📚 Mastering Edexcel IAL Physics Unit 1 & 2 | 掌握爱德思IAL物理单元1与2
This comprehensive revision guide covers all core topics from Edexcel International A-Level Physics Unit 1 (Mechanics and Materials) and Unit 2 (Waves and Electricity). Every concept is paired with clear explanations in both English and Chinese to strengthen your understanding and examination skills. From SUVAT equations and material deformation to wave interference and circuit calculations, you will find essential theory, formulae, and exam-style tips right here.
这份综合性复习指南涵盖了爱德思国际A-Level物理单元1（力学与材料）和单元2（波与电学）的所有核心主题。每个概念都配有清晰的中英文解释，以强化理解并提升应试能力。从SUVAT方程和材料形变到波的干涉以及电路计算，你将在此找到关键理论、公式和贴近考试的提示。
1. Kinematics | 运动学
Kinematics describes motion without considering its causes, using vector quantities such as displacement, velocity, and acceleration. The four SUVAT equations connect these for an object moving with constant acceleration in a straight line.
运动学在不考虑运动原因的情况下描述运动，使用位移、速度和加速度等矢量。对于直线匀加速运动的物体，四个SUVAT方程将这些量联系起来。
v = u + at
s = ut + ½at²
v² = u² + 2as
s = ½(u + v)t
In these equations, u is initial velocity, v is final velocity, a is acceleration, t is time, and s is displacement. Remember to choose a consistent positive direction when assigning signs to vectors.
在这些方程中，u为初速度，v为末速度，a为加速度，t为时间，s为位移。为矢量赋予符号时，务必选定一个一致的正方向。
Displacement–time and velocity–time graphs reveal motion details: gradient of s–t graph gives velocity, gradient of v–t graph gives acceleration, and area under v–t graph gives displacement. For free-fall motion, the acceleration due to gravity g is taken as 9.81 m s⁻² near Earth's surface.
位移‑时间图和速度‑时间图揭示运动细节：s‑t图的斜率给出速度，v‑t图的斜率给出加速度，v‑t图下的面积给出位移。在自由落体运动中，地球表面附近的重力加速度 g 取为 9.81 m s⁻²。
2. Forces and Newton's Laws | 力与牛顿定律
Newton's three laws govern how forces affect motion. The first law states that an object remains at rest or in uniform motion unless a resultant force acts on it. The second law links resultant force, mass and acceleration: Fresultant = ma. The third law explains that forces occur in equal and opposite pairs acting on different bodies.
牛顿三定律支配着力如何影响运动。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。第二定律将合力、质量和加速度联系起来：F合 = ma。第三定律说明力以大小相等、方向相反的成对形式作用在不同物体上。
Weight is the gravitational force acting on a mass: W = mg. The centre of gravity is the point where the entire weight appears to act. Resolving forces into perpendicular components using trigonometry is essential for analysing objects on inclined planes or in equilibrium.
重量是作用在质量上的引力：W = mg。重心是整个重量的作用点。利用三角函数将力分解为相互垂直的分量，对于分析斜面上或处于平衡状态的物体至关重要。
stance from the pivot. Taking moments about a suitable point often simplifies the calculation of unknown forces.
对于处于平衡的刚体，合力和合力矩都必须为零。力矩等于力 × 到支点的垂直距离。选取合适的支点计算力矩，通常能简化未知力的求解。
3. Work, Energy and Power | 功、能与功率
Work is done when a force moves its point of application in the direction of the force: W = Fd cos θ, where θ is the angle between force and displacement. Energy is the capacity to do work; it exists in many forms, including kinetic energy KE = ½mv² and gravitational potential energy GPE = mgΔh.
当力的作用点沿力的方向移动时，力做功：W = Fd cos θ，其中 θ 为力与位移的夹角。能量是做功的本领，它以多种形式存在，包括动能 KE = ½mv² 和重力势能 GPE = mgΔh。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another. In a closed system, total energy remains constant. Efficiency is the ratio of useful output energy to total input energy.
能量守恒原理指出，能量不能被创造或消灭，只能从一种形式转化为另一种形式。在一个封闭系统中，总能量保持不变。效率等于有用输出能量与总输入能量之比。
Power is the rate of work done or energy transferred: P = W/t = Fv W = 1 J s⁻¹. In practical situations, resistive forces cause energy to dissipate as heat.
功率是做功或传递能量的快慢：恒力条件下 P = W/t = Fv。功率的单位为瓦特 (W)，1 W = 1 J s⁻¹。在实际情形中，阻力会导致能量以热的形式耗散。
4. Materials and Hooke's Law | 材料与胡克定律
Elastic materials return to their original shape when the deforming force is removed, provided the elastic limit is not exceeded. Hooke's law states that the extension x of a spring is directly proportional to the applied force F: F = kx, where k is the spring constant.
弹性材料在移除形变力后能恢复原状，前提是不超过弹性极限。胡克定律指出，弹簧的伸长量 x 与所施加的力 F 成正比：F = kx，其中 k 为劲度系数。
For tensile stress and strain, stress is defined as force per unit cross-sectional area: σ = F/A, and strain is the extension per unit original length: ε = ΔL/L. The Young modulus E is the ratio of tensile stress to tensile strain within the limit of proportionality: E = σ/ε. Its unit is pascal (Pa).
对于拉伸应力和应变，应力定义为每单位截面积上的力：σ = F/A，应变是单位原始长度的伸长量：ε = ΔL/L。杨氏模量 E 是在比例极限内拉应力与拉应变的比值：E = σ/ε，单位为帕斯卡 (Pa)。
Force–extension graphs distinguish elastic and plastic regions. The area under the graph represents work done (strain energy). Brittle materials break with little plastic deformation, while ductile materials undergo significant plastic flow before fracture.
力‑伸长量图能区分弹性和塑性区域。图下面积代表所做的功（应变能）。脆性材料几乎不发生塑性形变就断裂，而延性材料在断裂前会经历显著的塑性流动。
5. Fluids and Viscosity | 流体与粘度
Viscosity is a fluid's internal resistance to flow. In laminar flow, layers of fluid slide smoothly past one another with no mixing; in turbulent flow, eddy currents and chaotic motion occur. The pressure in a fluid at rest increases with depth: Δp = ρgΔh.
粘度是流体对流动的内在阻力。在层流中，流体层平滑地相互滑动而无混合；在湍流中则出现涡流和无序运动。静止流体的压强随深度增加：Δp = ρgΔh。
For a small sphere moving slowly through a fluid, Stokes' law gives the viscous drag force: F = 6πηrv, where η is the viscosity, r the radius, and v the velocity. An object falling through a fluid eventually reaches terminal velocity when the total drag plus upthrust balance the weight.
对于在流体中缓慢运动的小球，斯托克斯定律给出的粘性阻力为：F = 6πηrv，其中 η 为粘度，r 为半径，v 为速率。物体在流体中下落，当总阻力加上浮力与重力平衡时，即达到终极速度。
Upthrust equals the weight of fluid displaced (Archimedes' principle). This is important for explaining floating, sinking and the terminal velocity of bubbles or droplets. Viscosity depends on temperature: for liquids it decreases with heating, whereas for gases it increases.
浮力等于排开流体的重量（阿基米德原理）。这对于解释漂浮、下沉以及气泡或液滴的终极速度非常重要。粘度与温度有关：液体加热时粘度减小，而气体加热时粘度增大。
6. Waves: Basics and Properties | 波的基础与性质
A wave transfers energy without transferring matter. In transverse waves (e.g. light, water waves), particle displacement is perpendicular to the direction of wave travel. In longitudinal waves (e.g. sound), particle displacement is parallel to the direction of travel.
波传递能量而不传递物质。在横波（如光波、水波）中，质点位移垂直于波的传播方向。在纵波（如声波）中，质点位移平行于传播方向。
avelength λ, frequency f, period T = 1/f, and wave speed v. The wave equation links these: v = fλ. Phase difference describes the fraction of a cycle by which one wave or particle leads or lags behind another.
波的关键参数包括位移、振幅 A、波长 λ、频率 f、周期 T = 1/f 和波速 v。波动方程将这些联系起来：v = fλ。相位差描述了一个波或粒子领先或落后于另一个波的周期分数。
| Transverse waves | Longitudinal waves |
| Displacement perpendicular to direction | Displacement parallel to direction |
| Electromagnetic waves, S-waves | Sound waves, P-waves |
Reflection, refraction and diffraction are characteristic wave behaviours. Diffraction is the spreading of waves around obstacles or through gaps; it is most noticeable when the gap size is comparable to the wavelength.
反射、折射和衍射是波的特征行为。衍射是波绕过障碍物或穿过狭缝时扩散的现象；当狭缝尺寸与波长相当时，衍射最明显。
7. Superposition and Standing Waves | 叠加与驻波
The principle of superposition states that when two or more waves meet, the resultant displacement is the vector sum of the individual displacements. Constructive interference occurs when waves are in phase, producing a larger amplitude; destructive interference occurs when waves are in antiphase, reducing amplitude.
叠加原理指出，当两列或多列波相遇时，合位移为各列波位移的矢量和。当波同相时发生相长干涉，产生更大振幅；当波反相时发生相消干涉，振幅减小。
For two coherent sources, a stable interference pattern is formed. Path difference determines the type of interference: a path difference of nλ gives constructive interference, while (n + ½)λ gives destructive interference, where n is an integer.
对于两个相干波源，会形成稳定的干涉图样。路程差决定了干涉类型：路程差为 nλ 时产生相长干涉，为 (n+½)λ 时产生相消干涉，其中 n 为整数。
and antinodes (maximum amplitude). On a stretched string fixed at both ends, the fundamental frequency corresponds to λ/2 = L, and harmonics are integer multiples of the fundamental.
当两列相同但方向相反的波叠加时，形成驻波。驻波具有波节（位移为零）和波腹（振幅最大）。在两端固定的弦上，基频对应于 λ/2 = L，谐频是基频的整数倍。
harmonics are present, and the fundamental wavelength relates to pipe length L by λ/4 = L.
对于两端开口的管，其谐波模式与弦相同。对于一端封闭的管，只存在奇次谐波，基频波长与管长 L 的关系为 λ/4 = L。
8. Electric Current and Potential Difference | 电流与电势差
Electric current I is the rate of flow of charge: I = ΔQ/Δt, measured in amperes (A). In metals, charge carriers are free electrons; in electrolytes, they are ions. Conventional current direction is opposite to electron flow.
电流 I 是电荷流动的速率：I = ΔQ/Δt，单位为安培 (A)。在金属中，载流子是自由电子；在电解质中，载流子是离子。常规电流方向与电子流动方向相反。
The potential difference (p.d.) between two points is the energy transferred per unit charge: V = W/Q. One volt is one joule per coulomb. The electromotive force (e.m.f.) of a source is the energy converted from chemical or other forms to electrical energy per unit charge delivered.
两点间的电势差 (p.d.) 是每单位电荷转移的能量：V = W/Q。1伏特等于1焦耳每库仑。电源的电动势 (e.m.f.) 是指每单位电荷所转化的从化学能或其他形式到电能的能量。
In a series circuit, current is the same everywhere; p.d. divides across components. In a parallel circuit, p.d. is the same across each branch, while currents add up at junctions. These conservation rules follow from charge and energy conservation.
在串联电路中，各处电流相同，电势差在各元件上分配。在并联电路中，各支路电压相同，而电流在节点处相加。这些守恒规则来源于电荷和能量守恒。
9. Resistance, Resistivity and Ohm's Law | 电阻、电阻率与欧姆定律
Resistance R is defined as R = V/I and measured in ohms (Ω). Ohm's law states that current through an ohmic conductor is directly proportional to the potential difference across it, provided temperature remains constant.
电阻 R 定义为 R = V/I，单位为欧姆 (Ω)。欧姆定律指出，在温度恒定的条件下，流过欧姆导体的电流与其两端电势差成正比。
The I–V characteristics reveal component behaviour: a fixed resistor gives a straight line through the origin; a filament lamp curves as resistance increases with temperature; a diode shows negligible current in reverse bias and exponential rise in forward bias.
I‑V 特性曲线揭示元件行为：定值电阻的图像为过原点的直线；灯丝灯泡因电阻随温度升高而增大呈现出曲线；二极管在反向偏压下电流极小，正向偏压时电流指数上升。
Resistivity ρ is an intrinsic material property: ρ = RA/L. The resistance of a wire increases with length and resistivity but decreases with cross-sectional area. Resistivity changes with temperature: for metals it increases, while for semiconductors it decreases.
电阻率 ρ 是材料的内禀属性：ρ = RA/L。导线的电阻随长度和电阻率增大而增大，但随截面积增大而减小。电阻率随温度变化：金属的电阻率升高，半导体的电阻率则降低。
10. Circuits, EMF and Internal Resistance | 电路、电动势与内阻
In a series circuit, total resistance is the sum of individual resistances: Rtotal = R₁ + R₂ + .... In parallel, the reciprocal rule applies: 1/Rtotal = 1/R₁ + 1/R₂ + .... Combining these rules allows analysis of complex networks.
串联电路的总电阻等于各电阻之和：R总 = R₁ + R₂ + ...。并联电路中适用倒数法则：1/R总 = 1/R₁ + 1/R₂ + ...。结合这些规则可以分析复杂网络。
The potential divider is a key circuit used to produce a fraction of the input voltage. The output voltage across resistor R₂ in series is Vout = (R₂/(R₁+R₂)) × Vin. This principle is widely used in sensor circuits, e.g. with LDRs or thermistors in one arm.
分压器是用于产生部分输入电压的关键电路。串联电阻 R₂ 两端的输出电压为 Vout = (R₂/(R₁+R₂)) × Vin。该原理广泛应用于传感器电路，例如将一个臂接入光敏电阻或热敏电阻。
Every real source has internal resistance r. The terminal potential difference V across the source decreases as current I increases: V = ε − Ir, where ε is e.m.f. The lost volts across the internal resistance is Ir. Measuring V for different I allows determination of ε and r from a linear graph.
每个实际电源都具有内阻 r。电源两端的路端电压 V 随电流 I 增大而减小：V = ε − Ir，其中 ε 为电动势。内阻上的电压降为 Ir。测量不同 I 下的 V，通过线性图线即可确定 ε 和 r。
Energy and power in circuits follow: P = IV = I²R = V²/R. Understanding these relationships is crucial for calculating heat dissipation and efficiency in electrical systems.
电路中的能量和功率遵循：P = IV = I²R = V²/R。理解这些关系对于计算电气系统中的热耗散和效率至关重要。
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