📚 Year 7 Edexcel Science: Case Study Practical Exercises | 七年级Edexcel科学：案例分析实战演练
In Year 7 Edexcel Science, working scientifically is a core skill, not an optional extra. You will often be given a case study in which you must plan an investigation, identify variables, collect and record data, plot a graph, and evaluate your results. This article is a complete practical walkthrough of one classic case study: investigating which material keeps a hot drink warm for the longest time. By following every step, you will strengthen your understanding of variables, fair testing, graphing, heat transfer and scientific conclusions - all of which are essential for your KS3 assessments and for the skills you will carry into GCSE.
在七年级爱德思科学中，"科学地工作"是一项核心技能，而不是可有可无的附加内容。你经常会遇到案例研究，需要规划调查、识别变量、收集并记录数据、绘制图表并评估结果。本文对一个经典案例研究进行完整的实战演练：探究哪种材料能让热饮保温最久。通过逐步推进，你将加深对变量、公平测试、图表绘制、热传递和科学结论的理解——这些内容对 KS3 测评至关重要，也会成为你带入 GCSE 阶段的核心能力。
1. Understanding the Case Study Scenario | 理解案例情景
Your teacher gives you four identical beakers, each filled with 200 cm³ of hot water at 80 °C. Each beaker is wrapped in a different material: cotton wool, aluminium foil, newspaper, and bubble wrap. Your aim is to determine which material is the best insulator - the one that reduces heat loss to the surroundings most effectively. Read the scenario twice before you touch any equipment, and underline every quantity and every material mentioned. Examiners often hide the key information in the middle of the paragraph.
老师给你四个相同的烧杯，每个装有 200 cm³、80 °C 的热水。每个烧杯分别包裹不同的材料：棉絮、铝箔、报纸和气泡膜。你的目标是确定哪种材料是最好的隔热体——它能最有效地减少向周围环境的热量散失。在接触任何器材之前，先把情景读两遍，并划出所有提到的数量和材料。命题人常常把关键信息藏在段落的中间。
- Independent variable: the material used to wrap the beaker.
自变量：用来包裹烧杯的材料。 - Dependent variable: the temperature of the water after a set time.
因变量：经过设定时间后水的温度。 - Control variables: everything else that could affect heat loss.
控制变量：其他所有可能影响热量散失的因素。
2. Identifying the Variables | 识别变量
A variable is anything that can change during an investigation. Getting the three types clear is the single most reliable way to gain marks in a practical question. The independent variable is the one you deliberately change. The dependent variable is the one you measure. Control variables are the ones you keep the same so that the test is fair.
变量是指调查过程中会发生改变的任何因素。把三类变量分清楚，是实践题中拿分最可靠的方法。自变量是你有意改变的因素；因变量是你测量的因素；控制变量是你保持不变的、以确保测试公平的因素。
| Type of variable | In this investigation | 中文说明 |
| Independent | The insulating material: cotton wool, foil, newspaper, bubble wrap | 自变量：保温材料（棉絮、铝箔、报纸、气泡膜） |
| Dependent | Water temperature (°C) measured every 2 minutes for 10 minutes | 因变量：每 2 分钟测量一次水温（°C），持续 10 分钟 |
| Control | Volume of water, starting temperature, beaker size, room temperature, wrapping thickness, thermometer used | 控制变量：水的体积、初始温度、烧杯规格、室温、包裹层厚度、所用温度计 |
Write the variables down in a three-line list before you write your method. This habit saves time later, because the same list can be reused in your table heading, your graph axes and your conclusion.
在写实验方法之前，先用三行清单把变量写下来。这个习惯能节省后面的时间，因为同一份清单可以直接用于表格标题、图表坐标轴和结论部分。
3. Writing a Testable Hypothesis | 写出可检验的假设
A hypothesis is not a guess without reason. It is a prediction supported by scientific ideas. A strong hypothesis has three parts: what you think will happen, why you think it will happen, and how you will know if you were right. Vague statements such as "cotton wool is warm" earn nothing; link your prediction to trapped air and heat transfer.
假设不是没有根据的猜测，而是有科学依据支撑的预测。一个好的假设包含三部分：你认为会发生什么、为什么认为会发生、以及你如何判断自己是否正确。像"棉絮很暖和"这样的模糊表述是拿不到分数的；要把预测与被困住的空气和热传递联系起来。
Hypothesis: Cotton wool will be the best insulator because it traps the most air, and trapped air reduces conduction and convection.
假设：棉絮将是最好的隔热体，因为它困住的空气最多，而静止空气会削弱热传导和热对流。
Notice that the hypothesis mentions a mechanism. If you simply say "cotton wool is best", the examiner cannot tell whether you understand insulation or whether you are repeating something you heard. Adding "because trapped air is a poor conductor of heat" turns a guess into a scientific prediction.
注意，这个假设提到了机制。如果你只说"棉絮最好"，阅卷老师无法判断你是真的理解保温原理，还是仅仅在重复听说过的话。加上"因为静止空气是热的不良导体"，就把猜测变成了科学预测。
4. Designing a Fair Test | 设计公平测试
A fair test means only one thing changes between the experimental runs. If the beaker wrapped in foil holds less water than the beaker wrapped in cotton wool, you cannot tell whether the difference in cooling came from the material or from the smaller volume of water. Both factors would be acting at once, so the results would be invalid.
公平测试意味着各次实验之间只有一个因素发生变化。如果包裹铝箔的烧杯装的水比包裹棉絮的烧杯少，你就无法判断降温差异是来自材料，还是来自水量不同。两个因素同时起作用，结果就是无效的。
- Use the same volume of water - 200 cm³ - in every beaker.
每个烧杯使用相同体积的水——200 cm³。 - Start every beaker at the same temperature, 80 °C, checked with the same thermometer.
每个烧杯起始温度相同，均为 80 °C，并用同一支温度计确认。 - Wrap every beaker with the same number of layers, so the thickness is comparable.
每个烧杯包裹相同层数，使厚度可比。 - Leave all four beakers in the same room, on the same bench, away from draughts and direct sunlight.
把四个烧杯放在同一房间、同一实验台上，避开气流和直射阳光。 - Either put a lid on all four or on none - never a mixture.
四个烧杯要么全部加盖，要么全部不加盖，绝不能混用。 - Measure at exactly the same time intervals using the same stopwatch.
用同一只秒表，在完全相同的时间间隔读数。
A useful sentence to include in your write-up is: "All variables except the insulating material were kept constant to ensure a fair test." Examiners look for that phrase because it shows you have thought about validity, not just about following instructions.
写作时可以用这样一句话："除保温材料外，所有变量均保持恒定，以确保测试公平。"阅卷老师会寻找这类表述，因为它说明你思考了实验的有效性，而不仅仅是在照做步骤。
5. Step-by-Step Procedure | 分步操作流程
Practical questions frequently ask you to write a method that another student could follow without asking questions. Numbered steps, precise quantities and named equipment all earn credit. Below is a model method for this case study.
实践题经常要求你写出另一位同学能照着直接做的实验方法。编号步骤、精确用量和明确器材都能得分。下面是本案例研究的示范方法。
- Measure 200 cm³ of hot water at 80 °C into each of four identical beakers.
向四个相同烧杯中各量取 200 cm³、温度为 80 °C 的热水。 - Wrap one beaker in cotton wool, one in aluminium foil, one in newspaper, one in bubble wrap, using the same number of layers each time.
分别用一个烧杯包棉絮、一个包铝箔、一个包报纸、一个包气泡膜，每次使用相同层数。 - Place a thermometer in the water of the first beaker, wait 30 seconds for it to reach the water temperature, and record the starting temperature.
把温度计放入第一个烧杯的水中，等 30 秒使其达到水温，记录起始温度。 - Start the stopwatch and record the temperature every 2 minutes for 10 minutes.
启动秒表，每 2 分钟记录一次温度，共 10 分钟。 - Repeat steps 1 to 4 for the other three materials.
对其余三种材料重复步骤 1 至 4。 - Repeat the whole investigation a second time to check for reliability.
把整个调查再重复一次，以检查可靠性。
Do not stir only one beaker, and do not take the thermometer out while reading it. Small inconsistencies like these are exactly what evaluation questions are designed to expose.
不要只搅拌其中一个烧杯，也不要把温度计拿出来读数。正是这类细节上的不一致，会成为评估类问题的考点。
6. The Science Behind Insulation | 保温背后的科学原理
Heat always moves from a hotter place to a cooler place. There are three ways it does so: conduction, convection and radiation. A good insulator slows down one or more of these processes. Cotton wool and bubble wrap work mainly by trapping air, because still air is a very poor conductor of heat.
热量总是从较热的地方传向较冷的地方，传递方式有三种：传导、对流和辐射。好的隔热体会减慢其中一种或多种过程。棉絮和气泡膜主要依靠困住空气来起作用，因为静止空气是热的不良导体。
- Conduction: particles pass energy along by vibrating and colliding. Metals conduct well because they have free electrons.
传导：粒子通过振动和碰撞传递能量。金属导热好，因为它们有自由电子。 - Convection: warmer, less dense fluid rises and cooler fluid sinks, forming a circulation current.
对流：较热、密度较小的流体上升，较冷的流体下沉，形成循环流动。 - Radiation: energy travels as infrared waves and needs no particles. Shiny surfaces reflect it; dull black surfaces absorb and emit it well.
辐射：能量以红外波形式传播，不需要粒子。光亮表面会反射它，暗黑色表面则善于吸收和发射。
This explains a subtle result. Aluminium foil is a metal and therefore an excellent conductor, so it should be a poor insulator. However, its shiny surface reflects infrared radiation back towards the beaker. In this investigation the extra conduction usually outweighs the reflection, so foil performs worst - but a strong answer will mention both effects rather than only one.
这就解释了一个微妙的结果。铝箔是金属，因此是极好的导体，理论上应该是很差的隔热体。但它光亮的表面会把红外辐射反射回烧杯。在本调查中，额外的传导通常超过反射带来的好处，所以铝箔表现最差——但优秀的答案会同时提到这两种效应，而不是只提一种。
7. Risk Assessment and Safety | 风险评估与安全
Every practical write-up should include a short risk assessment. A hazard is something that could cause harm; the risk is the chance of that harm actually happening; a control measure reduces the risk. Hot water at 80 °C is the main hazard here, and it must be handled with care.
每份实验报告都应包含简短的风险评估。危险源是可能造成伤害的事物；风险是该伤害真正发生的可能性；控制措施则用来降低风险。80 °C 的热水是这里的主要危险源，必须小心处理。
| Hazard 危险源 | Risk 风险 | Control 控制措施 |
| Hot water at 80 °C | Scalds to skin if spilled | Use a heatproof mat, pour slowly, keep beakers away from the bench edge |
| Glass beakers | Breakage causing cuts | Carry with both hands, report cracks immediately |
| Water near electrical sockets | Electric shock | Keep water away from plugs and leads, wipe spills at once |
Safety points should be specific. "Be careful" is not a control measure; "pour the water over the sink and wear safety glasses" is. Always tie back long hair and clear bags from the floor before starting.
安全要点必须具体。"小心一点"不是控制措施；"在水槽上方倒水并佩戴护目镜"才是。开始实验前务必把长发扎起，并把地上的书包清走。
8. Collecting and Recording Data | 数据收集与记录
rst column and the dependent variable in the others. Always note the precision of your thermometer - most school thermometers read to ±0.5 °C, so writing 67.37 °C would be a false claim of accuracy.
数据必须记录在标题清晰、单位正确、小数位一致的表格中。自变量通常放在第一列，因变量放在其余列。一定要记录温度计的精度——多数学校温度计读数精度为 ±0.5 °C，因此写 67.37 °C 是在虚报准确性。
| Time / min | Cotton wool / °C | Bubble wrap / °C | Newspaper / °C | Aluminium foil / °C |
| 0 | 80 | 80 | 80 | 80 |
| 2 | 77 | 76 | 74 | 71 |
| 4 | 74 | 73 | 69 | 64 |
| 6 | 71 | 70 | 65 | 58 |
| 8 | 69 | 68 | 62 | 55 |
| 10 | 68 | 66 | 60 | 52 |
If one reading clearly does not fit the pattern - for example, a sudden jump in temperature that the other readings do not support - record it honestly, then repeat that reading and label the original as an anomaly rather than deleting it silently. Scientific honesty is part of the mark scheme.
如果某个读数明显不符合规律——例如某一温度突然跳变，而其他读数并不支持——要如实记录，然后重测该点，并把原数据标注为异常值，而不是悄悄删掉。科学诚信本身就是评分标准的一部分。
9. Drawing Tables and Graphs | 绘制表格与图表
Temperature changes continuously with time, so a line graph is the correct choice here, not a bar chart. Put the independent variable (time) on the horizontal x-axis and the dependent variable (temperature) on the vertical y-axis. Label both axes with the quantity and its unit, and choose a scale that uses at least half of the graph paper.
温度随时间连续变化，所以这里应选择折线图，而不是柱状图。把自变量（时间）放在水平的 x 轴，把因变量（温度）放在竖直的 y 轴。两个坐标轴都要标注物理量及其单位，并选择能用满至少一半坐标纸的刻度。
- x-axis: Time / min, going from 0 to 10 in steps of 2.
x 轴：时间 / min，从 0 到 10，步长 2。 - y-axis: Temperature / °C, starting at 40 °C rather than 0 °C so that the curves are well separated.
y 轴：温度 / °C，从 40 °C 起而不是从 0 °C 起，使各条曲线彼此分开。 - Plot each material as a separate line and include a key.
每种材料画一条独立的线，并附上图例。 - Draw smooth curves or lines of best fit; do not join the dots with sharp zigzags unless the data are genuinely irregular.
画出平滑曲线或最佳拟合线；除非数据确实不规则，否则不要用尖锐的折线把点连起来。
A common error is starting the y-axis at zero, which squashes all four curves into the top of the page and makes comparison impossible. Starting at 40 °C is legitimate and shows good graphing judgement - as long as you label the axis clearly and do not break the scale mid-axis without a marker.
常见错误是把 y 轴从零开始，这会把四条曲线都压到页面顶部，使比较无法进行。从 40 °C 开始是合理的，也体现出良好的作图判断力——前提是你清楚标注了坐标轴，且在没有断轴标记的情况下不在轴中途改变刻度。
10. Analysing Results and Drawing Conclusions | 分析结果与得出结论
The steepness of each curve tells you the rate of cooling. A steeper line means faster heat loss. You can quantify this using the temperature drop divided by the time taken, which gives an average rate of cooling in °C per minute.
每条曲线的陡峭程度反映降温速率。曲线越陡，说明热量散失越快。可以用温度下降量除以所用时间进行量化，得到以 °C 每分钟表示的平均降温速率。
Rate of cooling = (T₀ − T₁) ÷ t
降温速率 = (T₀ − T₁) ÷ t
Using the sample data, cotton wool cooled from 80 °C to 68 °C in 10 minutes, a drop of 12 °C, giving a rate of 1.2 °C per minute. Aluminium foil dropped 28 °C in the same time, a rate of 2.8 °C per minute. The comparison is therefore clear and numerical rather than vague.
以示例数据为例，棉絮在 10 分钟内从 80 °C 降到 68 °C，下降了 12 °C，降温速率为每分钟 1.2 °C。铝箔在相同时间内下降了 28 °C，速率为每分钟 2.8 °C。这样比较就清晰、可量化，而不是含糊其辞。
A complete conclusion does three things: it states the pattern, it quotes evidence, and it explains the science. A model answer would read: "Cotton wool is the best insulator because the water inside it cooled slowest, falling only 12 °C in 10 minutes compared with 28 °C for foil. This is because cotton wool traps air, and trapped air is a poor conductor of heat, so less energy is transferred to the surroundings by conduction and convection."
完整的结论包含三点：说明规律、引用证据、解释科学原理。示范答案可以这样写："棉絮是最好的隔热体，因为其中的水降温最慢，10 分钟只下降 12 °C，而铝箔为 28 °C。这是因为棉絮困住了空气，而静止空气是热的不良导体，因此通过传导和对流传递给周围环境的能量更少。"
11. Evaluating the Investigation | 评估实验
Evaluation is where you judge how trustworthy your results are and suggest realistic improvements. Do not simply write "the experiment went well". Identify a specific weakness, explain its effect on the results, and propose a change that would fix it.
评估环节要判断结果在多大程度上可信，并提出切实可行的改进建议。不要只写"实验进行得很顺利"。要指出具体的不足，解释它对结果的影响，并提出能够修正它的改进方案。
| Weakness 不足 | Effect 影响 | Improvement 改进 |
| Heat lost through the open top of the beaker | All beakers cool faster, reducing the differences between materials | Put an identical lid on every beaker |
| Thermometer reads only to ±0.5 °C | Small differences may be hidden by reading error | Use a digital thermometer with 0.1 °C precision |
| Only one trial per material | An anomaly cannot be detected | Repeat each test three times and calculate a mean |
| Draughts from a nearby door | Uneven heat loss between beakers | Move the apparatus to a still corner or use a screen |
Extra credit comes from noticing that the rate of cooling is not constant. The curves flatten out as the water approaches room temperature, because the temperature difference between the water and its surroundings becomes smaller, so energy is transferred more slowly. Mentioning this shows a deeper grasp of the physics than simply reading off numbers.
加分点在于注意到降温速率并不是恒定的。随着水温接近室温，曲线会变得平缓，因为水与周围环境的温差变小，能量传递变慢。提到这一点，说明你对物理原理的把握比单纯读数更深一层。
12. Exam Technique and Common Mistakes | 考试技巧与常见错误
Case study questions reward precision. Read the command word carefully: "describe" wants what you observe, "explain" wants a scientific reason, "evaluate" wants a judgement supported by evidence. Answering an "explain" question with a description will not gain full marks, however detailed it is.
案例研究类题目奖励的是精确。要仔细看指令词："describe（描述）"要求写出你观察到的现象，"explain（解释）"要求给出科学原因，"evaluate（评估）"要求基于证据作出判断。用描述去回答"解释"类问题，无论写得多详细都拿不到满分。
- Always write units. A temperature of "68" without °C loses a mark.
永远写单位。只写"68"而不写 °C 会丢分。 - Use scientific vocabulary: insulator, conductor, conduction, convection, radiation, fair test,
广告 / Sponsored新版南艺乐理考级南京艺术学院音乐考级类基本乐理与听音训练教材乐理考级知识练习教程社会艺术水平考级教材艺术设计、音乐 备考教辅 · 正版现货 · 学习备考通用查看详情 / View on Taobao广告 / Sponsored现货速发！】新版全国中学生物理联赛决赛试题分类精编 中科大高中物理国际奥赛教材物理联赛2025高考物理自主招生培优强基…物理、生物 备考教辅 · 正版现货 · 学习备考通用查看详情 / View on Taobao
更多咨询请联系16621398022（同微信）
备考资讯每日更新，关注不错过考纲变化 · 科目分析 · 学习方法
在微信里长按二维码识别关注
或截图后用「扫一扫 → 相册」选择本图公众号：tutorhao