📚 Year 7 WJEC Physics: Case Study Practice | 七年级WJEC物理：案例分析实战演练
Case studies are a fantastic way to learn physics because they show how scientific principles apply to real-world situations. In Year 7 WJEC Physics, you will encounter scenarios that require you to apply your knowledge of forces, energy, electricity, waves, and matter. This revision guide walks you through ten practical case studies, each designed to sharpen your analytical skills and deepen your understanding. By working through these examples, you will learn how to break down problems, identify relevant concepts, and reach logical conclusions – just like a real physicist!
案例是学习物理的绝佳方式，因为它展示了科学原理如何应用于真实情境。在七年级WJEC物理课程中，你会遇到各种场景，需要运用关于力、能量、电、波和物质的知识。这本复习指南带你演练十个实用的案例，每个案例都旨在磨练你的分析能力并加深理解。通过练习这些例题，你将学会如何分解问题、识别相关概念并得出合乎逻辑的结论——就像真正的物理学家那样！
1. Case Study 1: Roller Coaster Energy | 案例一：过山车的能量
At the start of a roller coaster ride, the car is winched to the very top of a high hill. This process stores a large amount of gravitational potential energy in the car because of its height above the ground. The higher the hill, the more energy is stored.
过山车启动时，车厢会被牵引到最高坡的顶端。这个过程使得车厢储存了大量的重力势能，因为它的位置远高于地面。离地越高，储存的能量越多。
As the car rushes down the slope, the gravitational potential energy is steadily converted into kinetic energy. The car's speed increases, and at the bottom of the dip it is moving fastest – almost all the initial potential energy has been transformed into energy of motion.
当车厢冲下斜坡时，重力势能持续转化为动能。车速不断增加，在谷底时运动速度最快——几乎所有的初始势能都已转变为运动的能量。
When the car climbs the next hill, kinetic energy is transferred back into potential energy, causing it to slow down. However, some energy is always lost to the surroundings as heat and sound due to friction and air resistance. This is why each successive hill on the track must be slightly lower than the previous one; the car no longer has enough total energy to reach the same height.
当车厢爬上下一个坡时，动能又转化回势能，导致车辆减速。然而，由于摩擦和空气阻力，总有一部分能量以热和声的形式散失到周围。这就是为什么过山车轨道上每一个后续的坡都设计得比前一个略低；车厢已没有足够的能量爬升至相同高度。
Analysing the roller coaster helps you understand the principle of conservation of energy: energy cannot be created or destroyed, only transferred from one store to another. Frictional losses explain why perpetual motion is impossible.
分析过山车可以帮助你理解能量守恒原理：能量不会凭空产生或消失，只能从一个储存库转移到另一个。摩擦损失解释了为何永动机不可能实现。
2. Case Study 2: Diagnosing a Circuit Fault | 案例二：诊断电路故障
A student builds a simple series circuit containing a battery, a switch, and two identical bulbs. When the switch is closed, one bulb lights up brightly, but the other bulb remains completely dark. The student is confused because all wires appear to be connected correctly.
一位学生搭建了一个包含电池、开关和两个相同灯泡的串联电路。闭合开关后，一个灯泡亮得耀眼，另一个却完全不亮。学生很困惑，因为所有导线似乎都连接正确。
In a series circuit, the same current flows through every component. If a bulb's filament had broken, the circuit would be open and neither bulb would light. Since one bulb does light, the path for current must still be complete. The most likely explanation is that the dark bulb has been short-circuited. This means an alternative very low resistance path (such as a wire touching both terminals of the bulb) bypasses the bulb, so almost no current flows through it. As a result, no light is produced.
在串联电路中，每个元件流过的电流相同。假如某个灯泡的灯丝断裂，电路就会断开，两个灯泡都不会亮。既然有一个灯泡亮起，说明电流通路仍是完整的。最可能的解释是，不亮的灯泡被短路了。这意味着存在一条极低电阻的替代路径（例如一根导线触碰了灯泡的两个接线端），绕过了该灯泡，因此几乎没有电流流过它。于是它不发光。
The student can test this idea by replacing the dark bulb with a bulb known to work. If the substitute bulb also stays dark, the fault lies elsewhere – perhaps the original bulb was okay, and a hidden short circuit remains. Checking for any stray wires touching both sides of the lamp holder would confirm the fault.
学生可以通过将一个已知完好的灯泡替换不亮的灯泡来验证这个想法。如果替换灯泡仍不亮，则故障在其他地方——可能原灯泡没问题，隐藏的短路仍然存在。检查是否有任何导线误触灯座的两端就能确认故障所在。
This case study shows that logical step-by-step testing is essential when troubleshooting circuits. Always check the simplest possibilities first before assuming a component is broken.
这个案例表明，在排除电路故障时分步逻辑测试至关重要。永远先检查最简单的可能性，而不是贸然认定某个元件损坏。
3. Case Study 3: Measuring Speed on a School Run | 案例三：测量上学途中的速度
Sam runs a straight 100 m stretch on the school field to train for sports day. His friend times him with a stopwatch: 14.0 seconds exactly. They want to work out his average speed.
萨姆在学校操场的笔直100米跑道上为运动会训练。他的朋友用秒表为他计时：恰好14.0秒。他们想计算出他的平均速率。
The formula that links distance, time, and speed is:
距离、时间和速率之间的关系式为：
speed = distance ÷ time
v = d ÷ t
Plugging in the numbers: d = 100 m, t = 14 s, so v = 100 ÷ 14 ≈ 7.14 m/s. Sam's average speed is about 7.1 metres per second.
代入数字：d=100 m，t=14 s，因此 v=100÷14≈7.14 m/s。萨姆的平均速率约为每秒7.1米。
Sam knows he sprinted faster over the first 50 m and slowed down near the end. Even though his speed changed, the calculated value represents the average speed for the whole journey. To find his speed at a particular instant (instantaneous speed), you would need a much more detailed record, such as a distance-time graph or video analysis.
萨姆知道自己在头50米跑得更快，接近终点时慢了下来。尽管他的速率在不断改变，计算所得的数值代表的是整个行程的平均速率。若要找出某一特定时刻的速率（瞬时速率），就需要更详细的记录，比如距离-时间图或视频分析。
This case study reinforces the importance of using the correct equation, paying attention to units (metres and seconds), and distinguishing between average and instantaneous speed.
该案例强化了使用正确公式、注意单位（米和秒）以及区分平均速率与瞬时速率的重要性。
4. Case Study 4: Designing a Thermos Flask | 案例四：设计保温瓶
A thermos flask keeps hot drinks hot for hours. How? The design cleverly minimises energy transfer by conduction, convection, and radiation. The flask has a double-walled glass container with a vacuum between the walls. Because a vacuum contains very few particles, conduction and convection cannot take place across this gap.
保温瓶能让热饮保温数小时。它是如何做到的呢？其设计巧妙地最小化了传导、对流和辐射带来的能量转移。保温瓶有一个双层玻璃容器，两层之间是真空。由于真空中几乎没有粒子，传导和对流都无法穿过这个空隙。
The glass walls are silvered, giving them a mirror-like finish. Shiny surfaces are poor radiators and poor absorbers of thermal radiation. This means very little heat is lost by radiation from the hot liquid inside, and very little is gained from the outside when the contents are cold.
玻璃壁镀有一层银，使其具有镜面般的光泽。光亮的表面是热辐射的不良发射体和吸收体。这意味着内部热液通过辐射散失的热量极少，当内容物是冷饮时，从外部吸收的热量也极少。
The stopper at the top is made of an insulating material such as cork or plastic, which is a poor conductor. It prevents convection currents from carrying warm air out of the flask. Together, these features trap most of the energy, keeping the temperature stable.
顶部的塞子由软木或塑料等绝热材料制成，它们是热的不良导体。它阻止对流气流将瓶内的暖空气带出。这些特性共同作用，把大量能量锁住，维持温度稳定。
Evaluating the thermos flask helps students see how understanding heat transfer allows engineers to design practical solutions. The case links particle theory (vacuum stops particles), reflection (silvered surfaces), and material properties.
评估保温瓶可以帮助学生认识到，理解了热传递后，工程师们便能设计出实用的解决方案。该案例联系了粒子理论（真空阻止粒子运动）、反射（镀银表面）和材料特性。
5. Case Study 5: Using Echoes to Measure Distance | 案例五：利用回声测量距离
A hiker stands in front of a tall cliff and claps his hands loudly. Exactly 2.0 seconds later, he hears the echo. The speed of sound in air is approximately 340 m/s. How far away
Published by TutorHao | Year 7 Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图