📚 Year 12 CIE Physics: Core Concepts Revision | CIE物理核心知识点梳理
This article provides a concise yet comprehensive revision of the core topics for CIE AS-Level Physics (9702), covering physical quantities, mechanics, materials, waves, electricity, and particle physics. Each section presents essential definitions, laws, and equations in a clear, exam-focused manner.
本文为CIE AS物理（9702）核心知识点提供精简而全面的复习梳理，涵盖物理量、力学、材料、波动、电学和粒子物理。每一节都以考试重点为导向，清晰地列出关键定义、定律和方程。
1. Physical Quantities and Units | 物理量与单位
All physical quantities are expressed in terms of SI base units: kilogram (kg), metre (m), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). Derived units such as the newton (N) can be expressed as kg m s⁻². Equations must be homogeneous; every term must have the same base units. Prefixes are used to handle very large or very small numbers.
所有物理量都用国际单位制基本单位表示：千克(kg)、米(m)、秒(s)、安培(A)、开尔文(K)、摩尔(mol)和坎德拉(cd)。导出单位如牛顿(N)可表示为 kg m s⁻²。方程必须满足量纲一致性；每一项都具有相同的基本单位。使用前缀来处理极大或极小的数值。
| Prefix | Symbol | Factor |
|---|---|---|
| kilo | k | 10³ |
| mega | M | 10⁶ |
| giga | G | 10⁹ |
| tera | T | 10¹² |
| milli | m | 10⁻³ |
| micro | µ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
Vectors have both magnitude and direction (e.g., displacement, velocity, force); scalars have magnitude only (e.g., distance, speed, mass).
矢量既有大小又有方向（如位移、速度、力）；标量只有大小（如路程、速率、质量）。
2. Kinematics | 运动学
Displacement is a vector from the initial position to the final position. Velocity v is the rate of change of displacement: v = Δs/Δt. Acceleration a is the rate of change of velocity: a = Δv/Δt. For uniform acceleration in a straight line, the SUVAT equations apply:
位移是从初位置指向末位置的矢量。速度 v 是位移的变化率：v = Δs/Δt。加速度 a 是速度的变化率：a = Δv/Δt。对于直线匀加速运动，使用 SUVAT 方程：
v = u + at
s = ut + ½at²
s = ½(u+v)t
v² = u² + 2as
In free fall, the acceleration is the acceleration of free fall g = 9.81 m s⁻² downwards. Projectile motion is analysed by resolving velocity into independent horizontal (constant velocity) and vertical (constant acceleration g) components.
自由落体中，加速度为重力加速度 g = 9.81 m s⁻²，方向向下。抛体运动通过将速度分解为独立的水平分量（匀速）和竖直分量（匀加速度 g）来分析。
3. Dynamics | 动力学
Newton’s first law: an object remains at rest or in uniform motion unless acted upon by a net external force. Newton’s second law: the net force acting on an object equals the rate of change of its momentum, F = Δp/Δt. For constant mass, this simplifies to F = ma. Newton’s third law: forces occur in equal and opposite pairs.
牛顿第一定律：物体保持静止或匀速直线运动状态，除非受到净外力作用。牛顿第二定律：作用在物体上的净外力等于其动量的变化率，F = Δp/Δt。质量不变时，简化为 F = ma。牛顿第三定律：力总是成对出现，且大小相等、方向相反。
Momentum p = mv is a vector. Impulse = FΔt = Δp. In a closed system, total momentum is conserved. For collisions, elastic collisions conserve total kinetic energy; inelastic collisions do not.
动量 p = mv 是矢量。冲量 = FΔt = Δp。在封闭系统中，总动量守恒。碰撞中，弹性碰撞总动能守恒；非弹性碰撞则不守恒。
4. Forces, Density and Pressure | 力、密度和压强
Forces can be contact forces (normal reaction, friction, tension) or non-contact forces (gravitational, electric). The centre of gravity is the point where the entire weight of the object is considered to act. Density ρ = m/V. Pressure p = F/A.
力可以是接触力（法向反力、摩擦力、张力）或非接触力（引力、电力）。重心是整个物体的重量看似集中作用的那一点。密度 ρ = m/V。压强 p = F/A。
The pressure at a depth h in a fluid of density ρ is given by p = hρg. The upthrust on an object submerged in a fluid equals the weight of the fluid displaced (Archimedes’ principle).
在密度为 ρ 的流体中，深度 h 处的压强为 p = hρg。浸在流体中的物体所受的浮力等于其排开流体的重量（阿基米德原理）。
5. Work, Energy and Power | 功、能量和功率
Work done W = Fs cos θ represents the energy transferred by a force. Kinetic energy Eₖ = ½mv². Gravitational potential energy Eₚ = mgh. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another.
做功 W = Fs cos θ 表示力所传递的能量。动能 Eₖ = ½mv²。重力势能 Eₚ = mgh。能量守恒定律表明，能量不能创生也不能消灭，只能从一种形式转移为另一种形式。
Power P is the rate of doing work: P = ΔW/Δt. For a constant force moving at velocity v, P = Fv. Efficiency = (useful output power / input power) × 100%.
功率 P 是做功的速率：P = ΔW/Δt。对于以速度 v 运动的恒定力，P = Fv。效率 = (有用输出功率 / 输入功率) × 100%。
6. Deformation of Solids | 固体变形
Hooke’s law: the extension x of a spring is proportional to the applied force F, provided the elastic limit is not exceeded: F = kx, where k is the spring constant. Stress σ = F/A, strain ε = x/L (no units). The Young modulus E = σ/ε measures the stiffness of a material.
胡克定律：在不超过弹性限度时，弹簧的伸长量 x 与施加的力 F 成正比：F = kx，其中 k 为劲度系数。应力 σ = F/A，应变 ε = x/L（无单位）。杨氏模量 E = σ/ε 衡量材料的刚度。
Elastic potential energy stored in a deformed material is E = ½Fx = ½kx². Plastic deformation is permanent and occurs beyond the elastic limit.
变形材料储存的弹性势能为 E = ½Fx = ½kx²。塑性变形是不可逆的，发生在超过弹性极限之后。
7. Waves | 波
A progressive wave transfers energy without net movement of matter. In transverse waves, oscillations are perpendicular to the direction of energy propagation; in longitudinal waves, they are parallel. The wave speed v = fλ, where f is frequency and λ is wavelength.
行波传递能量而物质不发生净移动。横波中，振动方向与能量传播方向垂直；纵波中两者平行。波速 v = fλ，其中 f 是频率，λ 是波长。
The intensity I of a wave is proportional to the square of its amplitude. Electromagnetic waves travel at speed c = 3.00 × 10⁸ m s⁻¹ in a vacuum. Polarisation is a property exclusive to transverse waves and can be demonstrated with polarising filters.
波的强度 I 与其振幅的平方成正比。电磁波在真空中以 c = 3.00 × 10⁸ m s⁻¹ 的速度传播。偏振是横波独有的性质，可用偏振片演示。
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