📚 Year 7 WJEC Physics: Case Studies in Action | 案例分析与实战演练
Physics isn't just about textbooks—it's all around us. This case study collection explores real-world situations to help Year 7 students apply core principles from the WJEC curriculum, from measuring speed to designing circuits. Each case breaks down the problem, highlights the key physics, and offers step-by-step solutions.
物理不只是教科书里的知识——它就在我们身边。本系列案例分析通过真实情境帮助七年级学生应用WJEC课程的核心原理，从测量速度到设计电路。每个案例分解问题、突出关键物理概念并提供逐步解决方案。
1. Measuring Speed: A Sprinter's Challenge | 测量速度：短跑运动员的挑战
In a school sports day, a student runs 100 metres in 14.2 seconds. What is her average speed? Let's use the speed formula and then check if she could outrun a bicycle moving at 6 m/s.
在学校运动会中，一名学生用14.2秒跑完100米。她的平均速度是多少？我们用速度公式计算，并检查她能否超过以6米/秒行驶的自行车。
The equation for average speed is:
平均速度的公式为：
average speed = total distance ÷ total time
00 m, time = 14.2 s. So speed = 100 m / 14.2 s ≈ 7.04 m/s. This is faster than the bicycle's 6 m/s, so yes, she would win over a short distance.
代入数值：距离 = 100 米，时间 = 14.2 秒。因此速度 = 100 m / 14.2 s ≈ 7.04 m/s。这比自行车的6 m/s快，所以她在短距离内会胜出。
Key point: average speed assumes constant motion; in a real sprint, the runner starts from zero and accelerates, so her maximum speed is even higher.
要点：平均速度假设匀速运动；在实际冲刺中，运动员从零开始加速，因此她的最大速度甚至更高。
2. Friction at the Skate Park | 摩擦力在滑板公园
A skateboarder rolls down a ramp and glides to a stop on a flat surface. Why does he slow down? The answer is friction. Without it, he would keep moving forever according to Newton's first law.
滑板手从斜坡上滑下，在平坦地面滑行一段后停下。为什么他会减速？答案是摩擦力。如果没有摩擦力，根据牛顿第一定律，他会永远运动下去。
We can reduce friction by polishing the bearings or using smoother wheels; increase friction by applying a rough grip tape to the deck. In wet conditions, friction drops, which can be dangerous for braking.
我们可以通过抛光轴承或使用更光滑的轮子来减小摩擦；在板面上粘贴粗糙的防滑砂纸来增大摩擦。在潮湿条件下摩擦会减小，这对刹车很危险。
Design challenge: If you want the skateboard to stop in exactly 5 metres after leaving the ramp, what factors affect that distance? Weight, surface texture, and speed all matter.
设计挑战：如果想让滑板离开斜坡后正好在5米内停下，哪些因素会影响距离？重量、表面粗糙度和速度都很重要。
3. Gravity and Weight: Lunar Jumping | 重力与重量：月球跳跃
oon, gravity is only 1.6 N/kg. How much would she weigh there, and how high could she jump?
在地球上，一名质量为80公斤的宇航员体重约为800牛顿（取 g=10 N/kg）。在月球上，重力只有1.6 N/kg。她在那里多重，能跳多高？
Weight on Moon = mass × gravitational field strength = 80 kg × 1.6 N/kg = 128 N. That's about one-sixth of her Earth weight. Because her legs can exert the same force, she'd be able to jump roughly six times higher, ignoring the bulky suit!
月球上的重量 = 质量 × 重力场强 = 80 kg × 1.6 N/kg = 128 N，大约是她地球重量的六分之一。因为她的腿部力量不变，她可以跳大约六倍高（不考虑笨重的太空服）。
This case shows the difference between mass (constant) and weight (depends on gravity). Always use the correct units: mass in kg, weight in N.
这个案例展示了质量（恒定）和重量（取决于重力）的区别。始终使用正确单位：质量用千克，重量用牛顿。
4. Sound Transmission: Designing Soundproof Headphones | 声音传播：设计隔音耳机
You want to block the noise of a busy classroom to focus on your music. Sound travels as vibrations through a medium. How can we stop it? The answer lies in absorption and reflection.
你想阻隔喧闹教室的噪音，专心听音乐。声音以振动形式通过介质传播。我们如何阻止它？答案在于吸收和反射。
Materials like soft foam absorb sound energy, while hard, smooth surfaces reflect it. For headphones, engineers use layers: a dense outer shell to reflect external noise, and soft padding inside to absorb any remaining vibrations. This is why ear cushions are made of memory foam.
软泡沫等材料吸收声能，而坚硬光滑的表面反射声能。对于耳机，工程师使用层状结构：致密的外壳反射外部噪音，内部的柔软衬垫吸收剩余的振动。这就是耳罩采用记忆海绵的原因。
Test case: If a sound wave has a frequency of 440 Hz, can a material that vibrates naturally at 440 Hz help? Yes, it can resonate, but for blocking sound we want materials that don't resonate with the unwanted noise.
测试案例：如果一个声波频率为440 Hz，那么自然振动频率也为440 Hz的材料会有帮助吗？是的，它会发生共振，但为了阻隔声音，我们希望材料不与不需要的噪音共振。
5. Reflection of Light: Building a Periscope | 光的反射：制作潜望镜
ect to your eye, applying the law of reflection: angle of incidence = angle of reflection.
潜望镜可以让你看到墙后的情景。它使用两面与水平面成45°角的平面镜。画出来自物体的光线到达眼睛的路径，应用反射定律：入射角等于反射角。
Case: A toy periscope is 30 cm long. Where should you place the mirrors? They must be parallel and face each other. The light enters the top, hits the first mirror, reflects down, hits the second, and reflects horizontally into your eye. Measure the angles — each reflection turns the ray by 90°.
案例：一个玩具潜望镜长30厘米。镜子应该放在哪里？它们必须平行且相对。光线从顶部进入，击中第一面镜子，向下反射，击中第二面，再水平反射入眼睛。测量角度——每次反射使光线偏转90°。
Extension: How does a mirror image differ from the real object? It is laterally inverted (left becomes right). In a periscope, the final image is not inverted because of the double reflection.
延伸：镜像与真实物体有何不同？它是横向反转的（左右互换）。在潜望镜中，由于两次反射，最终图像不是反向的。
6. Electric Circuits: Designing a Torch | 电路：设计手电筒
A basic torch has a cell (battery), a switch, and a bulb. If the bulb is rated 2.5 V and the cell is 1.5 V, how could you power it? You need two cells in series to supply 3.0 V (a bit higher, but acceptable with a resistor). Let's analyse.
一个基本的手电筒包含一个电池、一个开关和一个灯泡。如果灯泡额定电压为2.5V，而电池是1.5V，你如何供电？你需要两节电池串联提供3.0V（略高，但可以加电阻）。我们来分析。
allenge: If the bulb has a resistance of 10 Ω and the supply is 3.0 V, what is the current? Using Ohm' V / R = 3.0 V / 10 Ω = 0.3 A. Now calculate the power: P = V × I = 3.0 V × 0.3 A = 0.9 W.
电路挑战：如果灯泡电阻为10 Ω，电源为3.0 V，电流是多少？使用欧姆定律：I = V / R = 3.0 V / 10 Ω = 0.3 A。现在计算功率：P = V × I = 3.0 V × 0.3 A = 0.9 W。
Safety note: Too much current would blow the bulb. That's why fuses are important. A fuse melts and breaks the circuit if the current exceeds a safe value.
安全提示：电流过大 会烧坏灯泡。因此保险丝很重要。如果电流超过安全值，保险丝会熔断并断开电路。
Diagram practice: Draw the circuit using symbols: cell, switch, lamp, connecting wires. Ensure the switch is open in the 'off' position.
绘图练习：用符号画出电路：电池、开关、灯泡、导线。确保开关在“关”位置时是断开的。
7. Energy Transfers: Roller Coaster Physics | 能量转换：过山车物理
At the top of the first hill, a roller coaster car has maximum gravitational potential energy (GPE). As it plunges down, GPE changes into kinetic energy (KE). Ignoring friction, the total energy stays constant.
在第一个上坡顶部，过山车具有最大重力势能(GPE)。随着它俯冲而下，GPE转化为动能(KE)。忽略摩擦，总能量保持不变。
000 J. Use KE = ½mv² to find speed: 100,000 = ½ × 500 × v² => v² = 400 => v = 20 m/s. That's about 72 km/h!
案例：一辆质量500公斤的车在20米高度。GPE = mgh = 500 × 10 × 20 = 100,000 J。在底部，所有GPE转化为KE。所以KE = 100,000 J。用 KE = ½mv² 求速度：100,000 = ½ × 500 × v² => v² = 400 => v = 20 m/s。这大约72 km/h！
In reality, some energy is lost as heat due to friction and air resistance. Engineers design the track to minimise these losses and ensure a thrilling but safe ride.
实际中，部分能量因摩擦和空气阻力而转化为热量损失。工程师设计轨道以尽量减少这些损失，确保既刺激又安全。
8. Magnetism: Maglev Trains | 磁性：磁悬浮列车
Maglev trains use magnetic repulsion to float above the track, eliminating friction. The track and the train have powerful electromagnets. Like poles repel, lifting the train.
磁悬浮列车利用磁力排斥使其悬浮于轨道上方，消除摩擦。轨道和列车都有强大的电磁铁。同极相斥，将列车抬起。
Investigation: You have two permanent bar magnets. How can you arrange them to produce levitation? Place one magnet on a scale, north pole up. Hold another above it, north pole down. The scale reading decreases as the top magnet repels the bottom one, demonstrating a smaller apparent weight.
探究：你有两块永磁条。如何安排它们产生悬浮？将一块磁铁放在秤上，北极朝上。另一块持于上方，北极朝下。当上方磁铁排斥下方磁铁时，秤的读数减小，显示出较小的表观重量。
This case also connects to electromagnets: by controlling the current, the magnetic force can be adjusted, allowing precise height control in real maglev systems.
本例也与电磁铁相关：通过控制电流，可以调节磁力，实现真实磁悬浮系统的精确高度控制。
Challenge: If the train weighs 300 kN, what magnetic force is needed? An upward force of at least 300 kN to balance weight, plus extra for acceleration.
挑战：如果列车重300 kN，需要多大磁力？至少需要向上的300 kN来平衡重量，外加额外力量用于加速。
9. Density: Why Ships Float and Coins Sink | 密度：为何船能浮而硬币会沉
A steel coin sinks, yet a massive steel ship floats. The key is density and shape. The coin's average density is greater than water, so it sinks. The ship, though made of steel, contains mostly air, making its overall density less than water.
钢质硬币会沉没，而巨大的钢船却能浮起。关键在于密度和形状。硬币的平均密度大于水，所以下沉。船虽然由钢制成，但内部大部分是空气，使其整体密度小于水。
= mass / volume. A coin with mass 10 g and volume 1.2 cm³ has density ≈ 8.33 g/cm³. Water' es (10⁸ kg) to float, it must displace a volume of water equal to its weight, roughly 100,
Published by TutorHao | Year 7 Physics Revision Series | aleveler.com
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