📚 Year 7 CIE Physics: Case Study Practice Exercises | Year 7 CIE 物理：案例分析实战演练
Welcome to this case study practice session for Year 7 CIE Physics. In this article, we will explore real-world scenarios to strengthen your understanding of forces, energy, waves, electricity, and more. Each case study presents a situation, asks you to think like a scientist, and then explains the underlying physics clearly.
欢迎参加 Year 7 CIE 物理案例分析实战。本文将探究真实场景，强化你对力、能量、波、电等概念的理解。每个案例提出一个情境，让你像科学家一样思考，然后清楚解释其中的物理原理。
1. The Stalled Car and Push Force | 熄火的汽车和推力
A car has run out of fuel and is stuck on a flat road. Two people start to push it from behind.
一辆汽车燃油耗尽，停在平坦路面上。两个人从后面开始推车。
Observation: At first the car is very difficult to move, but once it starts rolling, it becomes easier to keep it moving.
观察：起初车很难推动，但一旦车开始滚动，保持它移动变得更容易。
Why is the car difficult to move at the start? Because static friction between the tyres and the road is high. To overcome this initial friction, the people need to apply a large force.
为什么车一开始难推动？因为轮胎与路面之间的静摩擦力很大。为了克服初始摩擦，人们需要施加很大的力。
Once the car moves, kinetic friction (rolling friction) takes over, which is smaller than static friction. Also, the car has gained momentum, so it's easier to push.
一旦汽车运动起来，动摩擦（滚动摩擦）起作用，它比静摩擦小。同时汽车获得了动量，所以更容易推。
This case shows the difference between static friction and kinetic friction.
这个案例展示了静摩擦与动摩擦的区别。
2. Measuring Average Speed of a Toy Car | 测量玩具车的平均速度
A student releases a toy car from the top of a ramp. She measures the time it takes to travel different distances along the floor after leaving the ramp.
一名学生从斜面顶部释放一辆玩具车。她测量小车离开斜面后沿地面运动不同距离所用的时间。
Here are her measurements:
她的测量数据如下：
| Distance (m) | Time (s) | Average speed (m/s) |
|---|---|---|
| 1.0 | 2.0 | 0.5 |
| 2.0 | 3.6 | 0.56 |
| 3.0 | 5.0 | 0.60 |
The average speed is calculated using the formula:
用以下公式计算平均速度：
speed = distance / time
Notice that the speed decreases slightly, likely due to friction from the floor.
注意到速度略微下降，可能是由于地面的摩擦力。
If the floor were frictionless, the car would travel at constant speed and infinite distance, according to Newton's first law of motion.
如果地面没有摩擦力，根据牛顿第一运动定律，小车将保持匀速并永远运动下去。
3. Why a Safety Helmet Is Covered in Foam | 为什么安全头盔覆盖泡沫
When you fall off a bicycle, your head hits the ground. A helmet protects your head because it contains a thick layer of foam material.
当你从自行车上摔下，头部撞击地面。头盔保护头部，因其含有一层厚厚的泡沫材料。
The foam is soft and can be compressed. When your head hits something hard, the foam compresses over a slightly longer time, reducing the force of impact.
泡沫柔软且可压缩。当头部撞到硬物，泡沫在稍长的时间里压缩，减小了冲击力。
In physics, force is related to the change in momentum over time. By increasing the time of impact, the average force decreases. This is the same principle airbags use.
在物理中，力与动量随时间的变化有关。通过增加撞击时间，平均力减小。这与安全气囊原理相同。
Year 7 students can understand it as: the foam absorbs some of the kinetic energy and spreads the force over a larger area, so the pressure on your head is lower.
七年级学生可理解为：泡沫吸收部分动能，并将力分散到更大面积，因此头部受到的压强更小。
4. Series Circuit: One Bulb Goes Out | 串联电路：一个灯泡熄灭
Sarah builds a series circuit with two bulbs and a battery. Both bulbs light up normally. Then one bulb burns out and its filament breaks.
莎拉用两盏灯泡和一节电池搭建了一个串联电路。两盏灯正常发光。随后一盏灯泡烧坏，灯丝断开。
Immediately after the filament breaks, the other bulb also goes out. Why?
灯丝断开后，另一盏灯泡也立即熄灭。为什么？
In a series circuit, there is only one complete loop for the current to flow. If any part of the loop breaks, the circuit becomes open (incomplete) and current stops everywhere.
在串联电路中，电流只有一条完整的回路。如果回路中任何一处断开，电路就成为开路（不完整），所有地方的电流都停止。
If Sarah wanted to keep one bulb on even if the other fails, she should connect them in parallel. Then each bulb has its own separate path to the battery.
如果莎拉希望一盏灯泡故障时另一盏还能亮，应该把灯泡并联。这样每盏灯泡都有自己独立通往电池的路径。
5. Conduction in a Metal Spoon | 金属勺中的热传导
When you put a metal spoon into a hot cup of tea, the handle gradually becomes warm. How does the heat transfer from the tea to your hand?
当你把金属勺放入一杯热茶，勺柄会逐渐变热。热量如何从茶传递到你的手？
Metals are good conductors of heat. Free electrons inside the metal gain kinetic energy from the hot end and collide with neighboring particles, passing the energy along the spoon.
金属是热的良导体。金属内的自由电子从热端获得动能，并与邻近粒子碰撞，把能量沿着勺传递。
This process is called conduction. Materials like wood or plastic are insulators; they do not have freely moving electrons, so they feel cooler to the touch.
这个过程叫传导。像木头或塑料等材料是绝缘体；它们没有自由移动的电子，所以摸上去感觉更凉。
Year 7 students should be able to identify conductors and insulators in everyday life, such as metal pans (conductor) and wooden handles (insulator).
七年级学生应能识别日常生活中的导体与绝缘体，如金属锅（导体）和木手柄（绝缘体）。
6. Sound Higher Pitched with a Short Ruler | 短尺子发出更高音调的声音
A student holds a plastic ruler on the edge of a desk so that a part of it sticks out. She flicks the free end and hears a sound. She then changes the length of the ruler sticking out.
一个学生把一把塑料尺按在桌边，使一部分
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