📚 IGCSE Physics: High-Frequency Topics Summary | IGCSE 物理：高频考点总结
Mastering IGCSE Physics requires focusing on the topics that appear most frequently in exams. This summary covers key concepts, formulas, and common pitfalls to help you revise efficiently.
掌握 IGCSE 物理的关键在于关注考试中最常出现的主题。本文总结了核心概念、公式和常见易错点，帮助你高效复习。
1. Kinematics | 运动学
Distance‑time graphs show how far an object travels over time; the gradient gives speed. Speed‑time graphs are vital: the gradient represents acceleration, and the area under the graph gives distance travelled.
距离‑时间图显示物体随时间移动的距离；斜率表示速度。速度‑时间图至关重要：斜率代表加速度，图线下的面积表示移动的距离。
Learn the four SUVAT equations for uniform acceleration, where v is final velocity, u initial velocity, a acceleration, t time, and s displacement.
要掌握匀加速运动的四个运动学方程，其中 v 为末速度，u 为初速度，a 为加速度，t 为时间，s 为位移。
v = u + at
v² = u² + 2as
s = ut + ½at²
s = ½(u + v)t
Always pay attention to signs: acceleration due to gravity g ≈ 9.8 m/s² downwards, which you may take as positive or negative depending on your direction convention.
务必注意正负号：重力加速度 g ≈ 9.8 m/s² 方向向下，根据你选定的正方向，可以取正值或负值。
2. Forces and Newton’s Laws | 力与牛顿定律
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 gives F = ma, linking force, mass and acceleration.
牛顿第一定律指出，除非受到合外力作用，物体将保持静止或匀速直线运动状态。第二定律给出 F = ma，建立了力、质量和加速度之间的关系。
Newton’s Third Law explains action–reaction pairs: if body A exerts a force on body B, then B exerts an equal and opposite force on A. These forces act on different objects and never cancel out in a free‑body diagram.
牛顿第三定律解释作用力与反作用力对：若物体 A 对 B 施加一个力，则 B 同时对 A 施加大小相等、方向相反的力。这两个力作用在不同物体上，在受力分析图上绝不会相互抵消。
Common forces include weight W = mg, friction, tension, normal reaction, and upthrust. Understanding free‑body diagrams is essential for solving multi‑force problems.
常见力包括重力 W = mg、摩擦力、张力、支持力和浮力。理解受力分析图对于解决多力问题至关重要。
For inclined planes, the weight component parallel to the slope is mg sin θ, and the component perpendicular to the slope is mg cos θ. Use these to find acceleration or normal contact force.
对于斜面，重力沿斜面方向的分量为 mg sin θ，垂直于斜面的分量为 mg cos θ。利用这些分量可求出加速度或支持力。
3. Energy, Work and Power | 能量、功和功率
Energy cannot be created or destroyed, only transferred. The principle of conservation of energy is tested in many contexts, such as a pendulum or a roller coaster. The main forms are kinetic energy Eₖ = ½mv², gravitational potential energy Eₚ = mgh, thermal, chemical, nuclear, and elastic (strain).
能量既不能创生也不能消灭，只能转化。能量守恒原理在许多情景中都会考查，如单摆或过山车。主要形式包括动能 Eₖ = ½mv²、重力势能 Eₚ = mgh、内能、化学能、核能和弹性势能。
Work done is given by W = Fd cos θ, where d is displacement and θ the angle between force and displacement. Power is the rate of doing work: P = W / t or P = Fv for constant velocity.
功的计算式为 W = Fd cos θ，其中 d 是位移，θ 是力与位移的夹角。功率是做功的速率：P = W / t 或匀速运动时 P = Fv。
Efficiency is the ratio of useful output energy to total input energy, often expressed as a percentage: Efficiency = (useful output / total input) × 100%. Sankey diagrams can illustrate energy transfers visually.
效率是指有用输出能量与总输入能量的比值，通常以百分比表示：效率 = (有用输出 / 总输入) × 100%。桑基图可以直观展示能量转化。
4. Waves | 波
Waves transfer energy without transferring matter. Transverse waves, such as light and water ripples, have oscillations perpendicular to the direction of energy transfer. Longitudinal waves, like sound, have oscillations parallel to the direction.
波传递能量而不传递物质。横波（如光和水波）的振动方向与能量传播方向垂直。纵波（如声波）的振动方向与传播方向平行。
The wave equation v = fλ links wave speed v, frequency f and wavelength λ. Remember to convert units: cm to m, kHz to Hz.
波动方程 v = fλ 将波速 v、频率 f 和波长 λ 联系起来。记住单位换算：厘米换算成米，千赫兹换算成赫兹。
Reflection follows the law of reflection: angle of incidence i equals angle of reflection r. Refraction occurs when waves change speed at a boundary; Snell’s Law is n = sin i / sin r, where n is the refractive index.
反射遵循反射定律：入射角 i 等于反射角 r。折射发生在波在界面改变速度时；斯涅耳定律为 n = sin i / sin r，其中 n 为折射率。
Total internal reflection occurs when light travels from a denser to a less dense medium at an angle greater than the critical angle c, where sin c = 1/n
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