📚 Year 9 CAIE Physics: Core Concepts Overview | 9年级 CAIE 物理：核心知识点梳理
Year 9 CAIE Physics lays the groundwork for IGCSE by introducing fundamental ideas about measurement, motion, forces, energy, thermal physics, waves, electricity, and magnetism. This article organises the core concepts into clear, digestible sections to help you review essential theory, important equations, and typical applications. Each topic is presented in a bilingual format so you can strengthen your understanding in both English and Chinese.
9 年级 CAIE 物理为 IGCSE 课程奠定基础，介绍测量、运动、力、能量、热学、波、电学和磁学等基本概念。本文把核心知识点整理成清晰易懂的小节，帮助你复习重要的理论、关键公式和典型应用。每个主题都采用中英双语呈现，让你在两种语言中都能加深理解。
1. Physical Quantities and Measurement | 物理量与测量
All physical quantities can be divided into base quantities (like length, mass, time) and derived quantities (like speed, force, energy). In Year 9, you focus on length, mass, time, temperature, and volume, as well as common measuring instruments such as rulers, stopwatches, balances, and thermometers. Always record a measurement to the smallest division of the instrument and include the correct unit.
所有物理量都可分为基本量（如长度、质量、时间）和导出量（如速度、力、能量）。9 年级的重点是长度、质量、时间、温度和体积，以及常用的测量仪器，比如尺子、秒表、天平和温度计。读数时一定要读到仪器的最小刻度，并写上正确的单位。
- SI base units: metre (m), kilogram (kg), second (s), kelvin (K).
- 国际单位制基本单位：米 (m)、千克 (kg)、秒 (s)、开尔文 (K)。
- Prefixes: kilo (10³), centi (10⁻²), milli (10⁻³) help express very large or small numbers.
- 单位前缀：千 (10³)、厘 (10⁻²)、毫 (10⁻³) 用来表示很大或很小的数值。
- Volume may be measured using a measuring cylinder; read the bottom of the meniscus at eye level.
- 用量筒测量体积时，视线要与液面凹液面的最低处水平。
2. Speed, Velocity, and Acceleration | 速率、速度与加速度
Speed is the distance travelled per unit time, a scalar quantity. Velocity is speed in a given direction, a vector. Acceleration is the rate of change of velocity. The key equation for average speed is v = s / t, where v is speed, s is distance, t is time. Acceleration a = (v – u) / t, where u is initial velocity and v is final velocity.
速率是单位时间内的路程，是标量。速度是带有方向的速率，是矢量。加速度是速度变化的快慢。平均速率的核心公式是 v = s / t，其中 v 是速率，s 是路程，t 是时间。加速度 a = (v – u) / t，u 是初速度，v 是末速度。
v = s / t a = (v – u) / t
- Distance–time graphs: slope = speed; a horizontal line means stationary.
- 路程–时间图像：斜率 = 速率；水平线表示静止。
- Speed–time graphs: slope = acceleration; area under graph = distance travelled.
- 速度–时间图像：斜率 = 加速度；图像下的面积 = 走过的路程。
- Uniform acceleration: use the SUVAT equations only when acceleration is constant.
- 匀加速度：只有加速度恒定时才能使用 SUVAT 运动学方程。
3. Forces and Newton's Laws | 力与牛顿定律
A force is a push or pull that can change an object's shape or motion. Forces are vectors measured in newtons (N). Newton's First Law states that an object remains at rest or in uniform motion unless acted upon by a resultant force. The Second Law links resultant force F, mass m and acceleration a: F = m × a. The Third Law says every action has an equal and opposite reaction.
力是能改变物体形状或运动的推或拉。力是矢量，单位是牛顿 (N)。牛顿第一定律指出：除非受到合外力作用，否则物体会保持静止或匀速直线运动。第二定律把合外力 F、质量 m 和加速度 a 联系起来：F = m × a。第三定律：每一个作用力都有一个大小相等、方向相反的反作用力。
F = m × a
- Weight W = m × g, where g = 9.8 m/s² on Earth (≈10 m/s² for CAIE calculations).
- 重量 W = m × g，地球上 g = 9.8 m/s²（CAIE 计算常取 10 m/s²）。
- Friction opposes motion; air resistance increases with speed.
- 摩擦力阻碍运动；空气阻力随速度增大而增加。
- Resultant force is the vector sum of all forces; equilibrium means resultant force = 0 N.
- 合力是所有力的矢量和；平衡状态意味着合力 = 0 N。
4. Turning Effect of Forces (Moments) | 力的转动效应（力矩）
ce about a pivot is called the moment. Moment = force × perpendicular distance from pivot: M = F × d. The unit is newton metre (N m). For an object in rotational equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about the same pivot.
力绕支点的转动效应叫力矩。力矩 = 力 × 支点到力作用线的垂直距离：M = F × d。单位是牛顿·米 (N m)。物体处于转动平衡时，关于同一支点的顺时针力矩之和等于逆时针力矩之和。
M = F × d
- If a force is not perpendicular, use the perpendicular component of the force or the perpendicular distance.
- 如果力不垂直，需要取力的垂直分量或垂直距离。
- Centre of gravity: the point where the entire weight of an object appears to act.
- 重心：物体全部重量好像集中的那个点。
- A wider base and lower centre of gravity increase stability.
- 底面积越大、重心越低，物体越稳定。
5. Energy Stores and Transfers | 能量储存与转移
Energy is the capacity to do work, measured in joules (J). The main energy stores are kinetic, gravitational potential, elastic potential, thermal (internal), chemical, and nuclear. Energy can be transferred by forces (mechanical work), heating, radiation (light and sound), and electricity. The principle of conservation of energy states that energy can never be created or destroyed, only transferred or stored.
能量是做功的能力，单位是焦耳 (J)。主要的能量储存形式有：动能、重力势能、弹性势能、热（内）能、化学能和核能。能量可以通过力（机械功）、加热、辐射（光和声）以及电进行转移。能量守恒原理指出：能量既不能凭空产生，也不会凭空消失，只能转移或储存。
Eₖ = ½ m v² Eₚ = m g h
- Kinetic energy Eₖ = ½ × mass × (speed)².
- 动能 Eₖ = ½ × 质量 × (速率)²。
- Gravitational potential energy Eₚ = m g h, where h is height above a reference level.
- 重力势能 Eₚ = m g h，h 是相对于参考平面的高度。
- In an energy transfer, total energy input = useful energy output + wasted energy.
- 在能量转移中，总输入能量 = 有用输出能量 + 浪费的能量。
6. Work, Power, and Efficiency | 功、功率与效率
ject in the direction of the force. Work W = force × distance moved in direction of force: W = F × d. Power is the rate of doing work: P = W / t tts (W), where 1 W = 1 J/s. Efficiency = (useful output energy / total input energy) × 100%, or (useful power output / total power input) × 100%.
当力使物体沿力的方向移动时，就说力做了功。功 W = 力 × 沿力方向移动的距离：W = F × d。功率是做功的快慢：P = W / t，单位是瓦特 (W)，1 W = 1 J/s。效率 = (有用输出能量 / 总输入能量) × 100%，或 (有用输出功率 / 总输入功率) × 100%。
W = F × d P = W / t
- Efficiency is always less than 100% because of energy dissipated as thermal energy.
- 由于总有能量以热能形式耗散，效率始终小于 100%。
- Sankey diagrams show energy transfers, with arrow widths proportional to energy amounts.
- 桑基图用箭头宽度表示能量流动，宽度与能量大小成正比。
- 1 kilowatt-hour (kW h) = 3.6 × 10⁶ J, a unit of energy, not power.
- 1 千瓦时 (kW h) = 3.6 × 10⁶ J，是能量单位，不是功率单位。
7. Pressure | 压强
Pressure is the force acting per unit area: p = F / A m². Pressure in liquids depends on depth h, density ρ, and gravitational field strength g: p = ρ g h. The pressure at a point in a liquid acts equally in all directions.
压强是单位面积上的作用力：p = F / A。国际单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。液体压强取决于深度 h、密度 ρ 和重力场强度 g：p = ρ g h。液体中某一点的压强在各个方向上都相等。
p = F / A p = ρ g h
- For a gas, pressure is caused by particles colliding with the walls of the container.
- 气体压强由粒子撞击容器壁产生。
- Atmospheric pressure decreases with altitude; can be measured with a barometer.
- 大气压随高度增加而降低；可用气压计测量。
- Hydraulic systems use the principle that pressure is transmitted equally throughout an enclosed fluid.
- 液压系统利用密闭液体中压强等大传递的原理工作。
8. Thermal Physics: Heat and Temperature | 热学：热量与温度
Temperature is a measure of the average kinetic energy of particles, measured in degrees Celsius (°C) or kelvin (K). Absolute zero (−273 °C) is 0 K, where particles have minimum kinetic energy. Heat is the transfer of thermal energy from a hotter to a cooler region. Conduction, convection, and radiation are the three methods of heat transfer.
温度是粒子平均动能的量度，单位是摄氏度 (°C) 或开尔文 (K)。绝对零度 (−273 °C) 即 0 K，此时粒子动能最小。热量是热能从高温区域向低温区域的转移。传导、对流和辐射是三种热传递方式。
T (K) = θ (°C) + 273
- Conduction: occurs mainly in solids; metals are good conductors, non‑metals are insulators.
- 传导：主要发生在固体中；金属是良导体，非金属是绝缘体。
- Convection: occurs in fluids (liquids and gases); relies on density changes and circulation.
- 对流：发生在流体（液体和气体）中；依靠密度变化和循环流动。
- Radiation: transfer by infrared electromagnetic waves; does not need a medium. Dark, matt surfaces are good absorbers and emitters.
- 辐射：通过红外电磁波传递；不需要介质。深色粗糙表面是良好的吸收体和发射体。
- Evaporation causes cooling; the most energetic particles escape from a liquid’s surface.
- 蒸发引起冷却；动能最大的粒子从液体表面逸出。
9. Wave Properties | 波的性质
Waves transfer energy without transferring matter. In transverse waves, particles vibrate perpendicular to wave direction (e.g., water waves, light). In longitudinal waves, particles vibrate parallel to wave direction (e.g., sound). Key terms: wavelength λ, frequency f, period T, amplitude A, and wave speed v. The wave equation is v = f λ.
波传递能量而不传递物质。在横波中，粒子振动方向与波的传播方向垂直（例如水波、光波）。在纵波中，粒子振动方向与波的传播方向平行（例如声波）。关键术语：波长 λ、频率 f、周期 T、振幅 A 和波速 v。波动方程为 v = f λ。
v = f λ f = 1 / T
- Frequency f is the number of complete waves per second, unit hertz (Hz).
- 频率 f 是每秒完整波的个数，单位赫兹 (Hz)。
- Period T is the time for one complete wave, T = 1/f.
- 周期 T 是一个完整波所用的时间，T = 1/f。
- Reflection, refraction, and diffraction are wave behaviours; all obey the wave equation.
- 反射、折射和衍射都是波的行为；它们都遵守波动方程。
10. Light and the Electromagnetic Spectrum | 光与电磁波谱
omagnetic spectrum, in order of increasing frequency, is: radio waves, microwaves, infrared, visible light, ultraviolet, X‑ All EM waves travel at the same speed in a vacuum and differ in wavelength and frequency.
光是横电磁波，能在真空中以 c = 3.0 × 10⁸ m/s 传播。电磁波谱按频率递增的顺序是：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。所有电磁波在真空中速度相同，只是波长和频率不同。
- Reflection at a plane mirror: angle of incidence i = angle of reflection r.
- 平面镜反射：入射角 i = 反射角 r。
- Refraction: light bends when entering a different medium due to a change in speed.
- 折射：光进入不同介质时因速度变化而发生弯折。
- Dispersion: white light splits into a spectrum of colours because each colour has a different speed in glass.
- 色散：白光分解成彩色光谱，因为不同颜色的光在玻璃中速度不同。
- Lenses: converging (convex) lenses can form real or virtual images depending on object distance.
- 透镜：会聚（凸）透镜可根据物距形成实像或虚像。
11. Sound | 声音
Sound is a longitudinal wave produced by vibrating objects. It needs a medium to travel; sound cannot travel in a vacuum. The speed of sound in air is about 330–340 m/s. Sound waves can be reflected to produce echoes, and they can be refracted. Pitch relates to frequency; loudness relates to amplitude.
声音是由振动产生的纵波。它需要介质才能传播，不能在真空中传播。声音在空气中的速度约为 330–340 m/s。声波可以反射形成回声，也可以折射。音调与频率有关；响度与振幅有关。
- An oscilloscope can display sound waves, showing frequency and amplitude visually.
- 示波器可以显示声波波形，直观展示频率和振幅。
- Ultrasound refers to frequencies above 20 kHz, used in medical imaging and sonar.
- 超声波指频率高于 20 kHz 的声波，用于医学成像和声呐。
- Noise cancelling headphones use destructive interference to reduce unwanted sound.
- 降噪耳机利用相消干涉来减少不需要的声音。
12. Static Electricity and Simple Circuits | 静电与简单电路
riction transfers electrons from one material to another. An electric current is a flow of charge; conventional current flows from positive to negative, but electrons flow the opposite way. Current I = Q / t, where Q is charge and t is time.
电荷有两种：正电荷和负电荷。同种电荷相互排斥，异种电荷相互吸引。电荷的单位是库仑 (C)。摩擦起电使电子从一种材料转移到另一种材料。电流是电荷的流动；习惯电流方向是从正到负，但电子流动方向相反。电流 I = Q / t，Q 是电荷量，t 是时间。
I = Q / t
- Conductors allow charge to flow easily (e.g., metals); insulators do not (e.g., plastic).
- 导体容易让电荷流动（如金属）；绝缘体不容易（如塑料）。
- Simple circuits contain a cell, wires, and components such as lamps, resistors, and switches.
- 简单电路包含电池、导线和用电器，如灯泡、电阻和开关。
- In a series circuit, current is the same everywhere. In parallel circuits, current splits at junctions.
- 串联电路中电流处处相等；并联电路中电流在分支点分流。
- An ammeter measures current in series; a voltmeter measures potential difference in parallel.
- 电流表串联测量电流；电压表并联测量电势差。
13. Resistance, Ohm's Law, and Electrical Safety | 电阻、欧姆定律与用电安全
Resistance R measures how much a component opposes current. The unit is the ohm (Ω). Ohm’s Law states that for a metallic conductor at constant temperature, the current I is directly proportional to the potential difference V: V = I × R. Many components are non‑ohmic. Resistance of a wire increases with length, decreases with cross‑sectional area, and depends on material.
电阻 R 衡量元件对电流的阻碍程度，单位是欧姆 (Ω)。欧姆定律指出：对于温度不变的金属导体，电流 I 与电势差 V 成正比：V = I × R。许多元件是非欧姆性的。导线的电阻随长度增大而增大，随横截面积增大而减小，并与材料有关。
V = I × R
- Fuses and circuit breakers protect circuits by breaking the circuit if current is too high.
- 保险丝和断路器在电流过大时断开电路，起到保护作用。
- Earthing provides a safe path for current in case of a fault, preventing electric shock.
- 接地在发生故障时为电流提供安全通路，防止触电。
- Double insulation eliminates the need for an earth wire in some appliances.
- 双重绝缘使某些电器无需接地线。
- Electrical power P = I × V, energy E = I × V × t. Use of kilowatt‑hour for domestic energy.
- 电功率 P = I × V，电能 E = I × V × t。家庭用电常用千瓦时计量。
14. Magnetism and Electromagnetism | 磁学与电磁学
Magnets have north and south poles; like poles repel, unlike poles attract. Magnetic field lines show the direction of the field (north to south) and their spacing indicates strength. A current‑carrying wire produces a magnetic field around it; the direction can be found using the right‑hand grip rule. An electromagnet is a coil of wire (solenoid) with a soft iron core, which becomes magnetic when current flows.
磁体具有南极和北极；同名磁极相互排斥，异名磁极相互吸引。磁感线表示磁场方向（从北极指向南极），其疏密表示磁场强弱。载流导线周围会产生磁场；方向可用右手螺旋定则判断。电磁铁是带软铁芯的线圈（螺线管），通电时产生磁性。
- Increasing current, number of coil turns, or adding an iron core strengthens an electromagnet.
- 增大电流、增加线圈匝数或加入铁芯都能增强电磁铁。
- Magnetic effect of a current is used in relays, electric bells, and loudspeakers.
- 电流的磁效应应用于继电器、电铃和扬声器。
- A conductor moving in a magnetic field (or a changing magnetic field) induces a voltage – electromagnetic induction.
- 导体在磁场中运动（或变化的磁场）会产生感应电压——电磁感应。
- Permanent magnets are used in compasses, motors, and generators.
- 永磁体用于指南针、电动机和发电机。
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