F = m × a。加速度的单位是 m/s²。质量越大的物体，要达到同样的加速度就需要越大的力。

F = m × a

For falling objects near Earth’s surface, air resistance increases with speed. When air resistance equals weight, the resultant force becomes zero and the object falls at constant speed – this is terminal velocity.

对于地球表面附近的落体，空气阻力随速度增大而增加。当空气阻力等于重力时，合力为零，物体以恒定速度下落——这就是终极速度。

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4. Energy Transforms and Conservation | 能量转换与能量守恒

Energy is the ability to do work. The SI unit of energy is the joule (J). Energy exists in different stores: chemical, kinetic, gravitational potential, elastic potential, thermal, nuclear and electromagnetic. Energy can be transferred from one store to another by heating, doing work, or by radiation.

能量是做功的能力。能量的国际单位是焦耳（J）。能量存在于不同的“仓库”中：化学能、动能、重力势能、弹性势能、内能（热能）、核能和电磁能。能量可以通过加热、做功或辐射，从一个仓库转移到另一个仓库。

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or converted. In any process, the total energy remains constant. For example, when a ball is thrown upwards, kinetic energy is converted to gravitational potential energy; as it falls, the reverse happens, neglecting air resistance.

能量守恒定律指出，能量既不能被创造也不能被消灭，只能被转移或转换。在任何过程中，总能量保持不变。例如，向上抛球时，动能转换为重力势能；下落时忽略空气阻力则发生相反转换。

Work done is calculated as force × distance moved in the direction of the force. Work done (J) = force (N) × distance (m). Power is the rate of doing work: P = W / t, measured in watts (W).

做功等于力乘以沿力方向移动的距离。做功（J）= 力（N）× 距离（m）。功率是做功的速率：P = W / t，单位是瓦特（W）。

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5. Heat Transfer: Conduction, Convection and Radiation | 热传递：传导、对流与辐射

Heat can be transferred in three ways: conduction, convection and radiation. Conduction occurs mainly in solids, where vibrating particles pass kinetic energy to neighbouring particles without the material itself moving. Metals are good conductors because they have free electrons that can transfer energy quickly.

热传递有三种方式：传导、对流和辐射。传导主要发生在固体中，振动的粒子将动能传递给相邻粒子，但物质本身并不移动。金属是热的良导体，因为它们拥有能够快速传递能量的自由电子。

Convection takes place in fluids (liquids and gases). When a fluid is heated, it expands, becomes less dense and rises. Cooler, denser fluid sinks to take its place, setting up a convection current. This is how hot air balloons rise and how ocean currents form.

对流发生在流体（液体和气体）中。流体受热时膨胀，密度变小而上升；较冷、密度较大的流体下沉补充，从而形成对流循环。热气球正是因此上升，海流也是这样形成的。

Infrared radiation is a form of electromagnetic wave that can travel through a vacuum. All objects emit and absorb infrared radiation. Dark, matt surfaces are good absorbers and emitters, while light, shiny surfaces are good reflectors and poor emitters.

红外辐射是一种可在真空中传播的电磁波。所有物体都会发射和吸收红外辐射。黑暗粗糙的表面是良好的吸收体和辐射体，而浅色光亮的表面则是良好的反射体和较差的辐射体。

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6. Density and Pressure | 密度与压强

Density is mass per unit volume: ρ = m / V. The unit is kg/m³ or g/cm³. The density of a material does not change with the size of the sample; it is a characteristic property. Solids are usually denser than liquids, and liquids are much denser than gases.

密度是单位体积的质量：ρ = m / V。单位是 kg/m³ 或 g/cm³。物质的密度不随样本大小而改变，它是一种特征性质。固体通常比液体密度大，液体又远比气体密度大。

Pressure is the force acting per unit area: P = F / A. The unit is the pascal (Pa), where 1 Pa = 1 N/m². Pressure in a liquid increases with depth and density: P = hρg, where h is depth and g is gravitational field strength. Atmospheric pressure is about 101 000 Pa at sea level.

压强是单位面积上承受的压力：P = F / A。单位是帕斯卡（Pa），1 Pa = 1 N/m²。液体的压强随深度和密度的增加而增大：P = hρg，其中 h 为深度，g 为重力场强度。海平面的大气压强约 101 000 Pa。

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7. Wave Properties: Sound and Light | 波的性质：声与光

A wave transfers energy without transferring matter. Transverse waves (e.g., light, water waves) have vibrations perpendicular to the direction of energy transfer. Longitudinal waves (e.g., sound) have vibrations parallel to the direction of energy transfer, consisting of compressions and rarefactions.

波传递能量而不传递物质。横波（如光波、水波）的振动方向与能量传递方向垂直。纵波（如声波）的振动方向与能量传递方向平行，由疏部和密部组成。

Key wave quantities: frequency (f) in hertz (Hz), wavelength (λ) in metres, and wave speed (v) in m/s. The wave equation is v = f λ. Reflection, refraction and diffraction are common wave behaviours. Sound requires a medium to travel; light does not, and its speed in vacuum is 3.0 × 10⁸ m/s.

波的关键物理量：频率（f）以赫兹（Hz）为单位，波长（λ）以米为单位，波速（v）以 m/s 为单位。波速方程为 v = f λ。反射、折射和衍射是常见的波动现象。声波的传播需要介质，光则不需要，其在真空中的速度为 3.0 × 10⁸ m/s。

v = f λ

• Echo: reflection of sound. / 回声：声的反射。
• Refraction: change in wave speed and direction when entering a new medium. / 折射：波进入新介质时速率和方向发生改变。

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8. Electric Circuits | 电路

An electric current is a flow of charge. In metals, current is carried by moving electrons. Current (I) is measured in amperes (A), potential difference (V) in volts (V), and resistance (R) in ohms (Ω). Ohm’s Law relates these: V = I × R, provided temperature remains constant.

电流是电荷的流动。在金属中，电流由移动的电子承载。电流（I）以安培（A）为单位，电势差（V）以伏特（V）为单位，电阻（R）以欧姆（Ω）为单位。欧姆定律将它们联系起来：V = I × R，前提是温度保持恒定。

In a series circuit, the current is the same at all points, and the total resistance is the sum of individual resistances. In a parallel circuit, the potential difference across each branch is the same, and the total current is the sum of the branch currents. Measuring instruments: ammeters are connected in series, voltmeters in parallel.

串联电路中，各点电流相等，总电阻等于各电阻之和。并联电路中，各支路两端电压相同，总电流等于各支路电流之和。测量仪表：电流表串联在电路中，电压表并联在待测元件两端。

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9. Magnetism and Electromagnets | 磁性与电磁铁

A magnet has a north and a south pole. Like poles repel; unlike poles attract. The magnetic field is strongest at the poles. Magnetic materials, such as iron, nickel and cobalt, can be magnetised. Permanent magnets retain their magnetism, while soft magnetic materials (e.g., iron) lose it easily and are used in temporary magnets.

磁体有北极和南极。同名磁极相互排斥，异名磁极相互吸引。磁极处的磁场最强。铁、镍、钴等磁性材料可以被磁化。永磁体可以长期保持磁性，而软磁材料（如铁）容易失磁，常被用来制作暂时磁体。

An electromagnet is a coil of wire (solenoid) with a current passing through it. The strength of an electromagnet can be increased by increasing the current, adding more turns to the coil, or inserting a soft iron core. Electromagnets are used in relays, electric bells and lifting scrap metal.

电磁铁是一个通有电流的线圈（螺线管）。电磁铁的磁性强弱可以通过增大电流、增加线圈匝数或插入软铁芯来提高。电磁铁广泛应用于继电器、电铃和起重废铁等场合。

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10. Earth and the Solar System | 地球与太阳系

The Earth rotates on its axis once every 24 hours, causing day and night. It revolves around the Sun once every 365.25 days, giving rise to the year and the seasons. The Moon orbits the Earth every 27.3 days and reflects light from the Sun. Phases of the Moon are due to the changing relative positions of the Earth, Moon and Sun.

地球每 24 小时自转一周，形成了昼夜交替。地球每 365.25 天绕太阳公转一周，形成了年和四季。月球每 27.3 天绕地球运行一周，并反射太阳光。月相的变化是由日、地、月三者相对位置的改变造成的。

The Solar System consists of the Sun, eight planets, their moons, and smaller bodies such as asteroids and comets. The planets in order from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Gravity provides the centripetal force that keeps planets in nearly circular orbits.

太阳系包括太阳、八大行星及其卫星，以及小行星和彗星等较小天体。按距离太阳由近到远排列，行星依次为：水星、金星、地球、火星、木星、土星、天王星和海王星。引力提供了行星沿近似圆形轨道运动所需的向心力。

Planet 行星	Type 类型	Notable feature 显著特征
Mercury 水星	Terrestrial 类地行星	Closest to the Sun 最靠近太阳
Jupiter 木星	Gas giant 气态巨行星	Largest planet 最大行星
Saturn 土星	Gas giant 气态巨行星	Prominent ring system 显著光环

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11. Resources and Sustainability | 资源与可持续性

Energy resources are classified as renewable or non-renewable. Non-renewable sources include fossil fuels (coal, oil, natural gas) and nuclear fuels. They are finite and cause environmental problems such as CO₂ emission and radioactive waste. Renewable sources, e.g., solar, wind, hydroelectric, tidal and geothermal, are replenished naturally and generally have a smaller environmental impact.

能源分为可再生与不可再生两类。不可再生能源包括化石燃料（煤、石油、天然气）和核燃料。它们的储量有限，且会引起二氧化碳排放和放射性废物等环境问题。可再生能源如太阳能、风能、水力、潮汐能和地热能可自然补充，对环境的影响通常较小。

Energy transfers always involve some energy dissipated as thermal energy to the surroundings. Improving efficiency means reducing wasted energy. For example, using insulation in buildings or streamlining vehicles reduces unwanted heat loss and air resistance. Making responsible energy choices is vital for sustainability.

能量转换中总会有部分能量以热能形式散失到周围环境。提高效率意味着减少浪费的能量。例如，在建筑物中使用隔热材料或使交通工具表面流线型，可以减少不必要的热损耗和空气阻力。为促进可持续发展，负责任地选择能源至关重要。

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