📚 Core Knowledge Review of KS3 CIE Physics | KS3 CIE 物理：核心知识点梳理
This article provides a comprehensive review of the core topics in the Cambridge Lower Secondary (KS3) Physics syllabus, aligned with the CIE checkpoint. Mastering these fundamentals is essential for building a strong foundation in physics.
本文全面梳理了剑桥初中（KS3）物理课程的核心知识点，对标 CIE checkpoint 考试。掌握这些基础知识对于打好物理基础至关重要。
1. Forces | 力
A force is a push or a pull acting on an object. Forces can change the speed, direction, or shape of an object. The unit of force is the newton (N), named after Sir Isaac Newton.
力是作用在物体上的推或拉。力可以改变物体的速度、方向或形状。力的单位是牛顿 (N)，以艾萨克·牛顿爵士命名。
Forces are measured using a newton meter (spring balance). Types of forces include gravity, friction, air resistance, tension, upthrust, and magnetic force. Forces can be contact forces (e.g. friction) or non-contact forces (e.g. gravitational force).
力用牛顿计（弹簧秤）来测量。力的种类包括重力、摩擦力、空气阻力、张力、浮力和磁力。力可以是接触力（如摩擦力）或非接触力（如引力）。
When multiple forces act on an object, they can be replaced by a single resultant force. If the resultant force is zero, the forces are balanced and the object remains at rest or moves at a constant speed. If the resultant force is not zero, the forces are unbalanced, causing acceleration or deceleration.
当多个力作用在同一物体上时，可以用一个合力来代替。如果合力为零，则力平衡，物体保持静止或匀速运动。如果合力不为零，则力不平衡，导致加速或减速。
The weight of an object is the gravitational force pulling it towards the centre of the Earth. Weight is different from mass. The equation that links weight, mass and gravitational field strength is:
物体的重量是将其拉向地心的引力。重量与质量不同。重量、质量和引力场强度之间的关系式为：
W = m × g
重量 = 质量 × 引力场强度
where W is weight in newtons (N), m is mass in kilograms (kg), and g is gravitational field strength in newtons per kilogram (N/kg). On Earth, g is approximately 10 N/kg.
其中 W 为重量（N），m 为质量（kg），g 为引力场强度（N/kg）。地球表面的 g 约为 10 N/kg。
2. Motion | 运动
The speed of an object tells us how fast it is moving. It is a scalar quantity and can be calculated using the formula:
速度告诉我们物体运动的快慢。它是一个标量，可以用以下公式计算：
speed = distance ÷ time
速度 = 路程 ÷ 时间
where distance is measured in metres (m) or kilometres (km), and time in seconds (s) or hours (h). The SI unit of speed is metres per second (m/s).
其中路程以米 (m) 或千米 (km) 为单位，时间以秒 (s) 或小时 (h) 为单位。速度的国际单位是米每秒 (m/s)。
A distance-time graph shows how far an object has travelled over time. A straight sloping line represents constant speed, while a horizontal line indicates the object is stationary. The slope (gradient) of the line gives the speed.
路程-时间图显示了物体随时间移动的距离。一条倾斜的直线代表匀速运动，水平线表示物体静止。直线的斜率（梯度）代表速度。
Relative speed is the speed of one object as observed from another. When two objects move in the same direction, relative speed is the difference in their speeds; when they move towards each other, it is the sum of their speeds.
相对速度是从一个物体观察另一个物体的速度。同向运动时，相对速度是两者速度之差；相向运动时，相对速度是两者速度之和。
3. Energy | 能量
Energy is the ability to do work. It exists in many forms: kinetic, gravitational potential, elastic potential, thermal (heat), chemical, electrical, light, and sound. Energy is measured in joules (J).
能量是做功的能力。它有许多形式：动能、重力势能、弹性势能、热能、化学能、电能、光能和声能。能量的单位是焦耳 (J)。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another. In any energy transfer, some energy is always dissipated (wasted) as heat, which raises the temperature of the surroundings.
能量守恒定律指出，能量不会凭空产生或消失，只会从一种形式转化为另一种形式。在任何能量转移中，总有一部分能量以热的形式耗散（浪费），使环境温度升高。
Sankey diagrams are used to visualise energy transfers. The width of the arrows represents the amount of energy; useful energy is shown as an arrow continuing in the original direction, while wasted energy is shown branching downwards or upwards.
桑基图用于直观展示能量转移。箭头的宽度代表能量的多少；有用能箭头继续向前，浪费的能箭头则分支向下或向上。
Renewable energy resources are those that can be replenished in a short time, such as solar, wind, hydroelectric, wave, tidal, geothermal, and biomass. Non-renewable resources like fossil fuels (coal, oil, natural gas) and nuclear fuel are finite and will run out.
可再生能源是短期内可补充的能源，如太阳能、风能、水电、波浪能、潮汐能、地热和生物质。非可再生能源如化石燃料（煤、石油、天然气）和核燃料有限，终将耗尽。
The efficiency of an energy transfer is calculated as:
能量转移的效率计算公式为：
efficiency = (useful energy output ÷ total energy input) × 100%
效率 = (有用的能量输出 ÷ 总能量输入) × 100%
No device can be 100% efficient because some energy is invariably lost to thermal energy.
没有设备能达到 100% 的效率，因为总有部分能量转化为热能损失。
4. Sound | 声
Sound is produced by vibrating objects. These vibrations travel through a medium (solid, liquid, or gas) as longitudinal waves. Sound cannot travel through a vacuum because there are no particles to carry the vibrations.
声音由振动的物体产生。这些振动以纵波的形式在介质（固体、液体或气体）中传播。声音不能在真空中传播，因为没有粒子传递振动。
The frequency of a sound wave is the number of vibrations per second, measured in hertz (Hz). Frequency determines the pitch: a high frequency gives a high pitch, and a low frequency gives a low pitch.
声波的频率是每秒振动的次数，单位是赫兹 (Hz)。频率决定音调：频率高则音调高，频率低则音调低。
The amplitude of a wave is the maximum displacement from the rest position. Amplitude determines the loudness of the sound: a larger amplitude corresponds to a louder sound. Loudness is measured in decibels (dB).
振幅是波偏离平衡位置的最大位移。振幅决定响度：振幅越大，声音越响。响度用分贝 (dB) 测量。
The speed of sound in air is approximately 343 m/s at room temperature. Sound travels faster in liquids than in gases, and fastest in solids because particles are closer together.
声音在空气中的速度在室温下约为 343 m/s。声音在液体中的传播速度比气体快，在固体中最快，因为粒子排列更紧密。
Ultrasound refers to sound waves with frequencies above 20 000 Hz, which is beyond the range of human hearing. Ultrasound is used in medical imaging (e.g. prenatal scans) and industrial cleaning.
超声波是指频率超过 20 000 Hz 的声波，超出人耳听觉范围。超声波用于医学成像（如产前检查）和工业清洗。
5. Light | 光
ght can travel through a vacuum at a speed of approximately 300 000 000 m/s (3 × 10⁸ m/s).
光沿直线传播。我们在图中用光线表示其路径。光可以在真空中传播，速度约为 300 000 000 m/s（3 × 10⁸ m/s）。
When light hits a smooth surface, it reflects. The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal (a line perpendicular to the surface).
光照射到光滑表面时会发生反射。反射定律指出，入射角等于反射角，两者均从法线（垂直于表面的线）测量。
Refraction occurs when light passes from one medium to another and changes speed. When light enters a denser medium (e.g. from air to glass), it slows down and bends towards the normal; when it enters a less dense medium, it bends away from the normal.
当光从一种介质进入另一种介质并改变速度时，发生折射。光进入光密介质（如从空气到玻璃）时，速度减慢并向法线偏折；进入光疏介质时，则偏离法线。
White light is composed of a spectrum of colours. A prism can disperse white light into its component colours: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). This is called dispersion.
白光由一系列颜色组成。棱镜可将白光色散为红、橙、黄、绿、蓝、靛、紫（ROYGBIV），这称为色散。
Colour filters work by absorbing certain frequencies of light and transmitting others. A red filter transmits only red light and absorbs the other colours. The colour of an object depends on which colours it reflects; a red object reflects red light and absorbs the rest.
滤色镜通过吸收特定频率的光而让其他光透过。红色滤光片只透过红光，吸收其他颜色。物体的颜色取决于它反射哪种颜色；红色物体反射红光，吸收其他色光。
6. Electricity | 电学
Electric current is the flow of electric charge (usually electrons) around a circuit. It is measured in amperes (A) using an ammeter connected in series. Conventional current flows from the positive to the negative terminal of a cell.
电流是电荷（通常是电子）在电路中的流动。电流的单位是安培 (A)，用串联在电路中的电流表测量。常规电流方向是从电池的正极流向负极。
Voltage (or potential difference) is the energy supplied to each coulomb of charge, measured in volts (V) using a voltmeter connected in parallel across a component. It is the 'push' that drives the current.
电压（或电势差）是提供给每库仑电荷的能量，单位是伏特 (V)，用并联在元件两端的电压表测量。电压是驱动电流的 "推力"。
Resistance is the opposition to the flow of current, measured in ohms (Ω). Conductors have low resistance, while insulators have very high resistance. The relationship between voltage, current and resistance for ohmic conductors is:
电阻是对电流的阻碍，单位是欧姆 (Ω)。导体的电阻低，绝缘体的电阻非常高。对于欧姆导体，电压、电流和电阻的关系为：
V = I × R
电压 = 电流 × 电阻
In a series circuit, the current is the same everywhere. The total voltage is shared between the components. If one component fails, the circuit is broken and all components stop working.
在串联电路中，各处电流相等。总电压在各元件之间分配。如果一个元件损坏，电路断开，所有元件停止工作。
In a parallel circuit, the voltage across each branch is the same as the supply voltage. The total current is the sum of the currents in all branches. If one branch fails, the other branches continue to work.
在并联电路中，各支路电压等于电源电压。总电流等于各支路电流之和。如果一条支路断开，其他支路继续工作。
Circuit symbols for common components include: cell, battery, bulb, switch, ammeter, voltmeter, fixed resistor, variable resistor, and fuse. Being able to draw and interpret circuit diagrams is an essential practical skill.
常见元件的电路符号包括：电池、电池组、灯泡、开关、电流表、电压表、固定电阻、可变电阻和保险丝。能够绘制并解读电路图是一项重要的实验技能。
7. Magnetism and Electromagnets | 磁与电磁铁
A magnet has two poles, north (N) and south (S). Like poles repel and unlike poles attract. The magnetic field is the region around a magnet where magnetic forces act, represented by field lines that go from north to south.
磁铁有两个极：北极 (N) 和南极 (S)。同名极相斥，异名极相吸。磁场是磁铁周围能够施加磁力的区域，用从北到南的磁感线表示。
The Earth behaves like a giant bar magnet, with its magnetic south pole near the geographic North Pole. This is why a compass needle (a tiny magnet) points north: the north-seeking pole of the compass is attracted to the Earth's magnetic south pole.
地球就像一个巨大的条形磁铁，地磁南极靠近地理北极。这就是指南针（小磁铁）总是指向北方的原理：指南针的指北极被地磁南极所吸引。
An electromagnet is created by wrapping a coil of wire around a soft iron core and passing an electric current through it. The magnetic field can be switched on and off, and its strength increased by increasing the current, adding more turns of wire, or inserting an iron core.
电磁铁由绕在软铁芯上的线圈通以电流制成。它的磁场可以开关，通过增大电流、增加线圈匝数或插入铁芯可增强其磁性。
Electromagnets are used in many devices: electric bells, relays, loudspeakers, and magnetic resonance imaging (MRI) scanners. In scrapyards, powerful electromagnets are used to lift and move heavy steel objects.
电磁铁广泛应用于电铃、继电器、扬声器和磁共振成像 (MRI) 扫描仪等设备。在废车场，强大的电磁铁用来吊起和搬动沉重的钢铁物件。
8. Particle Model of Matter | 物质的粒子模型
All matter is made of tiny particles that are constantly moving. The arrangement and motion of these particles determine the state of matter: solid, liquid, or gas.
所有物质都由不断运动的微小粒子组成。粒子的排列和运动决定了物质的状态：固态、液态或气态。
In solids, particles are closely packed in a regular pattern and vibrate in fixed positions. Solids have a fixed shape and volume.
在固体中，粒子紧密排列成规则结构，只在固定位置振动。固体有固定的形状和体积。
In liquids, particles are close together but can slide past each other, so liquids have a fixed volume but take the shape of their container.
在液体中，粒子彼此靠近但能相互滑动，因此液体有固定的体积，但形状随容器而变。
In gases, particles are far apart and move randomly at high speeds. Gases have no fixed shape or volume and can be compressed easily.
在气体中，粒子相距很远，高速随机运动。气体没有固定的形状和体积，容易被压缩。
Changes of state, such as melting, freezing, boiling, condensation, sublimation, and deposition, are physical changes. Mass is conserved during these changes. During a change of state, the temperature stays constant until the change is complete.
物态变化，如熔化、凝固、沸腾、冷凝、升华和凝华，都是物理变化。在这些变化中质量守恒。在物态变化过程中，温度保持不变直到变化完全结束。
Gas pressure is caused by gas particles colliding with the walls of their container. Increasing the temperature increases the kinetic energy of the particles, making them collide more frequently and with greater force, thus increasing the pressure.
气体压强是由气体粒子撞击容器壁引起的。升高温度会增加粒子的动能，使它们撞击更频繁、力度更大，从而增大压强。
9. Density and Pressure | 密度与压强
Density is the mass per unit volume of a substance. It is calculated using:
密度是物质单位体积的质量。其计算公式为：
density = mass ÷ volume
密度 = 质量 ÷ 体积
Density is measured in kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). The density of water is 1 g/cm³ or 1000 kg/m³.
密度的单位是千克每立方米 (kg/m³) 或克每立方厘米 (g/cm³)。水的密度是 1 g/cm³ 或 1000 kg/m³。
Objects with a density less than water will float; those with a higher density will sink. The particle arrangement affects density: solids are typically the densest, followed by liquids, then gases.
密度小于水的物体上浮，大于水的下沉。粒子排列影响密度：固体通常密度最大，其次是液体，气体最小。
Pressure is the force acting per unit area. It is calculated as:
压强是单位面积上受到的压力。其计算公式为：
pressure = force ÷ area
压强 = 压力 ÷ 面积
lied over a smaller area produces a higher pressure (e.g. sharp knife), while spreading force over a larger area reduces pressure (e.g. snowshoes).
压强的单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。同样的力作用在较小面积上产生较大压强（如锋利的刀），而增大受力面积可减小压强（如雪鞋）。
× g, where h is depth, d is density of the liquid, and g is gravitational field strength.
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