📚 Case Study Practical Exercises in Year 7 Physics | 七年级物理案例分析实战演练
Welcome to this case study workshop! In Year 7 physics, you learn many fascinating concepts about motion, forces, energy, electricity, waves, and matter. The best way to deepen your understanding is to apply these ideas to real-life situations. This resource presents 10 practical investigation scenarios, each containing key observations, sample calculations, and reflection questions. Work through them step by step and test your science skills.
欢迎来到本次案例分析实战演练！在七年级物理中，你学习了许多关于运动、力、能量、电、波和物质的有趣概念。加深理解的最佳方法是将这些想法应用到实际情境中。本文提供10个实践探究场景，每个都包含关键观察、示例计算和反思问题。请逐步完成并测试你的科学技能。
1. Measuring Speed: The 50-Metre Sprint | 测量速度：50米短跑
using a trundle wheel. Have a friend sprint along the track while you record the time with a digital stopwatch to the nearest 0.1 s. The formula you will use is: average speed = total distance / total time. In symbols, v = d / t.
要计算平均速度，你需要两个测量值：总路程和花费的总时间。使用测轮在学校操场上标出一条50米的直线跑道。请一位朋友沿着跑道冲刺，同时你用数字秒表记录时间，精确到0.1秒。所用公式为：平均速度 = 总距离 / 总时间。符号表示为 v = d / t。
/s (rounded to one decimal place). This does not tell us about the instantaneous speed at each moment. To improve accuracy, you could repeat the trial three times and calculate the mean. Always remember to align your eye perpendicular to the finish line to avoid reaction-time errors.
示例：一名学生用8.2秒跑完50米。他的平均速度为 50 m / 8.2 s ≈ 6.1 m/s（保留一位小数）。这并未告诉我们每一时刻的瞬时速度。为了提高精确度，你可以重复测量三次并计算平均值。务必记住眼睛要与终点线垂直对齐，以避免反应时间误差。
Reflection: Would the average speed be higher if the runner started from a standing position compared to a rolling start? Suggest one way to measure instantaneous speed more directly.
反思：如果跑者从站立状态起跑与行进间起跑相比，平均速度会更高吗？请提出一种更直接测量瞬时速度的方法。
2. Investigating Friction: Toy Car on Different Surfaces | 探究摩擦力：不同表面上的玩具车
Set up a shallow ramp and release a toy car from the same height each time. Let it roll onto horizontal surfaces covered with different materials: polished wood, carpet, and coarse sandpaper. Use a metre ruler to measure how far the car travels before it stops. The surface that stops the car earliest exerts the greatest friction force.
搭建一个浅坡道，每次从相同高度释放一辆玩具车。让它滑行到铺有不同材料的水平表面上：抛光的木材、地毯和粗糙的砂纸。用米尺测量汽车停止前行驶的距离。最早让汽车停下的表面施加的摩擦力最大。
Your data table should include columns for surface type, distance travelled (cm), and a ranking of friction from highest to lowest. From the results, you will see that sandpaper produces the highest friction, causing the shortest stopping distance. Wood gives the lowest friction, allowing the longest glide. To make this a fair test, you must keep the car, the ramp angle, and the release point identical.
你的数据表格应包含表面类型、行驶距离（厘米）和摩擦力从高到低的排名。从结果中你会发现，砂纸产生的摩擦力最大，导致停车距离最短；木材的摩擦力最小，滑行距离最长。为了公平测试，你必须保持小车、坡道角度和释放点完全相同。
Challenge: Predict what would happen if you oiled the wood surface. Explain your prediction using the idea of friction.
挑战：如果你在木表面上涂油，会发生什么？请用摩擦力的概念解释你的预测。
3. Stretching Springs: Exploring Hooke's Law | 弹簧拉伸：探索胡克定律
ime, recording the new length each time. The extension is found by: extension = new length – original length. Plot a graph of force (N) against extension (cm).
将一根轻质弹簧悬挂在铁架台上并附上指针。测量无负载时的原始长度。然后每次增加一个0.5 N的砝码，记录每次的新长度。伸长量由下式得出：伸长量 = 新长度 – 原始长度。绘制力（N）与伸长量（cm）的关系图。
For a spring obeying Hooke's Law, the graph is a straight line passing through the origin. This tells us that extension is directly proportional to the applied force, provided the elastic limit is not exceeded. If you add too much weight, the spring will permanently deform and the line will curve.
对于遵从胡克定律的弹簧，图线是一条通过原点的直线。这说明只要不超过弹性限度，伸长量与施加的力成正比。如果添加过重的砝码，弹簧将永久变形，图线也会弯曲。
Safety note: Always wear goggles and place a cushion below heavy loads. Q: A spring stretches 3 cm with a 2 N load. What force would cause an extension of 7.5 cm?
安全提示：始终佩戴护目镜，并在重物下放置缓冲垫。问：某弹簧在2 N负载下伸长3 cm。要使伸长量达到7.5 cm，需要多大的力？
4. Series Circuits and Bulb Brightness | 串联电路与灯泡亮度
Build a simple circuit using one 1.5 V cell, one lamp, and connecting wires. Observe the brightness. Then insert a second identical lamp in series with the first one. You will notice both bulbs glow much dimmer than the single bulb did.
使用一个1.5 V电池、一个灯泡和导线搭建简单电路。观察灯泡亮度。然后在电路中串联第二个相同的灯泡。你会发现两个灯泡都比单个灯泡时暗得多。
Adding more bulbs increases the total resistance of the circuit, which reduces the current flowing from the cell. Since each bulb shares the same current in a series circuit, they receive less energy per second and become dimmer. If you add a third bulb, the brightness drops further. Unlike a parallel circuit, where each bulb receives the full cell voltage, series bulbs behave like runners sharing one scarf.
增加更多灯泡会增大电路的总电阻，从而减小来自电池的电流。由于串联电路中每个灯泡共享相同的电流，它们每秒获得的能量减少，因此变暗。如果再添加第三个灯泡，亮度会进一步下降。与并联电路不同（并联电路中每个灯泡获得全电压），串联灯泡就像几名跑步者共用一条围巾。
Design task: Draw a circuit diagram with two bulbs in series and one switch that controls both. Add an ammeter symbol to show where you would measure current.
设计任务：画出两盏灯泡串联和一个开关控制两者的电路图。添加一个电流表符号，以显示你会从哪里测量电流。
5. Reflection of Light: Investigating the Law of Reflection | 光的反射：探究反射定律
Place a plane mirror along a straight line on a sheet of white paper. Shine a narrow ray of light from a ray box so that it strikes the mirror at a single point. Trace the incident ray and the reflected ray with a sharp pencil. Draw the normal – a dashed line perpendicular to the mirror at the point of incidence. Use a protractor to measure the angle of incidence, i, and the angle of reflection, r.
将平面镜沿一条直线放在白纸上。用光线盒发出一束窄光，使光线照射到镜面上的一点。用尖铅笔描出入射光线和反射光线。画出法线——在入射点处与镜面垂直的虚线。用量角器测量入射角 i 和反射角 r。
ormal lie in the same plane. Try varying the incident angle and verify the law each time. This principle is used in periscopes and optical illusions.
你将始终发现入射角等于反射角（i = r）。两条光线和法线位于同一平面内。尝试改变入射角并每次都验证这一定律。该原理被用于潜望镜和光学幻象中。
Extension: What happens when you use a curved mirror? Briefly investigate with a concave mirror and describe your observations.
拓展：当你使用曲面镜时会发生什么？用凹面镜进行简单探究并描述你的观察结果。
6. Sound Travels Through Solids: The String Telephone | 声音通过固体传播：绳电话
Create a simple string telephone by poking a small hole in the base of two paper cups and threading a 10-metre long cotton string through them. Tie knots inside the cups so the string stays in place. When one person speaks into a cup while the string is taut, the second person can hear the message clearly through the other cup.
制作一个简单的绳电话：在两个纸杯底部各扎一个小孔，穿入一根10米长的棉线，在杯内打结固定。当线被拉紧，一个人对着一个杯子说话时，另一个人可以通过另一个杯子清晰地听到信息。
The sound vibrations from your voice transfer to the cup, which passes them along the string as mechanical vibrations. Because the particles in a solid (the string) are packed tightly together, vibrations travel faster and with less energy loss than in air. This is why the sound is louder and clearer through the string telephone than simply shouting across the same distance.
你说话的声音振动传递到杯子，杯子再将它们作为机械振动沿线传递。由于固体（线）中的粒子排列紧密，振动比在空气中传播得更快且能量损失更少。这就是为什么通过绳电话听到的声音比直接喊话更响亮、更清晰。
Does the string telephone work if the string is slack? Explain using ideas about energy transfer through particles.
如果线是松弛的，绳电话还能工作吗？请用粒子间能量传递的观点解释。
7. Visualising Magnetic Fields with Iron Filings | 用铁屑可视化磁场
Place a bar magnet flat on a table and cover it with a thin sheet of paper or transparency. Gently sprinkle a light dusting of iron filings over the paper. Tap the paper very carefully and watch the filings arrange themselves into lines that curve from the north pole to the south pole. This is the magnetic field pattern.
将条形磁铁平放在桌上，用一张薄纸或透明塑料片盖住。在上面轻轻撒上一层铁屑。小心地敲击纸张，观察铁屑排列成从北极指向南极的曲线。这就是磁场图案。
The lines are closest together near the poles, indicating that the magnetic field is strongest there. You can also investigate what happens when two like poles (e.g. north facing north) are brought close together. The filings will reveal a neutral point where the two fields cancel each other, showing no magnetic force.
磁极附近的线条最密集，表明此处磁场最强。你还可以探究两个同名磁极（如北极对北极）靠近时的情形。铁屑会显示出一个中性点，在此处两个磁场互相抵消，显示没有磁力作用。
Placing a compass at various points allows you to check the direction of the field lines. Q: What would the pattern look like between two opposite poles placed side by side?
在不同位置放置指南针可以检验磁场线的方向。问：两个磁极并排对置（N对S）时，图案会是什么样？
8. Density and Buoyancy: Sink or Float? | 密度与浮力：沉还是浮？
lume. Measure the mass of an object on a digital balance (grams). For regular solids, calculate volume by multiplying length x width x height. For irregular objects, use the displacement method in a measuring cylinder.
物质的密度告诉我们给定体积内包含多少质量。使用公式：密度 = 质量 / 体积。用数字天平测量物体的质量（克）。对于规则固体，通过长×宽×高计算体积。对于不规则物体，使用量筒中的排水法测量体积。
Water has a density of 1 g/cm³. An object with a density less than 1 g/cm³ will float: a wax candle (~0.9 g/cm³) and an ice cube (~0.92 g/cm³) both float. A stone (~2.5 g/cm³) sinks because its density is greater than that of water. Even a gigantic ship floats because its overall density (including the air inside) is less than water's density.
水的密度为1 g/cm³。密度小于1 g/cm³的物体会漂浮：蜡烛（约0.9 g/cm³）和冰块（约0.92 g/cm³）都会浮起。石头（约2.5 g/cm³）沉底是因为其密度大于水。即使是巨型轮船也能漂浮，因为它的整体密度（包括内部空气）小于水的密度。
Task: A silver-coloured cube has a mass of 21 g and a side length of 3 cm. Calculate its volume and density. Based on its density, is it likely made of aluminium (2.7 g/cm³) or steel (7.8 g/cm³)?
任务：一个银色立方体质量为21 g，边长为3 cm。计算它的体积和密度。根据密度，它可能是铝（2.7 g/cm³）还是钢（7.8 g/cm³）？
9. Energy Transformations: The Bouncing Ball | 能量转换：弹跳球
energy (KE). Just before impact, the ball has maximum KE. The equation relating GPE to height is: GPE = mass x gravitational field strength x height, but for Year 7 we focus on the energy chain.
将橡胶球举离地面一定高度并释放。下坠过程中，重力势能（GPE）转化为动能（KE）。撞击前瞬间，球的动能最大。GPE与高度的关系式为：GPE = 质量 × 重力场强 × 高度，但七年级我们重点关注能量链。
When the ball hits the floor, it deforms and some energy is stored elastically. As it rebounds, that energy is converted back to kinetic and then to gravitational potential. However, the ball never rises to its original height because some energy is transferred to thermal energy (heating the ball and the surface) and sound. Each successive bounce gets lower.
当球撞击地面时，它发生形变，部分能量以弹性势能的形式储存。反弹时，这份能量又转回动能，再转为重力势能。但是球永远不会回到原来的高度，因为部分能量转移为热能（加热球和接触面）和声能。每次弹跳高度都会降低。
Investigate: Drop the ball from 100 cm and measure the rebound height. Calculate the percentage of energy retained as (rebound height / drop height) x 100. Test on different surfaces such as concrete and carpet.
探究：将球从100 cm高释放，测量反弹高度。计算保留能量的百分比：(反弹高度 / 释放高度) × 100。在混凝土地面和地毯等不同表面上进行测试。
10. Thermal Insulators: Keeping It Hot | 热绝缘体：保温
Pour equal volumes of hot water (same starting temperature, e.g. 70 °C) into identical beakers. Wrap each beaker in a different insulating material: aluminium foil, wool cloth, bubble wrap newspaper, and leave one unwrapped as a control. Record the temperature every 2 minutes for 20 minutes using a thermometer.
将等体积、相同起始温度（如70 °C）的热水倒入多个相同的烧杯中。每个烧杯用不同的隔热材料包裹：铝箔、羊毛布、气泡膜和报纸，留一个不包裹作为对照组。用温度计每2分钟记录一次温度，持续20分钟。
Identify the best insulator as the material that allows the slowest temperature drop. Wool performs very well because it traps air, and still air is a poor conductor of heat. Foil helps by reflecting radiant heat back towards the water. This is why survival blankets are shiny – they reduce heat loss through radiation.
最好的隔热材料是让温度下降最慢的那种。羊毛表现很好，因为它能困住空气，而静止的空气是热的不良导体。铝箔则通过将辐射热反射回水中提供帮助。这就是为什么求生毯是闪亮的——它们减少辐射热损失。
Final challenge: Draw a bar chart of the temperature drop after 20 minutes for each material. Explain why you should start with the same volume and initial temperature. How would a styrofoam cup compare?
最终挑战：绘制每种材料20分钟后温度下降的条形图。解释为什么开始时必须用相同体积和相同初始温度。泡沫塑料杯的表现会如何？
Published by TutorHao | Physics Revision Series | aleveler.com
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