AS AQA 物理 Unit 2 涵盖力学、材料学和波动三大模块，是许多学生备考中最头疼的部分。本文结合 2022 年 6 月真题，系统梳理高频考点和常见失分点，帮助同学们高效备考、精准提分。| Covers Mechanics, Materials & Waves. Key topics from June 2022 past paper.
一、力学中的矢量分解与受力分析 | Vector Resolution & Force Analysis
力学是 Unit 2 分值最高的模块，约占 40%。矢量分解和牛顿第二定律是必考内容。| Mechanics ~40% of marks. Vector resolution and F=ma guaranteed to appear.
2022 真题典型题：斜面上物体受力，需同时使用平行和垂直斜面的分解。关键公式：| Typical June 2022 question: resolving forces on inclined plane. Key equations:
平行斜面：F = mg sinθ − f = ma
垂直斜面：R = mg cosθ
常见失分点：混淆 sin/cos 的使用方向、遗漏摩擦力方向。摩擦力方向总与相对运动趋势相反。| Common errors: confusing sin vs cos, missing friction direction. Friction opposes relative motion.
牛顿第二定律与连接体问题 | Connected Particles
连接体问题考察整体法和隔离法的灵活切换。轻绳连接的物体加速度相同，先对整体求加速度，再隔离求张力。| Connected bodies share same acceleration. Find it for the system first, then isolate to find tension.
二、动量守恒与碰撞问题 | Conservation of Momentum & Collisions
动量守恒适用于所有孤立系统，无论碰撞是弹性还是非弹性。弹性碰撞中动能守恒，非弹性碰撞部分动能转化为热能或形变能。2022 真题考察小车碰撞的速度计算，需同时运用动量守恒和动能条件来判断碰撞类型，很多考生在此处失分。| Momentum conserved in isolated systems. Elastic collisions conserve KE; inelastic don't. June 2022: trolley collision question required both momentum and energy analysis.
动量-时间图面积 = 冲量，斜率 = 合力。几何理解可简化计算。| Area under p-t graph = impulse; gradient = resultant force.
三、应力、应变与杨氏模量 | Stress, Strain & Young Modulus
应力 = 力/面积，应变 = 伸长量/原长，杨氏模量 = 应力/应变。此关系仅在比例极限内成立，超出后材料将偏离胡克定律。2022 实验题：从力-伸长量图计算 E，注意 mm² → m² 单位转换，面积单位错误是最常见的扣分点。| Stress=F/A, strain=ΔL/L, E=stress/strain (within limit of proportionality). June 2022: calculate E from F-extension graph. Common pitfall: mm²→m² conversion.
弹性与塑性行为 | Elastic & Plastic Behaviour
弹性形变撤力后恢复原状，塑性形变产生永久形变。应力-应变曲线上的弹性极限和屈服点是区分两者的关键标志。脆性材料（如玻璃）在弹性极限处直接断裂，而韧性材料（如铜）则经历明显的塑性变形阶段后才断裂。| Elastic: returns to original shape. Plastic: permanent deformation. Brittle materials (glass) fracture at elastic limit; ductile materials (copper) undergo plastic deformation first.
四、波的叠加与干涉条件 | Wave Superposition & Interference
双缝干涉公式：w = λD/s。2022 真题：用激光和双缝测波长，分析 D 增大时条纹间距变化。w 与 D 成正比。| Young's double-slit: w=λD/s. June 2022: fringe spacing increases with D, w ∝ D.
相干光源与路径差 | Coherent Sources & Path Difference
干涉需相干光源（同频率、恒定相位差），激光是理想选择。路径差 = nλ 时相长干涉（亮纹），= (n+½)λ 时相消干涉（暗纹）。| Coherence: same frequency, constant phase difference. Constructive at nλ, destructive at (n+½)λ.
五、驻波与谐波频率 | Stationary Waves & Harmonics
驻波由两列同频反向波叠加形成，特征为节点和腹点。基频公式：f = (1/2L)√(T/μ)。第 n 次谐波 f = nf₀。2022 实验：改变张力验证 f ∝ √T，作 f-√T 图得过原点直线。| Stationary waves: nodes & antinodes. f=(1/2L)√(T/μ). Harmonics: f=nf₀. Verify f∝√T by plotting f vs √T.
六、折射定律与全反射 | Snell's Law & Total Internal Reflection
Snell 定律：n₁sinθ₁ = n₂sinθ₂。折射率 n = c/v。全反射条件：光密→光疏且入射角 > 临界角。sin C = 1/n。光纤利用全反射传输信号。| Snell's law: n₁sinθ₁=n₂sinθ₂. n=c/v. TIR: denser→rarer, angle>C. sin C=1/n. Optical fibres use TIR.
七、Unit 2 备考策略与评分要点 | Exam Strategy & Marking Tips
综合 2022 年评分报告，四点注意：| Key takeaways from 2022 examiners' report:
第一，定义题必须精确。"杨氏模量"定义须含"比例极限内"，缺此短语失分。| 1. Definitions must be precise — "Young modulus" needs "within limit of proportionality".
第二，计算展示完整步骤：公式代入→计算→单位，缺步扣分。| 2. Show full working: substitution→calculation→unit.
第三，实验描述如何减误差：游标卡尺测直径、重复取平均、从图线求梯度。| 3. Reduce uncertainty: vernier callipers, repeat readings, graph gradient.
第四，解释题用关键词。"干涉"需要"相干、路径差、相长/相消"等术语。| 4. Use key terms in explanations — "coherent, path difference, constructive/destructive" for interference.
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