Year 10 WJEC Engineering: Common Misconceptions and Correction Methods | WJEC 10年级工程：常见误区与纠正方法

📚 Year 10 WJEC Engineering: Common Misconceptions and Correction Methods | WJEC 10年级工程：常见误区与纠正方法

Engineering at Year 10 introduces fundamental concepts that underpin everything from structural analysis to electronics. However, many students carry forward persistent misconceptions that can hinder their progress. This article tackles the most common misunderstandings, explains the correct principles in simple terms, and shows you how to avoid losing marks in assessments. By addressing these errors head-on, you can build a more solid foundation for further study and practical problem-solving.

10年级工程学介绍了从结构分析到电子学的基础概念。然而，许多学生总是带着一些延续下来的错误观念，这会阻碍他们的进步。本文针对最常见的误区，用简单的语言解释正确的原理，并教你如何在考试中避免丢分。直面这些错误，你就能为深入学习和解决实际问题打下更扎实的基础。

1. Confusing Mass and Weight | 混淆质量与重量

Many students think mass and weight are interchangeable, but in engineering they are completely different quantities. Mass is the amount of matter in an object, measured in kilograms (kg), and does not change whether you are on Earth, the Moon, or in space. Weight is a force caused by gravity, measured in newtons (N), and depends on the gravitational field strength.

许多学生认为质量和重量可以互换，但在工程学中它们是截然不同的量。质量是物体所含物质的多少，单位为千克（kg），无论你在地球、月球还是太空都不会改变。重量是由重力产生的力，单位为牛顿（N），取决于重力场强度。

A common mistake is writing that a bridge pillar supports a load of 5000 kg. The correct engineering statement is that it supports a weight of 5000 N or a mass that exerts 5000 N of force. Always use the formula:

一个常见错误是写成桥墩支撑了5000 kg的荷载。正确的工程表述是支撑了5000 N的重量，或者支撑的质量产生了5000 N的力。请始终使用以下公式：

W = m × g (where g ≈ 9.8 N/kg on Earth)

When drawing free-body diagrams, show forces in newtons, never in kilograms. Remember: a scale measures your mass, but it actually reacts to your weight and converts it internally.

画自由体图时，力一定要用牛顿表示，绝不能用千克。记住：体重秤测的是你的质量，但它实际上是感受到你的重量然后在内部转换的。

2. Misunderstanding Stress and Strain | 误解应力与应变

Students often confuse stress with pressure or assume strain simply means deformation. Stress is defined as force per unit area within a material and is measured in pascals (Pa) or N/m². Strain is the ratio of extension to original length — it is dimensionless and has no units.

学生常常把应力与压强混淆，或者认为应变就是指形变。应力的定义是材料内部单位面积上的力，单位是帕斯卡（Pa）或N/m²。应变则是伸长量与原长之比——它是一个无量纲，没有单位。

A classic error is saying ‘the stress is 5 mm’. Stress is never a length; it is a force applied over an area. Strain can be small, such as 0.002, meaning a 2 m rod has extended by 4 mm. Remember the formulas:

一个经典错误是说“应力是5 mm”。应力绝不可能是长度；它是施加在面积上的力。应变可以很小，比如0.002，意味着一根2 m的杆伸长了4 mm。记住这两个公式：

σ = F / A (stress = force / cross-sectional area)

ε = ΔL / L₀ (strain = change in length / original length)

When interpreting tensile test graphs, note that Young’s modulus is the gradient of the linear part, not the peak force. A high Young’s modulus means the material is stiff, not necessarily strong.

在解读拉伸测试图时，注意杨氏模量是直线段的斜率，而不是最大力。杨氏模量高意味着材料刚性强，并不一定强度高。

3. Force Equilibrium and Free-Body Diagrams | 力平衡与自由体图

Many learners think that if an object is stationary, no forces are acting on it. In equilibrium, the net force is zero, but individual forces such as weight and the normal reaction still exist. Another error is drawing force arrows that do not originate from the correct point of application.

很多学习者认为物体静止就意味着没有力作用在它上面。在平衡状态下，合力为零，但个别力如重量和法向反作用力依然存在。另一个错误是画力箭头时没有从正确的作用点出发。

Every free-body diagram should isolate the body and show only external forces. A truss joint in equilibrium must satisfy:

每一幅自由体图都应该隔离该物体，并只画出外力。一个处于平衡的桁架节点必须满足：

ΣFₓ = 0 and ΣFᵧ = 0

Use arrows that are proportional in length to the magnitude of the forces. If a cable is in tension, the force arrow pulls away from the body; if a strut is in compression, the arrow pushes towards the body. Never forget to include the object’s weight acting downwards at its centre of gravity.

箭头的长度应与力的大小成比例。如果缆索受拉，力箭头应远离物体；如果支柱受压，箭头应指向物体。切勿忘记在重心处标出物体向下的重量。

4. Electrical Laws: Ohm’s Law Misapplications | 电学定律：欧姆定律的误用

A widespread misconception is that Ohm’s law (V = I × R) can be applied to every component under all conditions. Ohm’s law only holds for ohmic conductors at constant temperature; diodes, filament lamps, and thermistors are non-ohmic so their V-I graph is not a straight line.

一个普遍的错误观念是欧姆定律（V = I × R）在任何条件下都适用于所有元件。欧姆定律只对恒定温度下的欧姆导体成立；二极管、白炽灯和热敏电阻都是非欧姆元件，其电压-电流图不是直线。

Students also mistakenly think that resistance is fixed for a component. In reality, the resistance of a filament lamp increases as it heats up because the metal ions vibrate more, making it harder for electrons to flow. When calculating resistance, always use the voltage across the component and the current through it at that specific moment.

学生还错误地认为一个元件的电阻是固定的。实际上，白炽灯的电阻会随着温度升高而增大，因为金属离子振动加剧，电子流动更困难。计算电阻时，一定要使用该时刻元件两端的电压和流过它的电流。

R = V / I

Remember: an ohmic conductor has a constant resistance only if temperature remains unchanged. A graph of V against I for an ohmic resistor is a straight line through the origin; for a diode, it crosses at around 0.7 V and then rises steeply.

记住：只有温度保持不变时，欧姆导体才有恒定电阻。欧姆电阻的V-I图是一条过原点的直线；二极管则在约0.7 V处开启然后陡升。

5. Series vs. Parallel Circuits | 串联与并联电路区分不清

Some students believe that adding more resistors in series decreases total resistance — this is the opposite of the truth. In series, resistances add up (R_total = R₁ + R₂ + …), so total resistance always increases. In parallel, the total resistance is less than the smallest individual resistance because multiple paths are available for current.

有些学生以为在串联中增加更多电阻会降低总电阻——事实恰好相反。串联时，电阻相加（R_total = R₁ + R₂ + …），总电阻总是增大。并联时，总电阻小于最小的单个电阻，因为电流有多条路径。

Another frequent mistake is assuming the current is the same in all branches of a parallel circuit. Current splits at junctions, while voltage remains the same across each branch. Use these rules:

另一个常见错误是认为并联电路中所有分支的电流相同。电流在节点处分流，而各支路两端的电压相同。请使用以下规则：

Series: current same everywhere, voltage divides.

串联：各处电流相同，电压分配。
Parallel: voltage same across branches, current splits.

并联：各支路电压相同，电流分流。

When calculating total resistance for two parallel resistors, use the product-over-sum shortcut (R_total = (R₁ × R₂) / (R₁ + R₂)) only for two resistors. For more, you must use:

计算两个并联电阻的总电阻时，可以用乘积除以和（R_total = (R₁ × R₂) / (R₁ + R₂)），这只适用于两个电阻。更多电阻必须用：

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + …

6. Engineering Drawing Conventions: Orthographic Projection | 工程制图规范：正交投影

A regular error is confusing first-angle and third-angle projection. In first-angle, the view is placed on the opposite side from which it is seen; in third-angle, the view is placed on the same side. WJEC often expects third-angle projection, so check your specification.

一个常见错误是混淆第一角投影和第三角投影。第一角投影中，视图放在观察方向的对面；第三角投影中，视图放在观察方向的同侧。WJEC通常要求第三角投影，请检查考纲。

Students frequently omit hidden detail lines (dashed lines) or centre lines in orthographic drawings. A hidden edge must be shown as a thin dashed line; otherwise the drawing is incomplete. Dimensions should be placed outside the view and never on the object itself.

学生在正交图中经常遗漏隐藏细节线（虚线）或中心线。隐藏边必须用细虚线表示，否则图纸不完整。尺寸应标注在视图外部，绝不要直接标在物体轮廓上。

Always draw a 45° miter line to transfer dimensions between views in third-angle projection.

在第三角投影中，一定要画一条45°斜线来在视图之间转移尺寸。
Use a title block, scale, and correct line types: continuous thick for outlines, continuous thin for dimension lines, and dashed for hidden edges.

使用标题栏、比例尺和正确的线型：粗实线表示轮廓，细实线表示尺寸线，虚线表示隐藏边。

7. Material Properties: Hardness vs. Toughness | 材料性能：硬度与韧性

Many learners treat hardness and toughness as synonyms. Hardness is a material’s resistance to indentation or scratching; toughness is the ability to absorb energy and plastically deform without fracturing. A ceramic plate is hard but brittle, whereas a steel spring is tough.

很多学习者把硬度和韧性当作同义词。硬度是材料抵抗压入或刮擦的能力；韧性是材料吸收能量并发生塑性变形而不断裂的能力。陶瓷盘子硬而脆，钢弹簧则具有韧性。

Another confusion involves strength and stiffness. High strength means a large force is needed to break the material; high stiffness means it deforms very little under load. A glass fibre rod can be both strong and stiff, but not tough. When selecting materials for a task, consider the combination of properties needed:

另一个混淆涉及强度和刚度。高强度意味着需要很大的力才能使材料断裂；高刚度意味着它在载荷下变形很小。玻璃纤维杆可以既强又刚，但不韧。在为某项任务选材时，要考虑所需性能的组合：

Car body panels: good ductility and strength, moderate cost.

汽车车身板：良好的延展性和强度，成本适中。
Cutting tools: extremely hard, heat-resistant, but can be brittle.

切削工具：极度坚硬、耐热，但可以脆。
Safety helmets: tough, lightweight, and able to absorb impact energy.

安全头盔：韧性好、轻质，能吸收冲击能量。

8. The Design Process: Skipping Steps | 设计过程：跳过关键步骤

A common pitfall is jumping straight to building a prototype without adequate research, specification writing, or iterative sketching. The engineering design process is cyclical: define the problem → research → specify → generate ideas → develop solution → model/test → evaluate. Missing the specification stage often results in a product that does not meet the user’s needs.

一个常见陷阱是没有经过充分调研、编写规格书或迭代草图就直接跳入原型制作。工程设计过程是循环的：定义问题→调研→制定规格→生成方案→开发设计→建模/测试→评估。缺少规格制定阶段常常导致产品不满足用户需求。

Another mistake is failing to record design decisions. WJEC coursework demands a clear design log showing why you chose certain materials, manufacturing processes, or dimensions. Always link choices back to the specification. For example: ‘Aluminium was selected because it is lightweight (density 2700 kg/m³) and corrosion-resistant, meeting spec point 4.’

另一个错误是没有记录设计决策。WJEC课程作业要求清晰的设计日志，说明你为何选择了某些材料、制造工艺或尺寸。始终将选择与规格书关联。例如：“选用铝材是因为它轻质（密度2700 kg/m³）且耐腐蚀，符合规格第4条”。

Use iterative testing and refinement. If a cardboard model shows weakness at a joint, reinforce it and re-test — then document both the failure and the improvement.

采用迭代测试与改进。如果纸板模型显示某连接处薄弱，就加固并重新测试——然后记录失败与改进的过程。

9. Sustainability and Life Cycle Assessment | 可持续性与生命周期评估

Students sometimes think that a material labelled “natural” is automatically sustainable. Sustainability must consider the whole life cycle: raw material extraction, manufacturing, transport, use, and disposal. A bamboo product shipped across the globe may have a higher carbon footprint than locally sourced recycled plastic.

学生有时会认为标有“天然”的材料就自动是可持续的。可持续性必须考虑整个生命周期：原材料提取、制造、运输、使用和废弃处理。一个跨洋运输的竹制品，碳足迹可能比本地采购的再生塑料还要高。

The 6Rs (Reduce, Reuse, Recycle, Rethink, Refuse, Repair) provide a framework. A frequent error is thinking recycling is always the best option; in practice, reusing a product or reducing material use saves more energy. When writing about design for the environment, mention:

6R原则（减少、重复使用、回收、重新思考、拒绝、修复）提供了一个框架。一个常见错误是认为回收永远是最佳选择；实际上，重复使用产品或减少材料用量能节约更多能源。在撰写环保设计内容时，要提到：

Design for disassembly – so components can be separated for recycling.

面向拆解的设计——使零部件可分离以便回收。
Energy recovery through incineration with heat capture is a valid end-of-life option if materials cannot be recycled.

如果材料无法回收，通过带热回收的焚烧进行能量回收是有效的寿命终止选项。
Avoid greenwash: be specific about measurable impact, e.g. ‘30% reduction in packaging mass’.

避免“漂绿”：要具体说明可衡量的影响，如“包装质量减少30%”。

10. Units and Significant Figures | 单位与有效数字

Incorrect unit conversion is one of the most penalised mistakes. For engineering calculations, all quantities must be in SI base units unless otherwise specified. A student might use cm for area while force is in newtons, leading to nonsense results. Always convert: 1 cm = 0.01 m, 1 mm = 0.001 m, 1 kPa = 1000 Pa.

单位换算错误是扣分最多的错误之一。进行工程计算时，所有量都必须使用国际单位制基本单位，除非另有说明。学生可能用厘米表示面积，而力用牛顿，导致荒谬的结果。始终要换算：1 cm = 0.01 m，1 mm = 0.001 m，1 kPa = 1000 Pa。

Significant figures matter. If a measured length is given as 2.50 m, it has three significant figures; a calculated stress should not be quoted as 125.6789 Pa. Match the precision of the least accurate input. Also, remember that zeroes before the first non-zero digit are not significant: 0.0045 has two significant figures (4 and 5).

有效数字很重要。如果给出的测量长度是2.50 m，它有三位有效数字；计算出的应力不应写成125.6789 Pa。要匹配最不精确输入数据的精度。还要记住，第一个非零数字前的零不是有效数字：0.0045有两位有效数字（4和5）。

When plotting graphs, label axes with quantity, unit, and sensible scales. Do not forget to write the units in brackets, e.g. Force (N). If you calculate a gradient, state its units clearly.

绘图时，坐标轴要标出量、单位和合理刻度。不要忘记将单位写在括号里，例如 Force (N)。如果计算斜率，要清楚标明其单位。

11. Levers and Mechanical Advantage | 杠杆与机械利益

Students often misidentify the fulcrum, load, and effort in a lever system. Mechanical advantage (MA) is calculated as load ÷ effort. A MA greater than 1 means the lever multiplies the effort force. However, in a third-class lever (e.g. tweezers), MA is less than 1 because the effort is between the fulcrum and load — you gain speed and distance at the expense of force.

学生经常错误辨认杠杆系统中的支点、负载和作用力。机械利益（MA）等于负载除以作用力。MA大于1表示该杠杆放大了作用力。然而，在第三类杠杆（如镊子）中，MA小于1，因为作用力在支点和负载之间——你牺牲力来换取速度和距离。

A common mistake is thinking that a lever can increase energy. Energy is conserved; levers trade force for distance. If you lift a 600 N load 0.2 m using an effort that moves 1.2 m, the ideal effort is 100 N (ignoring friction). The ratio of distances equals the velocity ratio (VR).

一个常见错误是认为杠杆可以增加能量。能量是守恒的；杠杆用距离换取力。如果你用作用力移动1.2 m举起600 N的负载0.2 m，理想作用力为100 N（忽略摩擦）。距离之比等于速比（VR）。

MA = Load / Effort, VR = distance moved by effort / distance moved by load

Efficiency = (MA / VR) × 100%. Real machines have friction, so MA is always less than VR. When solving problems, draw a labelled diagram first.

效率 = (MA / VR) × 100%。真实机械存在摩擦，因此MA总是小于VR。解题时，请先画出标注示意图。

12. Systems Thinking: Input-Process-Output | 系统思维：输入-处理-输出

Year 10 engineering often requires students to view devices as systems. A common mistake is to describe only the physical components and ignore the energy flow or signal processing. Every system can be broken into input, process, and output blocks. For a temperature alarm: input is a thermistor (sensor), process is a comparator circuit, output is a buzzer or LED.

10年级工程学常常要求学生将装置视为系统。一个常见错误是只描述物理元件，而忽略能量流动或信号处理。每个系统都可分解为输入、处理和输出模块。对于温度报警器：输入是热敏电阻（传感器），处理是比较器电路，输出是蜂鸣器或LED。

Students also fail to differentiate between open-loop and closed-loop control. A kettle with a bimetallic strip that switches off at a set temperature is closed-loop because it uses feedback. A simple electric heater without a thermostat is open-loop — there is no automatic correction.

学生也常常分不清开环控制与闭环控制。带有双金属片且在设定温度下断电的水壶是闭环系统，因为它使用了反馈。没有恒温器的简单电热器是开环的——没有自动校正。

When designing circuits, consider the subsystem blocks and how they interact. A microcontroller can be the process block, taking sensor signals and activating motors. Always ensure signal levels are compatible (e.g. 0–5 V digital output to a relay module).

设计电路时，要考虑子系统模块以及它们如何互动。微控制器可作为处理模块，接收传感器信号并驱动电机。始终确保信号电平兼容（例如0–5 V数字输出到继电器模块）。

Published by TutorHao | Engineering Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Year 10 WJEC Engineering: Common Misconceptions and Correction Methods | WJEC 10年级工程：常见误区与纠正方法