IB物理 力学 热学 波动 电磁 核物理 备考
IB Core Physics 是 IBDP 科学组的核心课程，涵盖力学、热物理、波动、电磁学、圆周运动、原子与核物理等多个模块。SL 学生需完成 150 小时教学，HL 学生则为 240 小时。本文系统梳理各模块核心考点、公式要领与考试技巧，助你高效备考。
IB Core Physics is the central science course in the IB Diploma Programme, spanning mechanics, thermal physics, waves, electricity and magnetism, circular motion, atomic and nuclear physics. SL students complete 150 teaching hours while HL students cover 240 hours. This article systematically reviews key topics, essential formulas, and exam strategies to help you prepare efficiently.
1. Measurements and Uncertainties 测量与不确定度
物理实验的第一步永远是精确测量。IB 物理要求学生掌握 SI 基本单位（千克 kg、米 m、秒 s、安培 A、开尔文 K、摩尔 mol、坎德拉 cd），并能熟练进行单位转换。误差分析中需区分系统误差（systematic error）和随机误差（random error）：系统误差导致准确度偏差，可通过校准仪器修正；随机误差影响精密度，需通过多次测量取平均值减小。
Every physics experiment begins with accurate measurement. IB Physics requires mastery of the seven SI base units: kilogram (kg), metre (m), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). Students must distinguish between systematic errors, which shift accuracy and can be corrected by instrument calibration, and random errors, which affect precision and are reduced by repeated measurements and averaging.
不确定度（uncertainty）的计算是 Paper 3 的常考点：绝对不确定度为测量值加减范围，相对不确定度 = 绝对不确定度 / 测量值 x 100%。两个测量值加减时绝对不确定度相加，乘除时相对不确定度相加。矢量（vector）与标量（scalar）的区分也是基础：矢量有大小和方向（如位移、速度、力），标量仅有大小（如路程、速率、质量）。
Uncertainty calculations appear frequently in Paper 3. Absolute uncertainty is the plus-minus range of a measurement, while relative uncertainty equals absolute uncertainty divided by the measured value times 100%. When adding or subtracting two quantities, absolute uncertainties add; when multiplying or dividing, relative uncertainties add. Vector and scalar distinctions are also foundational: vectors carry both magnitude and direction (displacement, velocity, force), while scalars have magnitude only (distance, speed, mass).
2. Mechanics 力学
力学是 IB 物理分数占比最高的模块，涵盖运动学（kinematics）、牛顿定律、动量与冲量、功与能量四大核心。运动学中，匀加速直线运动四大公式（suvat equations）是必考内容：v = u + at, s = ut + 1/2 at^2, v^2 = u^2 + 2as, s = (u+v)t/2。注意符号约定：向上为正时，重力加速度 g = -9.81 m/s^2。
Mechanics carries the heaviest weight in IB Physics, covering kinematics, Newton's laws, momentum and impulse, work and energy. The four suvat equations for uniform acceleration are exam essentials: v = u + at, s = ut + 1/2 at^2, v^2 = u^2 + 2as, s = (u+v)t/2. Remember sign conventions: with upward as positive, gravitational acceleration g = -9.81 m/s^2.
牛顿三定律是理解力与运动关系的基石。第一定律（惯性定律）描述物体在合外力为零时保持静止或匀速直线运动；第二定律 F = ma 是最重要的定量公式；第三定律（作用力与反作用力）强调力总是成对出现，大小相等方向相反，作用在不同物体上。自由体图（free-body diagram）的绘制是考试中的高频技能点。
Newton's three laws form the bedrock of force-motion analysis. The first law describes inertia: objects maintain rest or uniform motion when net external force is zero. The second law F = ma is the most important quantitative relationship. The third law reminds us that forces always come in equal-and-opposite pairs acting on different bodies. Free-body diagram construction is a high-frequency exam skill.
动量守恒（conservation of momentum）在碰撞与爆炸问题中至关重要。p = mv，合外力为零时总动量守恒。弹性碰撞（elastic collision）动能也守恒，非弹性碰撞（inelastic collision）则部分动能转化为内能。冲量（impulse）FΔt = Δp 表示力随时间的累积效应，常用于解释安全气囊、缓冲垫等设计的物理原理。
Conservation of momentum is critical in collision and explosion problems. p = mv; total momentum is conserved when net external force is zero. In elastic collisions kinetic energy is also conserved, while inelastic collisions convert some kinetic energy into internal energy. Impulse, FΔt = Δp, represents the cumulative effect of force over time and explains the physics behind airbag and cushion designs.
功（work）和能量是力学的另一大支柱。功 W = Fs cosθ，只有力在位移方向的分量做功。动能 Ek = 1/2 mv^2，重力势能 Ep = mgh，弹性势能 Ep = 1/2 kx^2。功率 P = W/t = Fv。能量守恒（conservation of energy）是万能工具，许多复杂问题可通过分析能量转化轻松求解。效率（efficiency）= 有用输出 / 总输入 x 100%。
Work and energy complete the mechanics toolkit. Work W = Fs cosθ, only the force component parallel to displacement does work. Kinetic energy Ek = 1/2 mv^2, gravitational potential energy Ep = mgh, elastic potential energy Ep = 1/2 kx^2. Power P = W/t = Fv. Energy conservation is the universal tool; many complex problems yield to energy analysis. Efficiency = useful output / total input x 100%.
3. Thermal Physics 热物理
热物理研究温度、热量与物质状态变化。温度是分子平均动能的量度；热量是因温差而传递的能量。比热容（specific heat capacity）c 定义为 1 kg 物质升温 1 K 所需热量：Q = mcΔT。水的比热容高达 4200 J/(kg·K)，这是海洋调节气候的物理基础。比潜热（specific latent heat）L 描述相变时单位质量吸收或释放的热量：Q = mL。
Thermal physics studies temperature, heat, and changes of state. Temperature measures average molecular kinetic energy; heat is energy transferred due to temperature difference. Specific heat capacity c is the energy to raise 1 kg by 1 K: Q = mcΔT. Water's exceptionally high value of 4200 J/(kg·K) is the physical basis for oceanic climate regulation. Specific latent heat L describes energy per unit mass during phase change: Q = mL.
理想气体定律是 HL 学生的核心考点。波义耳定律（Boyle's Law）表明恒温下 pV = 常数；查理定律（Charles' Law）恒压下 V/T = 常数；盖-吕萨克定律（Gay-Lussac's Law）恒容下 p/T = 常数。三者综合为理想气体状态方程 pV = nRT，其中 R = 8.31 J/(mol·K)。阿伏伽德罗常数 NA = 6.02 x 10^23 mol^{-1} 连接宏观与微观世界。
Ideal gas laws are core HL territory. Boyle's Law: pV = constant at constant temperature. Charles' Law: V/T = constant at constant pressure. Gay-Lussac's Law: p/T = constant at constant volume. Together they form the ideal gas equation pV = nRT, where R = 8.31 J/(mol·K). Avogadro's number NA = 6.02 x 10^23 mol^{-1} bridges the macroscopic and microscopic worlds.
4. Waves 波动
波是能量传播的方式，分为横波（transverse wave）和纵波（longitudinal wave）。横波中振动方向垂直于传播方向（如光、水波），纵波中振动方向平行于传播方向（如声波）。波的基本参数：振幅 A、波长 λ、频率 f、周期 T = 1/f、波速 v = fλ。波的叠加原理（superposition）是理解干涉和驻波的基础。
Waves transmit energy and divide into transverse (vibration perpendicular to propagation, e.g. light and water waves) and longitudinal (vibration parallel to propagation, e.g. sound). Key parameters: amplitude A, wavelength λ, frequency f, period T = 1/f, wave speed v = fλ. The principle of superposition underpins understanding of interference and standing waves.
驻波（standing wave）在弦乐器和管乐器中至关重要。两端固定的弦上，基频 f1 = v/(2L)，各谐波为 fn = n f1。双缝干涉（double-slit interference）是光的波动性的经典证明：亮纹间距 Δy = λD/d，其中 D 为缝到屏幕距离，d 为缝间距。单缝衍射（single-slit diffraction）中，第一暗纹出现在 sinθ = λ/a。
Standing waves are essential for string and wind instruments. For a string fixed at both ends, fundamental frequency f1 = v/(2L) and harmonics follow fn = n f1. Double-slit interference is the classic proof of light's wave nature: bright fringe spacing Δy = λD/d, where D is slit-to-screen distance and d is slit separation. In single-slit diffraction, the first dark fringe occurs at sinθ = λ/a.
5. Electricity and Magnetism 电磁学
电路分析是 IB 物理的又一核心。欧姆定律（Ohm's Law）V = IR 是基础，但注意仅适用于欧姆导体。电阻 R = ρL/A，串联电路中总电阻 R = R1 + R2 + ...，并联电路中 1/R = 1/R1 + 1/R2 + ...。基尔霍夫定律（Kirchhoff's Laws）是分析复杂电路的有力工具：节点电流代数和为零，回路电压升代数和等于电压降代数和。
Circuit analysis is another IB Physics cornerstone. Ohm's Law V = IR is fundamental but note it applies only to ohmic conductors. Resistance R = ρL/A. In series, R = R1 + R2 + ...; in parallel, 1/R = 1/R1 + 1/R2 + ... . Kirchhoff's Laws powerfully analyze complex circuits: algebraic sum of currents at a junction equals zero, and algebraic sum of voltage rises equals sum of voltage drops around any closed loop.
电功率 P = IV = I^2 R = V^2/R。电动势（emf）是电源开路时的端电压，而路端电压（terminal p.d.）在有电流时因内阻压降而减小：V = ε - Ir。电磁感应（electromagnetic induction）中，法拉第定律 ε = -N ΔΦ/Δt 是关键，楞次定律决定了感应电流的方向。右手定则（Fleming's right-hand rule）是 HL 内容中判断运动导体感应电流方向的标准方法。
Electric power P = IV = I^2 R = V^2/R. Electromotive force (emf) is the open-circuit terminal voltage; under load, terminal p.d. drops due to internal resistance: V = ε - Ir. In electromagnetic induction, Faraday's Law ε = -N ΔΦ/Δt is key and Lenz's Law determines induced current direction. Fleming's right-hand rule is the standard HL method for finding induced current direction in a moving conductor.
6. Circular Motion and Gravitation 圆周运动与引力
匀速圆周运动中，虽然速率恒定但速度方向不断变化，故存在向心加速度 a = v^2/r = ω^2 r。向心力 F = mv^2/r = mω^2 r，它不是一种新的力，而是由拉力、重力、摩擦力等的合力提供。角速度 ω = 2π/T = 2πf，线速度 v = ωr。考试中常考汽车过拱桥、过山车最高点、圆锥摆等经典场景。
In uniform circular motion, speed is constant but velocity direction changes continuously, producing centripetal acceleration a = v^2/r = ω^2 r. Centripetal force F = mv^2/r = mω^2 r is not a new force type; it is the net resultant of tension, gravity, friction, etc. Angular velocity ω = 2π/T = 2πf, linear speed v = ωr. Classic exam scenarios include cars on arched bridges, roller-coaster peaks, and conical pendulums.
牛顿万有引力定律 F = GMm/r^2 统一了地面和天体的引力规律。引力场强度 g = F/m = GM/r^2，在地球表面约 9.81 N/kg。开普勒三定律（Kepler's Laws）描述行星运动：椭圆轨道、面积速度相等、T^2 与 r^3 成正比。卫星轨道、地球同步卫星（geostationary satellite）的高度计算是典型应用题。
Newton's law of gravitation F = GMm/r^2 unifies terrestrial and celestial gravity. Gravitational field strength g = F/m = GM/r^2, approximately 9.81 N/kg at Earth's surface. Kepler's three laws describe planetary motion: elliptical orbits, equal area in equal time, and T^2 proportional to r^3. Satellite orbits and geostationary satellite altitude calculations are classic application problems.
7. Atomic, Nuclear and Particle Physics 原子核与粒子物理
原子结构从卢瑟福散射实验（Rutherford scattering）到玻尔模型（Bohr model）再到量子力学描述，是 IB 物理的重要知识链。光电效应（photoelectric effect）证明了光的粒子性：光子能量 E = hf，逸出功 Φ 是电子逸出金属表面所需的最小能量。截止频率 f0 = Φ/h。爱因斯坦光电方程：hf = Φ + Ek_{max}。
Atomic structure from Rutherford scattering to the Bohr model to quantum mechanical descriptions forms a key knowledge chain in IB Physics. The photoelectric effect proved light's particle nature: photon energy E = hf, work function Φ is the minimum energy for electron emission. Threshold frequency f0 = Φ/h. Einstein's photoelectric equation: hf = Φ + Ek_{max}.
核物理中，三种放射性衰变需牢记：α 衰变（氦核，原子序数减 2 质量数减 4），β- 衰变（电子，原子序数加 1），β+ 衰变（正电子，原子序数减 1），γ 衰变（光子，能量变化无核素转换）。半衰期（half-life）公式 N = N0 (1/2)^(t/T_{1/2})。爱因斯坦质能方程 E = mc^2 解释了核反应中的质量亏损与能量释放。
In nuclear physics, memorise three decay types: alpha decay (helium nucleus, atomic number down 2, mass number down 4), beta-minus decay (electron, atomic number up 1), beta-plus decay (positron, atomic number down 1), and gamma decay (photon emission, no nuclear transmutation). Half-life formula: N = N0 (1/2)^(t/T_{1/2}). Einstein's mass-energy equation E = mc^2 explains mass defect and energy release in nuclear reactions.
8. IB 物理备考策略 Exam Strategy
Paper 1 选择题 MCQ
SL 30题 HL 40题，每题约 1.5 分钟。先做有把握的题，标记不确定的回头再啃。排除法是增强利器：排除明显错误选项，即使不确定也能提高正确率。单位检查（dimensional analysis）能快速排除单位不匹配的选项。
SL: 30 Q, HL: 40 Q, ~1.5 min each. Attempt all confident questions first, mark the uncertain ones. Elimination is powerful: discard obviously wrong options. Dimensional analysis can quickly rule out unit-mismatched choices.
Paper 2 简答计算 Short Answer
分值最高的试卷，考查知识深度与应用能力。写清已知量、未知量和所用公式，步骤分比最终答案更重要。即使算不出最终结果，列出正确公式也有分。Data-based questions 需仔细读图，从图表直接提取信息。
The highest-weighted paper tests depth and application. List known quantities, unknowns, and formulas; method marks outweigh final answers. Even without the final value, correct formulas earn marks. For data-based questions, extract information directly from graphs and tables.
Paper 3 实验与选修
Section A 考数据分析与实验技能：读不确定度、画最佳拟合线（best-fit line）、计算斜率与截距。Section B 考选修模块。标注坐标轴、合理选择比例尺、用误差棒（error bars）标出不确定度。
Section A tests data analysis and experimental skills: reading uncertainties, drawing best-fit lines, calculating slope and intercept. Section B covers the option topic. Label axes, choose sensible scales, use error bars to show uncertainties.
⚠️ 常见失分陷阱 Common Pitfalls
1. 单位遗忘：所有计算题最后必须带上单位，漏写单位常扣 1 分。Always include units in final answers; missing them costs 1 mark.
2. 有效数字：最终答案的有效数字应匹配题目中数据的最小有效数字位数。Match significant figures to the least precise value given in the question.
3. 方向与符号：矢量问题缺少方向描述只给一半分。Vector answers without direction earn only half marks.
4. 定义不精确：IB 评分标准对物理定义用词要求极高，背熟教材标准定义。IB mark schemes demand precise wording for definitions; memorise the textbook standard versions.
5. 画图潦草：射线图、电路图、自由体图必须用尺规清晰绘制。Ray diagrams, circuit diagrams, and free-body diagrams must be drawn neatly with a ruler.
9. 备考时间规划 Study Timeline
第1-2月 Month 1-2
系统梳理所有 Topic 知识点，配合课本完成章节习题。建立个人公式手册，按模块整理公式与适用条件。
Systematically cover all topics with textbook chapter questions. Build a personal formula handbook organised by module with applicability conditions.
第3月 Month 3
专项刷真题（past papers），按 Topic 分类练习。重点关注 Paper 2 的计算推导和 Paper 3 的数据分析。
Topic-focused past paper practice. Prioritise Paper 2 calculations and derivations plus Paper 3 data analysis.
第4月 Month 4
整套模考训练，严格计时。复盘错题，归纳错误类型。重点关注定义题、解释题的标准答案表述。
Full timed mock exams. Review errors and categorise mistake types. Focus on standard answer phrasing for definition and explanation questions.
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