📚 Edexcel IAL Physics Units 1, 3 & 6 Combined: Mechanics, Materials and Practical Skills | 爱德思IAL物理单元1、3、6综合：力学、材料与实验技能
This revision guide brings together the theory from Edexcel International A-Level Physics Unit 1 with the practical and analytical skills tested in Units 3 and 6. The combined approach helps you see how equations of motion, forces, energy and materials connect to experiment planning, uncertainty analysis and graph work.
本复习指南将爱德思国际A-Level物理单元1的理论与单元3和6考查的实验与分析技能整合在一起。这种综合方法能帮助你理解运动方程、力、能量和材料如何与实验设计、不确定度分析和图像处理联系起来。
1. Understanding the Combined Unit Approach | 理解单元综合考查的思路
Units 1, 3 and 6 are often taught separately, but the examiner expects you to use mechanics and materials theory to interpret practical data and assess experimental errors. Many Unit 1 questions include experimental scenarios, while Unit 3 and Unit 6 writing tasks require clear application of the theory.
单元1、3和6通常分开教学，但考官希望你运用力学与材料理论解释实验数据并评估实验误差。许多单元1题目包含实验情境，而单元3和单元6的书面任务也要求清晰运用理论。
Start your revision by listing the measurable quantities in mechanics: displacement, time, velocity, acceleration, mass, force, energy and extension. Then connect each quantity to a practical method you might use in the lab, such as a light gate for time or a pulley system for forces.
复习时先列出力学中可测量的物理量：位移、时间、速度、加速度、质量、力、能量和伸长量。然后把这些量与实验室可能用的方法联系起来，例如用光门测时间或用滑轮系统测力。
2. Core Mechanics: Motion and SUVAT | 核心力学：运动与运动学方程
For constant acceleration, the four SUVAT equations link displacement s, initial velocity u, final velocity v, acceleration a and time t. These equations are the backbone of Unit 1 motion questions and often appear in practical analysis.
对于匀加速运动，四个SUVAT方程将位移 s、初速度 u、末速度 v、加速度 a 和时间 t 联系起来。这些方程是单元1运动问题的基础，也常出现在实验分析中。
v = u + at
v² = u² + 2as
s = ut + ½at²
s = ½(u + v)t
Choose the equation that contains the unknown quantity and the three quantities you already know. In experiments, you often measure s and t, then calculate u, v or a; be prepared to rearrange any equation.
选择包含未知量和三个已知量的方程。实验中经常测量 s 和 t，然后计算 u、v 或 a；要能熟练移项变形任何方程。
- English: Always check that acceleration is constant before using SUVAT.
- 中文：使用SUVAT前必须确认加速度恒定。
- English: Use the sign convention consistently; choose the initial direction as positive.
- 中文：正方向要前后一致；通常选取初速度方向为正。
3. Newton's Laws and Free-body Diagrams | 牛顿定律与受力图
Newton' tral to mechanics problems. The third law is often misunderstood: the two forces act on different objects and are equal in magnitude but opposite in direction.
牛顿三定律解释了力如何改变运动。第二定律 F = ma 是力学问题的核心。第三定律常被误解：两个力作用在不同物体上，大小相等、方向相反。
F = ma
Draw a free-body diagram for every system: show weight, normal contact force, tension, friction and applied forces as arrows from a point. Resolve any force at an angle into horizontal and vertical components using F cos θ and F sin θ.
对每个系统画受力图：用从一点出发的箭头表示重力、支持力、张力、摩擦力和外加力。将斜向力分解为水平分量 F cos θ 和垂直分量 F sin θ。
. For accelerating systems, the resultant force in the direction of acceleration equals ma.
对于平衡状态，每个方向的合力必须为零：ΣF = 0。对于加速系统，加速度方向上的合力等于 ma。
4. Momentum, Impulse and Collisions | 动量、冲量与碰撞
Momentum p is the product of mass and velocity. The impulse of a force equals the change in momentum and is also the area under a force-time graph.
动量 p 等于质量与速度的乘积。力的冲量等于动量的变化，也等于力-时间图像下的面积。
p = mv
FΔt = Δp = mv – mu
In a closed system with no external resultant force, total momentum is conserved. Use conservation of momentum for collisions and explosions: total momentum before equals total momentum after.
在没有外部合力的封闭系统中，总动量守恒。碰撞和爆炸问题可使用动量守恒：碰撞前总动量等于碰撞后总动量。
For a perfectly elastic collision, kinetic energy is also conserved; in an inelastic collision, kinetic energy is transferred to other forms such as heat or sound. Unit 3 graph questions may ask you to find impulse from the area under a force-time curve.
完全弹性碰撞中动能也守恒；非弹性碰撞中动能转化为热、声等其他形式。单元3的图像题可能要求你通过力-时间曲线下的面积求冲量。
5. Work, Energy and Power | 功、能量与功率
on of the force. For a force F acting at angle θ to the displacement s, work W = Fs cos θ.
当力使其作用点沿力的方向移动时做功。若力 F 与位移 s 夹角为 θ，则功 W = Fs cos θ。
W = Fs cos θ
Kinetic energy, gravitational potential energy and power are key equations. Use energy methods when acceleration is not constant or when you want a quicker solution than resolving forces.
动能、重力势能和功率是关键公式。当加速度不恒定或想比受力分解更快解题时，可使用能量方法。
Eₖ = ½mv²
Eₚ = mgh
P = W/t = Fv
Always account for energy transfers, especially in practical tasks involving falling masses, springs or colliding trolleys. Identify useful output power and input power to comment on efficiency.
始终考虑能量转移，尤其是在涉及下落重物、弹簧或碰撞小车的实验任务中。区分有用输出功率与输入功率，以讨论效率。
6. Materials: Stress, Strain and Young Modulus | 材料：应力、应变与杨氏模量
Stress is force per unit cross-sectional area, and strain is extension per unit original length. Young modulus E is the ratio of stress to strain within the limit of proportionality.
应力是单位横截面积上的力，应变是单位原始长度的伸长量。杨氏模量 E 是比例极限内应力与应变的比值。
stress = F / A
strain = ΔL / L
E = stress / strain = FL / (AΔL)
For a typical linear-elastic material, a stress-strain graph starts as a straight line through the origin. The gradient of this initial linear section gives the Young modulus. Beyond the elastic limit, plastic deformation occurs and the material does not return to its original length.
对于典型的线弹性材料，应力-应变图起初是一条过原点的直线。初始线性段的斜率即为杨氏模量。超过弹性极限后发生塑性变形，材料不能恢复原长。
Remember that Young modulus is a property of the material, not the specific object, so two wires of the same material but different lengths and diameters have the same Young modulus. This is a common exam distinction.
记住杨氏模量是材料本身的属性，而不是特定物体的属性，因此同种材料、不同长度和直径的两根导线具有相同的杨氏模量。这是考试中常见的区分点。
7. Practical Skills: Variables, Uncertainties and Graphs | 实验技能：变量、不确定度与图像
For any experiment, identify the independent variable, dependent variable and control variables clearly. Use repeated readings for the dependent variable to reduce random uncertainty and calculate a mean.
任何实验都要清楚识别自变量、因变量和控制变量。对因变量进行重复测量以减少随机不确定度并计算平均值。
centage uncertainty is absolute uncertainty divided by the measured value, multiplied by 100%.
数字仪器的单次读数绝对不确定度通常为 ± 最小刻度值；模拟仪器通常为 ± 最小刻度的一半。百分不确定度等于绝对不确定度除以测量值再乘以100%。
When combining measurements, add absolute uncertainties for quantities added or subtracted, and add percentage uncertainties for quantities multiplied or divided. If a quantity is raised to a power, multiply the percentage uncertainty by that power.
组合测量时，加减运算用绝对不确定度相加；乘除运算用百分不确定度相加。如果物理量带有幂次，则将百分不确定度乘以该幂次。
Plot the dependent variable on the y-axis and the independent variable on the x-axis. Draw error bars where possible and use the line of best fit to find gradient and intercept. The gradient of a straight-line graph usually represents a useful physical quantity.
因变量画在 y 轴，自变量画在 x 轴。尽可能画出误差棒，并用最佳拟合线求斜率和截距。直线图像的斜率通常代表一个有意义的物理量。
8. Classic Required Experiments: Free Fall and Young Modulus | 经典必做实验：自由落体与杨氏模量
f you use s = ut + ½at² with u = 0, you can calculate g from measured height s and time t.
测量重力加速度 g 的一个标准实验是让一个小而密的球通过光门下落，或使用活板门和计时器。若使用 s = ut + ½at² 并令 u = 0，可通过测量高度 s 和时间 t 计算 g。
g = 2s / t²
Sources of uncertainty include reaction time, air resistance and parallax when measuring the drop height. Use a smaller time interval or an electronic timer to reduce these errors.
不确定度来源包括反应时间、空气阻力以及测量下落高度时的视差。可用更短的时间间隔或电子计时器减少这些误差。
To determine the Young modulus of a wire, measure the original length L, diameter d, applied mass m, and extension e. Use a vernier calliper and micrometer screw gauge for precision. Plot force F against extension ΔL; the gradient is F/ΔL, from which E can be found.
测定金属丝杨氏模量时，测量原始长度 L、直径 d、外加质量 m 和伸长量 e。使用游标卡尺和千分尺提高精度。绘制力 F 对伸长量 ΔL 的图像，斜率为 F/ΔL，由此可求出 E。
, and record the diameter in several places along the wire to check for uniform thickness.
始终用直径计算横截面积 A = πd²/4，并在金属丝不同位置多次测量直径以检查粗细是否均匀。
9. Evaluating Errors and Improving Methods | 误差分析与方法改进
Systematic errors affect every reading in the same direction, such as a zero error on a balance or a misaligned ruler. Random errors are unpredictable and can be reduced by repeated measurements.
系统误差使所有读数朝同一方向偏移，例如天平零点误差或尺子未对齐。随机误差不可预测，可以通过重复测量减少。
When evaluating an experiment, compare your result with an accepted value. Calculate the percentage difference: absolute difference divided by the accepted value, multiplied by 100%. If the percentage difference is much larger than the estimated percentage uncertainty, a systematic error or overlooked variable is likely present.
评估实验时，将结果与公认值进行比较。计算百分差：绝对差值除以公认值再乘以100%。如果百分差远大于估算的百分不确定度，可能存在系统误差或未控制的变量。
Suggest realistic improvements, such as using a digital timer rather than a stopwatch, clamping the ruler vertically, repeating with different masses, or using a longer fall distance. Always link the improvement to the error you want to reduce.
提出切实可行的改进，例如使用数字计时器代替秒表、将尺竖直固定、用不同质量重复实验或使用更长的下落距离。改进措施必须与要减小的误差对应。
10. Exam Tactics for Combined Questions | 综合题的考试策略
When a question mixes theory and practical analysis, begin by writing down the relevant equation and the quantities you know. Then convert units to SI and decide whether a vector sign convention is needed.
遇到理论与实验分析结合的问题时，先写出相关方程和已知量。然后将单位转换为国际单位制，并判断是否需要规定正方向。
Show substitutions clearly and give final answers to the same number of significant figures as the least precise measurement in the question. For graph questions, state the gradient units and explain what the gradient or intercept represents.
清楚展示代入过程，最终答案的有效数字位数应与题目中最不精确的测量值一致。图像题要写明斜率单位，并解释斜率或截距的物理意义。
In planning and evaluation questions, use the structure: identify variables, describe method, collect data, analyse graph, discuss uncertainties. Examiners award marks for clear order and justified choices.
在实验设计与评估题中，按以下结构作答：确定变量、描述方法、收集数据、分析图像、讨论不确定度。条理清晰、选择有据即可得分。
| Task | 任务 | Key equation | 关键公式 | Common error | 常见错误 |
|---|---|---|
| Free fall | 自由落体 | g = 2s / t² | Ignoring air resistance | 忽略空气阻力 |
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