📚 Catapult Design Challenge: A Case Study in Engineering | 弹射器设计挑战：工程案例分析实战
In this case study, we will go through a complete engineering design challenge: building a small catapult to launch a marshmallow or soft projectile. You will follow the steps real engineers use—defining the problem, researching, designing, building, testing, and improving. This hands-on project is a great way to understand forces, materials, and the engineering design process in a fun and practical way.
在这份案例分析中，我们将完成一个完整的工程设计挑战：制作一个小型弹射器，用来发射棉花糖或软性投射物。你将按照真实工程师的步骤——定义问题、研究、设计、建造、测试和改进——来进行。这个动手项目是理解力、材料和工程设计过程的一种有趣而实用的方式。
1. Introduction to the Case Study | 案例介绍
Engineering is all about solving problems and creating useful devices. In this case study, you are challenged to design and build a desktop catapult that can launch a small marshmallow a distance of at least 3 metres and hit a paper cup target. You will work with everyday materials such as lolly sticks, rubber bands, and a plastic spoon. The goal is not just to make something that works, but to understand why it works and how you could make it better.
工程学就是解决问题和创造有用的装置。在这个案例分析中，你需要设计并建造一个桌面弹射器，能够将一个小棉花糖发射至至少 3 米远并击中一个纸杯目标。你将使用日常材料，如冰棒棍、橡皮筋和一个塑料勺。目标不仅仅是做出一个能用的东西，而是要理解它为什么能工作，以及如何让它变得更好。
2. Understanding the Design Brief | 理解设计任务书
Every engineering project starts with a design brief. Your brief states: “Design a lightweight catapult that can launch a standard marshmallow (about 5 g) horizontally or at an angle. It must be stable on a desk, easy to operate, and made only from wood sticks, rubber bands, tape, and a spoon. The catapult should achieve a range of 3 m or more and show reasonable accuracy when aimed at a target.” This brief sets clear constraints on materials, performance, and safety.
每个工程项目都从一份设计任务书开始。你的任务书写道：“设计一个轻型弹射器，能水平或以一定角度发射一枚标准棉花糖（约 5 克）。它必须在桌面上稳定、易于操作，并且只使用木棒、橡皮筋、胶带和一把勺子制作。弹射器应达到 3 米或更远的射程，并在瞄准目标时表现出合理的准确性。”这份任务书在材料、性能和安全方面设定了明确的限制。
3. Researching Forces and Motion | 研究力与运动
ectile. The key concepts are: elastic potential energy (E = ½ kx², where k is the spring constant and x is the stretch distance), levers (class 1 or class 3), and projectile motion. The ideal launch angle for maximum range on flat ground is 45°, but you can test different angles. Also, consider air resistance and friction in the pivot point.
在建造之前，你需要理解背后的科学原理。弹射器将能量储存在拉伸的橡皮筋中，然后将能量传递给投射物。关键概念包括：弹性势能（E = ½ kx²，其中 k 是弹性系数，x 是拉伸距离）、杠杆（一类或三类杠杆）以及抛体运动。在平地上获得最大射程的理想发射角是 45°，但你可以测试不同角度。此外，还要考虑空气阻力以及支点处的摩擦力。
4. Sketching and Brainstorming | 草图与头脑风暴
Good engineers always sketch their ideas before building. Draw at least two different catapult designs. Label the key parts: the base, the throwing arm, the fulcrum (pivot point), the elastic band attachment, and the projectile cup. Think about whether you want a fixed or adjustable launch angle. Use a simple table to compare the pros and cons of each design idea.
优秀的工程师在建造之前都会画草图。至少绘制两种不同的弹射器设计方案。标注关键部件：底座、投掷臂、支点（旋转点）、橡皮筋固定点和弹射杯。考虑想要固定的还是可调节的发射角度。用一个简单的表格来比较每种设计方案的优缺点。
5. Material Selection | 材料选择
Although materials are limited by the brief, you still have choices. Lolly sticks can be wide or narrow, rubber bands vary in thickness and length, and spoons can be plastic or wooden. When selecting materials, think about stiffness, elasticity, weight, and ease of joining. For example, thicker rubber bands store more energy but require more force to stretch. A lighter throwing arm means more of the stored energy goes into the projectile, not the arm itself.
尽管材料受任务书限制，但你仍然有选择余地。冰棒棍可宽可窄，橡皮筋的粗细和长度各不相同，勺子可以是塑料或木质的。选择材料时，要考虑刚度、弹性、重量和连接难易程度。例如，较粗的橡皮筋储存更多能量，但需要更大的力来拉伸。更轻的投掷臂意味着更多的储存能量传递给投射物，而不是消耗在臂本身上。
6. Building the Prototype: Step-by-Step | 构建原型：步骤详解
Start by assembling the base. Stack and tape four lolly sticks together to form a sturdy foundation. Then create the throwing arm by taping a plastic spoon to the end of a single lolly stick. Position the fulcrum by wrapping a rubber band around a stack of sticks near the centre of the arm. Attach the elastic band that powers the launch—one end to the front of the base, the other to the throwing arm near the fulcrum. Make sure all joints are secure and that the arm can pivot freely without too much wobble.
首先组装底座。将四根冰棒棍叠起来并粘贴牢固，形成一个稳固的基础。然后制作投掷臂，将一个塑料勺贴在一根单独的冰棒棍末端。用橡皮筋在投掷臂中部附近缠绕一叠木棒作为支点。固定提供发射动力的橡皮筋——一端连在底座前方，另一端连在投掷臂靠近支点的位置。确保所有连接牢固，投掷臂能自由转动而不会过度晃动。
7. Testing and Data Collection | 测试与数据收集
Testing is where you gather evidence. Set up a measuring tape on the floor and launch the marshmallow at a consistent angle (use a protractor to measure). Record the distance travelled for five trials, then change one variable, such as the number of rubber bands or the launch angle. Create a simple data table like the one below to compare results.
| Trial | Angle (°) | No. of Rubber Bands | Distance (cm) |
|---|---|---|---|
| 1 | 45 | 1 | 280 |
| 2 | 45 | 1 | 272 |
| 3 | 30 | 2 | 315 |
Testing is where you gather evidence. Set up a measuring tape on the floor and launch the marshmallow at a consistent angle (use a protractor to measure). Record the distance travelled for five trials, then change one variable, such as the number of rubber bands or the launch angle. Create a simple data table like the one above to compare results. Look for patterns: did more elastic energy increase range? Did a lower angle give a flatter, longer flight?
测试是收集证据的环节。在地板上放置卷尺，以一致的角度（用量角器测量）发射棉花糖。记录五次试验的飞行距离，然后改变一个变量，比如橡皮筋的数量或发射角度。制作一个像上面那样的简单数据表来比较结果。寻找规律：更多的弹性能量是否增加了射程？更低的角度是否带来了更平直、更远的飞行？
8. Iterating the Design | 设计迭代
Engineering is rarely right the first time. Based on your test data, think about what could be improved. Perhaps the base wobbles when you release the arm, wasting energy. You might add side supports or weight to the base. If the marshmallow slips off the spoon too early, you can adjust the cup shape with tape or change the release angle. Make one change at a time and re‑test so you can clearly see the effect of each modification. Document every iteration in a design log.
工程极少能一次成功。根据你的测试数据，想一想哪些地方可以改进。也许释放投掷臂时底座会晃动，浪费了能量。你可以增加侧向支撑或在底座上加重。如果棉花糖提早从勺中滑脱，你可以用胶带调整杯形或改变释放角度。每次只做一项修改并重新测试，这样你就能清晰地看到每项改进的效果。在设计日志中记录每一次迭代。
9. Presenting the Engineering Report | 展示工程报告
Communication is a vital engineering skill. Prepare a short report or presentation that includes: your initial sketches and final design drawing with labels, a summary of your tests (including the data table and a simple bar chart), an explanation of the science behind your catapult, and a reflection on what you would do differently if you had more time. Use clear, precise language and avoid vague descriptions.
沟通是一项至关重要的工程技能。准备一份简短的报告或演示，内容包括：你的初始草图和带标注的最终设计图、测试总结（包括数据表和一个简单的条形图）、弹射器背后的科学原理说明，以及对于如果拥有更多时间你会做出哪些不同改进的反思。使用清晰、精确的语言，避免模糊的描述。
10. Key Engineering Principles Recap | 关键工程原理回顾
Let us summarise the core principles you have applied. Energy transfer: elastic potential energy → kinetic energy of the arm and projectile. Levers: a catapult is a third-class lever where the effort is between the fulcrum and the load, multiplying speed. Forces: tension in the rubber band, air resistance, gravity, and normal force from the base. Projectile motion: a parabolic path determined by launch speed, angle, and height. Understanding these makes you a better engineer, not just a builder.
让我们总结一下你应用的核心原理。能量转换：弹性势能 → 投掷臂和投射物的动能。杠杆：弹射器是一个第三类杠杆，施力点在支点和负载之间，从而放大了速度。力：橡皮筋中的张力、空气阻力、重力以及来自底座的支持力。抛体运动：由发射速度、角度和高度决定的抛物线路径。理解这些使你成为更好的工程师，而不仅仅是一个建造者。
11. Conclusion: From Classroom to Real World | 结论：从课堂到现实世界
This catapult challenge is a small-scale model of how engineers tackle real problems—from designing safer cars to launching spacecraft. The engineering design process of defining, researching, ideating, prototyping, testing, and iterating is universal. By practising this process, you build critical thinking, creativity, and resilience. Keep your design log, because every failure is just another data point that leads to success.
这个弹射器挑战是工程师解决真实问题——从设计更安全的汽车到发射航天器——的一个缩小版模型。定义、研究、构思、原型制作、测试和迭代的工程设计过程是普遍适用的。通过实践这一过程，你培养了批判性思维、创造力和韧性。保存好你的设计日志，因为每一次失败都是通往成功的又一个数据点。
Published by TutorHao | Engineering Revision Series | aleveler.com
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