📚 Year 9 CIE Physics: Core Concepts Review | Year 9 CIE 物理：核心知识点梳理
Welcome to your Year 9 CIE Physics revision guide. This resource covers the key topics you will encounter in the Cambridge Lower Secondary Science or introductory IGCSE Physics course. From motion and forces to energy, waves, electricity and magnetism, each section provides essential definitions, formulas and concepts with clear explanations in both English and Chinese to support bilingual learners.
欢迎使用 Year 9 CIE 物理复习指南。本文涵盖剑桥初中科学或 IGCSE 物理入门课程的核心主题。从运动与力到能量、波、电与磁，每个部分都提供了关键的定义、公式和概念，并以中英双语清晰解释，助力双语学习者。
1. Measurement and Units | 测量与单位
Physics relies on accurate measurements. The SI system uses base units: metre (m) for length, kilogram (kg) for mass, second (s) for time, kelvin (K) for temperature, and ampere (A) for electric current. Derived units include speed (m/s) and density (kg/m³). You must know how to use rulers, stopwatches and measuring cylinders, and understand the difference between precision and accuracy.
物理依赖精确的测量。国际单位制使用基本单位：米（m）表示长度，千克（kg）表示质量，秒（s）表示时间，开尔文（K）表示温度，安培（A）表示电流。导出单位包括速度（m/s）和密度（kg/m³）。你需要学会使用直尺、秒表和量筒，并理解精确度与准确度的区别。
When reading a scale, always record the measurement to the nearest division and estimate one extra digit if possible. Repeated measurements help reduce random errors. Systematic errors occur due to faulty equipment or incorrect zero setting. To calculate the average, sum the readings and divide by the number of readings.
读取刻度时，总是记录到最小分度值并尽可能估算一位数字。重复测量有助于减少随机误差。系统误差由仪器缺陷或错误的零位设置造成。计算平均值时，将读数相加再除以读数个数。
2. Motion and Speed | 运动与速度
Speed is the distance travelled per unit time. The formula is:
speed = distance / time
速度等于单位时间内通过的路程。公式为 速度 = 路程 / 时间，常用符号 v = d / t。单位是米每秒 (m/s)。
Average speed is found by dividing total distance by total time. If an object speeds up or slows down, you may calculate acceleration. Acceleration is the rate of change of velocity: a = (v − u) / t, where u is initial velocity and v is final velocity. The unit is m/s².
平均速度由总路程除以总时间求得。物体加速或减速时，可计算加速度。加速度是速度的变化率：a = (v − u) / t，其中 u 为初速度，v 为末速度，单位 m/s²。
Distance-time graphs show motion. A straight sloping line indicates constant speed; a horizontal line means the object is stationary. The gradient gives speed. Velocity-time graphs show acceleration: the area under the graph represents distance travelled.
距离-时间图显示运动。斜线表示匀速直线运动；水平线表示物体静止。斜率代表速度。速度-时间图显示加速度：图线下的面积代表通过的距离。
3. Forces and Effects | 力与作用效果
A force is a push or pull that can change an object's shape or motion. Forces are measured in newtons (N). Contact forces include friction and tension; non-contact forces include gravity, magnetic and electrostatic forces. Mass is the amount of matter (kg), while weight is the gravitational force on that mass: W = m × g, where g ≈ 10 N/kg on Earth.
力是能改变物体形状或运动的推或拉。力的单位是牛顿 (N)。接触力包括摩擦力和拉力；非接触力包括重力、磁力和静电力。质量是物质的多少（kg），而重量是作用在该质量上的重力：W = m × g，地球上 g ≈ 10 N/kg。
Resultant force determines the overall effect. Balanced forces keep an object stationary or moving at constant speed. Unbalanced forces cause acceleration according to Newton's second law: F = m × a. Friction opposes motion between surfaces—it can be useful (walking) or a problem (waste of energy).
合力决定总体效果。平衡力使物体静止或匀速运动。非平衡力根据牛顿第二定律产生加速度：F = m × a。摩擦力阻碍表面间的相对运动——它可能是有用的（行走）或带来麻烦（能量浪费）。
4. Energy Forms and Transfers | 能量形式与转化
Energy exists in many forms: kinetic, potential (gravitational and elastic), thermal, chemical, electrical, nuclear and light. Energy is measured in joules (J). The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed from one form to another.
能量有多种形式：动能、势能（重力势能和弹性势能）、热能、化学能、电能、核能和光能。能量的单位是焦耳 (J)。能量守恒定律指出，能量既不能被创造也不能被消灭，只能从一种形式转移或转化为另一种形式。
Gravitational potential energy depends on height: Eₚ = m × g × h. Kinetic energy depends on speed and mass: Eₖ = ½ × m × v². In many processes, energy is dissipated as thermal energy, reducing useful output. Efficiency is calculated as: efficiency = (useful energy output / total energy input) × 100%.
重力势能取决于高度：Eₚ = m × g × h。动能取决于速度和质量：Eₖ = ½ × m × v²。在许多过程中，能量会以热能形式耗散，减少有用输出。效率计算为：效率 = (有用能量输出 / 总能量输入) × 100%。
5. Thermal Physics | 热物理学
Heat is thermal energy in transfer. Temperature is measured in degrees Celsius (°C) or kelvin (K). Heat flows from hotter to cooler regions by conduction, convection and radiation. Conduction occurs mainly in solids via vibrating particles and free electrons. Convection happens in fluids (liquids and gases) where hotter, less dense fluid rises. Radiation does not need a medium—infrared waves can travel through a vacuum.
热是转移中的热能。温度以摄氏度 (°C) 或开尔文 (K) 计量。热量通过传导、对流和辐射从高温处流向低温处。传导主要发生在固体中，通过振动粒子和自由电子进行。对流发生在流体（液体和气体）中，较热、密度较小的流体上升。辐射不需要介质——红外波可以在真空中传播。
Good conductors include metals like copper. Insulators such as wood, plastic and trapped air reduce heat transfer. States of matter—solid, liquid, gas—depend on particle arrangement and movement. Melting and boiling are processes that require energy input (latent heat) without temperature change.
良导体包括铜等金属。绝缘体如木头、塑料和静止空气减少热传递。物质的三种状态——固态、液态、气态——取决于粒子的排列和运动。熔化和沸腾是需要能量输入（潜热）但温度不变的过程。
6. Waves and Sound | 波与声音
Waves transfer energy without transferring matter. There are two types: transverse waves (vibrations perpendicular to direction of travel, e.g., light, water waves) and longitudinal waves (vibrations parallel to direction of travel, e.g., sound). Key wave properties: amplitude, wavelength, frequency and wave speed.
波传递能量而不传递物质。有两种类型：横波（振动方向与传播方向垂直，例如光波、水波）和纵波（振动方向与传播方向平行，例如声波）。波的主要特性：振幅、波长、频率和波速。
Wave speed, frequency and wavelength are related by: v = f × λ, where v is speed (m/s), f is frequency (Hz), and λ (lambda) is wavelength (m). Sound is produced by vibrating objects and travels fastest in solids, then liquids, slowest in gases. The frequency of a sound determines its pitch; amplitude determines loudness.
波速、频率和波长的关系为：v = f × λ，式中 v 为速度 (m/s)，f 为频率 (Hz)，λ (lambda) 为波长 (m)。声音由振动物体产生，在固体中最快，液体次之，气体中最慢。声音的频率决定音调；振幅决定响度。
7. Light and Optics | 光与光学
dence = angle of reflection. These angles are measured from the normal, an imaginary line perpendicular to the surface. A plane mirror produces a virtual, upright, same-sized image that is laterally inverted.
光沿直线传播。当光照射到表面时，可以被反射、透射或吸收。反射定律：入射角等于反射角。这些角度从法线（垂直于表面的假想线）量起。平面镜产生正立、等大的虚像，且左右颠倒。
Refraction occurs when light passes from one medium to another at an angle, causing a change in speed and a bend. A lens uses refraction to converge (convex lens) or diverge (concave lens) light rays. White light consists of a spectrum of colours: red, orange, yellow, green, blue, indigo, violet (ROYGBIV). Dispersion can be shown with a prism.
当光以一定角度从一种介质进入另一种介质时，会发生折射，导致速度变化和光线弯曲。透镜利用折射来会聚（凸透镜）或发散（凹透镜）光线。白光由一系列颜色组成：红、橙、黄、绿、蓝、靛、紫 (ROYGBIV)。可以用棱镜演示色散。
8. Electricity and Circuits | 电与电路
Electric current is the flow of electric charge, measured in amperes (A). In a metal wire, current is a flow of electrons. Potential difference (voltage) is the energy transferred per unit charge, measured in volts (V). Resistance, measured in ohms (Ω), opposes the flow of current.
电流是电荷的流动，以安培 (A) 计量。在金属导线中，电流是电子的流动。电势差（电压）是每单位电荷转移的能量，以伏特 (V) 计量。电阻阻碍电流的流动，以欧姆 (Ω) 计量。
Ohm's law relates voltage, current and resistance: V = I × R. Components can be connected in series (single path, current same everywhere, voltage divides) or parallel (multiple paths, current splits, voltage same across each branch). Symbols for cell, battery, lamp, switch, resistor and ammeter must be recognised. An ammeter is connected in series, a voltmeter in parallel.
欧姆定律联系电压、电流和电阻：V = I × R。元件可以串联（单一路径，各处电流相等，电压分配）或并联（多条路径，电流分路，各支路电压相同）。必须认识电池、开关、灯泡、电阻和电流表的电路符号。电流表串联连接，电压表并联连接。
9. Magnetism and Electromagnetism | 磁与电磁
Magnets have north and south poles. Like poles repel; unlike poles attract. A magnetic field is a region where magnetic materials experience a force. Field lines run from north to south. Iron, nickel and cobalt are magnetic materials; a permanent magnet keeps its magnetism, while an induced magnet becomes magnetic only in a field.
磁铁有北极和南极。同名极相斥；异名极相吸。磁场是磁性材料受到作用力的区域。磁感线从北极指向南极。铁、镍、钴是磁性材料；永磁体保持磁性，而感应磁体仅在磁场中才表现出磁性。
An electric current produces a magnetic field around a wire. An electromagnet is a coil of wire (solenoid) around an iron core; its magnetism can be switched on and off and made stronger by increasing current or adding more turns. Electromagnets are used in relays, electric bells and lifting magnets.
电流在导线周围产生磁场。电磁铁是绕在铁芯上的线圈（螺线管）；其磁性可以开关，并通过增大电流或增加匝数来增强。电磁铁用于继电器、电铃和起重磁铁。
10. Matter and Density | 物质与密度
All matter is made of particles. The particle model explains the properties of solids (fixed shape, volume), liquids (fixed volume, take shape of container) and gases (fill container, can be compressed). Density is mass per unit volume: ρ = m / V, with units kg/m³ or g/cm³. To find density of an irregular solid, measure its mass with a balance and its volume by displacement of water in a measuring cylinder.
所有物质都由粒子组成。粒子模型解释了固体（形状、体积固定）、液体（体积固定，形状随容器）和气体（充满容器，可压缩）的性质。密度是单位体积的质量：ρ = m / V，单位 kg/m³ 或 g/cm³。测量不规则固体密度时，用天平测质量，用量筒排水法测体积。
Changes of state involve energy changes: melting, boiling, condensing and freezing. During a change of state, temperature remains constant while the substance absorbs or releases latent heat. Evaporation differs from boiling—it occurs only at the surface and can happen at any temperature.
物态变化涉及能量变化：熔化、沸腾、冷凝和凝固。在物态变化过程中，温度保持不变，物质吸收或释放潜热。蒸发与沸腾不同——只发生在液体表面，且可在任何温度下发生。
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