📚 Case Study Practical Exercises: Investigating Paper Towel Absorbency | 案例分析实战演练：调查纸巾吸水性
In Year 7 OCR Science, case study practical exercises help you apply scientific skills to real-world problems. This article walks you through a full investigation into paper towel absorbency, from forming a question to evaluating the method. By the end, you will understand how to plan an experiment, identify variables, record results, and draw a trustworthy conclusion—just like a scientist does in the lab.
在七年级 OCR 科学中，案例分析实战演练帮助你运用科学技能解决现实问题。本文将带你完成一项关于纸巾吸水性的完整探究，从提出问题到评估方法。读完后，你将理解如何设计实验、识别变量、记录结果并得出可靠的结论——就像科学家在实验室里所做的那样。
1. Introduction to the Case Study | 案例研究简介
Paper towels are everyday items, but their ability to soak up liquid varies greatly between brands. Understanding absorbency means exploring how a material’s structure and composition affect its function. In this case study, we compare three different brands of paper towels to find out which one absorbs the most water. This investigation will guide you through every step of a scientific inquiry, building skills that you can apply to many other experiments.
纸巾是日常用品，但不同品牌的吸水能力差异很大。理解吸水性意味着探索材料的结构和成分如何影响其功能。在这个案例研究中，我们比较三种不同品牌的纸巾，找出哪一种吸水最多。这项探究将引导你经历科学探究的每一个步骤，培养你可以应用到许多其他实验中的技能。
2. The Scientific Question | 科学问题
A testable scientific question is specific and focuses on a measurable outcome. For this investigation, the question is: ‘Which brand of paper towel absorbs the greatest mass of water per sheet?’ By asking this, we make sure we can collect numerical data and avoid vague comparisons. The question also prompts us to consider how we will measure absorption and what ‘greatest mass’ actually means in a fair test.
一个可测试的科学问题应当是具体的，并聚焦于可测量的结果。在这项探究中，问题是：“每张纸巾哪种品牌吸收的水质量最大？” 提出这个问题可以确保我们能够收集数值数据，避免模糊的比较。这个问题还促使我们思考如何测量吸水量，以及在公平测试中“最大质量”究竟意味着什么。
3. Forming a Hypothesis | 提出假设
Before you start an experiment, you should make a prediction based on prior knowledge or observations. A hypothesis is a statement that can be tested. For example, you might write: ‘If I change the brand of paper towel, then the mass of water absorbed will be different, because some brands have thicker fibres or more air spaces between fibres.’ Write your hypothesis clearly so that you can refer back to it when drawing your conclusion.
开始实验之前，你应该根据先验知识或观察做出预测。假设是一个可以被验证的陈述。例如，你可以写：“如果我改变纸巾品牌，那么吸收的水的质量会不同，因为某些品牌纤维更厚或者纤维之间有更多空气间隙。” 清晰地写下你的假设，这样你在得出结论时可以回顾它。
4. Identifying Variables | 确定变量
The independent variable is what you change on purpose—here, it is the brand of paper towel. You test at least three different brands to see the effect.
自变量是你有意改变的因素——在这里是纸巾的品牌。你至少测试三个不同的品牌来观察效果。
The dependent variable is what you measure—the mass of water absorbed by each sheet. You can measure this by weighing the paper towel before and after dipping it in water.
因变量是你测量的量——每张纸巾吸收的水的质量。你可以通过在浸水前后称量纸巾来测量这个量。
Control variables are the factors you keep the same to ensure a fair test. These include the size of each towel (cut to the same area), the volume of water used, the time the towel is submerged, the temperature of the water, and how you drain excess water.
控制变量是你保持不变的因素，以确保测试公平。这些包括每张纸巾的尺寸（剪成相同面积）、所用的水量、纸巾浸没的时间、水温以及沥去多余水分的方式。
5. Planning the Method | 设计实验方法
Write a step-by-step method that anyone could follow. Start by gathering equipment: three brands of paper towel, scissors, a ruler, a 250 cm³ beaker, 200 cm³ of room-temperature water, a balance (scale) reading to 0.1 g, a stopwatch, and a tray. Then outline the procedure:
Step 1: Cut each paper towel into identical squares of 10 cm x 10 cm.
Step 2: Use the balance to measure the mass of one dry square and record it.
Step 3: Pour exactly 200 cm³ of water into the beaker.
Step 4: Submerge the square fully in the water and start the stopwatch. Leave it for 30 seconds.
Step 5: Carefully lift the square out with tongs, let it drip for 5 seconds over the beaker, then place it on the balance. Measure the mass of the wet towel immediately.
Step 6: Repeat steps 2–5 for two more squares of the same brand, then switch to the next brand.
写一个任何人都能遵循的逐步方法。首先收集设备：三个品牌的纸巾、剪刀、尺子、一个 250 cm³ 的烧杯、200 cm³ 室温水、一台读数精确到 0.1 g 的天平、一个秒表和一个托盘。然后概述步骤：
第1步：将每张纸巾剪成 10 cm × 10 cm 的相同方形。
第2步：用天平测量一片干燥方形的质量并记录。
第3步：准确量取 200 cm³ 水倒入烧杯。
第4步：将方形完全浸入水中并启动秒表。保留 30 秒。
第5步：用镊子小心取出方形，在烧杯上方滴沥 5 秒，然后放在天平上。立即测量湿纸巾的质量。
第6步：对同一品牌的另外两片方形重复步骤2–5，然后换到下一个品牌。
6. Carrying Out the Experiment | 进行实验
When you perform the experiment, follow the method precisely. Use the same water source and temperature for all trials. It is a good idea to label each square so you do not mix up brands. Record your observations, such as any towel that tears or struggles to hold water. Safety note: mop up any spills straight away and wash hands after handling wet materials. Collecting data carefully now will make your conclusion more reliable later.
进行实验时，要精确遵循方法。所有试验使用相同的水源和水温。最好给每个方形贴标签以免混淆品牌。记录你的观察，例如是否有纸巾撕裂或难以吸水。安全提示：立即擦干泼溅出的水，处理湿材料后洗手。现在仔细收集数据，会使后面的结论更可靠。
7. Recording Results | 记录结果
Record your measurements in a clear results table. For each trial, you calculate the mass of water absorbed by subtracting the dry mass from the wet mass. Here is an example table with hypothetical data:
将你的测量数据清晰地记录在结果表格中。每个试验中，用湿质量减去干质量计算吸收的水质量。下面是一个带有假设数据的示例表格：
| Brand | Trial | Dry mass (g) | Wet mass (g) | Mass of water absorbed (g) |
|---|---|---|---|---|
| A | 1 | 1.2 | 9.8 | 8.6 |
| A | 2 | 1.3 | 10.1 | 8.8 |
| A | 3 | 1.2 | 9.6 | 8.4 |
| B | 1 | 1.5 | 11.7 | 10.2 |
| B | 2 | 1.4 | 11.5 | 10.1 |
| B | 3 | 1.5 | 11.9 | 10.4 |
| C | 1 | 1.7 | 14.5 | 12.8 |
| C | 2 | 1.6 | 14.0 | 12.4 |
| C | 3 | 1.7 | 14.2 | 12.5 |
Always include units and repeat each trial three times. Repeats allow you to spot anomalies and calculate a mean value. In a real investigation, you would record your own data here.
务必包含单位，每个试验重复三次。重复可以让你发现异常值并计算平均值。在实际探究中，你将在这里记录你自己的数据。
8. Analysing Data | 数据分析
After recording your results, calculate the mean mass of water absorbed for each brand. Use only the results that seem consistent; if one trial looks very different, you might identify it as an anomaly and exclude it from the mean. For Brand C, the mean is:
记录结果后，计算每种品牌吸收水的平均质量。只使用看起来一致的结果；如果某个试验数据看起来差异很大，你可以将其视为异常值并排除在平均值计算之外。对于品牌C，平均值为：
Mean mass absorbed (C) = (12.8 g + 12.4 g + 12.5 g) ÷ 3 = 12.6 g
Compare the mean values. In our example, Brand A averaged 8.6 g, Brand B 10.2 g, and Brand C 12.6 g. You can display these values on a bar chart, with brand on the x-axis and mean mass absorbed on the y-axis. A bar chart makes it easy to spot patterns and communicate your findings.
比较平均值。在我们的示例中，品牌A平均为 8.6 g，品牌B为 10.2 g，品牌C为 12.6 g。你可以将这些数值展示在条形图上，x轴为品牌，y轴为吸收水质量的平均值。条形图便于发现规律并传达你的发现。
9. Drawing a Conclusion | 得出结论
Your conclusion should refer back to the original question and your hypothesis. State clearly which brand absorbed the most water and support this with data. For example: ‘Brand C absorbed the greatest mass of water, with a mean of 12.6 g per sheet. This supports my hypothesis that brands with thicker fibres absorb more water. Brand A absorbed the least, averaging 8.6 g.’ Do not forget to explain why you think the results turned out that way, linking to fibre structure or air gaps.
你的结论应回溯最初的问题和假设。清楚地说明哪个品牌吸水最多，并用数据支持。例如：“品牌C吸收的水质量最大，平均每张 12.6 g。这支持了我的假设，即纤维更厚的品牌吸收更多的水。品牌A吸收最少，平均为 8.6 g。” 别忘记解释你认为结果为何如此，可与纤维结构或空气间隙相联系。
10. Evaluating the Investigation | 评估实验
A strong evaluation identifies how trustworthy the results are and suggests improvements. Consider these points: Was the method fair? Did you control all variables—size, water volume, submersion time, and dripping time? Could some water have dripped away before weighing? Did you zero the balance correctly? Also, discuss repeatability: if you repeated the whole investigation on another day, would you get similar results? To improve, you could use a measuring cylinder to catch drips, or use more brands and a larger number of repeats to increase reliability.
一个有力的评估会指出结果的可靠程度并提出改进建议。考虑以下几点：方法是否公平？你是否控制了所有变量——尺寸、水量、浸没时间和滴沥时间？在称量之前是否可能有一些水滴落？天平调零是否正确？同时，讨论可重复性：如果你在另一天重复整个探究，会得到类似的结果吗？为了改进，你可以使用量筒接住滴落的水，或使用更多品牌和更多次重复以增强可靠性。
11. Applying to Other Contexts | 应用到其他情境
Once you have mastered this case study, you can adapt the same structure to investigate other questions. For example, you could test how the temperature of water affects the speed at which a sugar cube dissolves, or how the type of surface affects the distance a toy car rolls. The skills of identifying variables, writing a method, collecting data, and evaluating stay the same. Always ask yourself: ‘Is my test fair? Have I collected enough evidence?’. Using case studies like this builds your confidence to think and work scientifically.
一旦掌握了这个案例研究，你便可以将同样的结构应用来探究其他问题。例如，你可以测试水温如何影响方糖溶解的速度，或者表面类型如何影响玩具车行驶的距离。识别变量、撰写方法、收集数据和评估这些技能保持不变。始终问自己：“我的测试公平吗？我收集了足够的证据吗？” 运用这样的案例研究能帮助你树立信心，像科学家一样思考和工作。
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