📚 Year 7 Cambridge Physics: In-Depth Past Paper Analysis | 剑桥Year 7物理：历年真题深度解析
Past papers are one of the most effective tools for mastering Cambridge Year 7 Physics. By working through real exam questions, you can identify recurring themes, test your understanding of key concepts, and build the confidence needed for the Checkpoint test. In this article, we will walk through the most common topics that appear in past papers, break down typical question styles, and show you exactly how to structure your answers for full marks.
历年真题是掌握剑桥 Year 7 物理最有效的方法之一。通过练习真实考题，你可以发现反复出现的主题，检验自己对核心概念的理解，并为 Checkpoint 考试建立信心。本文将梳理真题中最常见的主题，拆解题型，并展示如何组织答案以拿到满分。
1. Scientific Enquiry and Measurement | 科学探究与测量
ed to read the volume of water in a measuring cylinder, record the length of a spring from a photograph, or convert 500 g into kilograms. Always keep these conversions in mind: 1 kg = 1000 g, 1 m = 100 cm, 1 minute = 60 seconds. Using the correct unit is just as important as the numerical value.
许多真题一开始会考查你读取仪器示数、换算单位以及识别变量的能力。比如，你可能需要读出量筒中水的体积，从照片上记录弹簧长度，或将500克换算成千克。请始终记住这些换算关系：1千克=1000克，1米=100厘米，1分钟=60秒。使用正确的单位与数值同样重要。
| Quantity (量) | Common conversion (常用换算) |
|---|---|
| Mass (质量) | 1 kg = 1000 g |
| Length (长度) | 1 m = 100 cm = 1000 mm |
| Time (时间) | 1 min = 60 s |
| Volume (体积) | 1 litre = 1000 ml = 1000 cm³ |
When planning an investigation, you must identify the independent variable (what you change), the dependent variable (what you measure), and the control variables (what you keep the same). A classic past paper task says: 'Suggest one variable that should be controlled in this investigation.' Typical answers include the starting temperature, the volume of water, or the type of material used.
在设计探究实验时，你必须识别出自变量（你改变的变量）、因变量（你测量的变量）和控制变量（你保持不变的量）。真题中常见的要求是：“提出一个在该探究中应控制的变量。” 典型答案包括起始温度、水的体积或所用材料的种类。
2. Understanding Forces | 理解力
Exam questions frequently show a diagram of a book on a table, a boat floating, or a parachutist falling, and ask you to label the forces with arrows. Recognise these key forces: weight (always acting downwards), upthrust (upwards in fluids), friction or air resistance (opposing motion), and tension (pull along a rope). Forces are measured in newtons (N) and are represented by arrows whose length indicates the magnitude of the force.
考试题经常会展示书放在桌上、小船漂浮或跳伞者下落的示意图，并要求用箭头标出力的方向。请识别以下关键力：重力（总是竖直向下）、浮力（在流体中向上）、摩擦力或空气阻力（与运动方向相反）以及拉力（沿绳子方向）。力以牛顿（N）为单位，用箭头表示，箭头的长度表示力的大小。
When forces on an object are balanced, it stays still or moves at a constant speed. When forces are unbalanced, the object accelerates in the direction of the resultant force. Past papers may ask you to calculate the resultant force from two opposing arrows: for instance, a 10 N push to the right and 4 N friction to the left give a resultant force of 6 N to the right. Always state both the size and the direction.
当物体受到的力平衡时，它会保持静止或匀速直线运动。当力不平衡时，物体会沿合力的方向加速。真题可能会要求你计算两个方向相反的箭头产生的合力：例如，向右的10 N推力与向左的4 N摩擦力，合力为向右的6 N。一定要同时写出大小和方向。
resultant force = 10 N − 4 N = 6 N to the right
合力 = 10 N − 4 N = 6 N，方向向右
3. Speed and Distance-Time Graphs | 速度与距离-时间图
Speed is a measure of how quickly something moves, and you calculate it with the simple formula shown below. In distance-time graphs, time is plotted on the horizontal axis and distance on the vertical axis. A straight sloping line shows constant speed; a horizontal line means the object is stationary. The steeper the slope, the higher the speed. Many past papers present a graph and ask you to describe the motion or to calculate the speed during one section.
速度用来衡量物体运动的快慢，可以用下面这个简单公式计算。在距离-时间图中，时间标在横轴，距离标在纵轴。一条倾斜的直线表示匀速运动；水平线表示物体静止。斜率越陡，速度越大。许多真题会给出图线，并要求你描述一段运动或计算其中一段的速度。
speed = distance ÷ time
速度 = 距离 ÷ 时间
ng and include the unit, m/s. If the question asks for speed in km/h, you must convert first (5 m/s = 18 km/h, but Year 7 usually stays in m/s). When reading the slope from a graph, choose two clear points and find the change in distance divided by the change in time.
例题：一名自行车运动员在30秒内行驶了150米。计算平均速度。直接代入数字：速度 = 150 m ÷ 30 s = 5 m/s。一定要写出计算步骤并带上单位 m/s。如果题目要求以 km/h 为单位，你需要先进行换算（5 m/s = 18 km/h），不过 Year 7 通常以 m/s 为主。从图上读取斜率时，选取两个清晰的点，用距离的变化量除以时间的变化量即可。
4. Mass and Weight | 质量与重量
Mass and weight are often confused, but understanding their difference is a common exam focus. Mass is the amount of matter in an object, measured in kilograms (kg), and it stays the same everywhere in the universe. Weight is the force with which gravity pulls on that mass, measured in newtons (N), and it changes depending on the gravitational field strength. On Earth, the gravitational field strength is approximately 10 N/kg.
质量和重量常常被混淆，而理解它们的区别是常见的考试重点。质量是物体所含物质的多少，以千克（kg）为单位，在宇宙中任何地方都保持不变。重量是重力对物体的拉力，以牛顿（N）为单位，它会随引力场强度的变化而改变。地球表面的引力场强度大约是 10 N/kg。
weight (N) = mass (kg) × 10 N/kg
重量（N）= 质量（kg）× 10 N/kg
A typical past paper question asks: 'An astronaut has a mass of 75 kg on Earth. What is her mass on the Moon?' The correct answer is still 75 kg, because mass does not change. Then it might ask: 'What is her weight on the Moon if the Moon's gravity is 1.6 N/kg?' he weight is smaller on the Moon because gravity is weaker, even though her body is made of the same amount of material.
一道典型的真题会问：“一名宇航员在地球上的质量是75 kg，她在月球上的质量是多少？”正确答案仍然是75 kg，因为质量不会改变。接下来可能追问：“如果月球引力为1.6 N/kg，她在月球上的重量是多少？” 重量 = 75 × 1.6 = 120 N。要解释月球上的重量更小是因为引力更弱，即使她的身体由同样多的物质构成。
5. Density and the Particle Model | 密度与粒子模型
Density tells us how tightly matter is packed into a given volume. The formula connects mass and volume. Solids usually have high densities because particles are packed closely together; liquids have medium densities; gases have low densities because particles are spread far apart. Understanding the particle model helps you explain why solids keep their shape while gases expand to fill a container.
密度反映物质在单位体积内被压缩的紧密程度。公式将质量与体积联系起来。固体通常具有高密度，因为粒子紧密排列；液体密度中等；气体密度很低，因为粒子间距很大。理解粒子模型能帮助你解释为什么固体能保持形状，而气体会扩散至整个容器。
density = mass ÷ volume ρ = m ÷ V
密度 = 质量 ÷ 体积 ρ = m ÷ V
Past paper calculations are straightforward: 'A cube of metal has a mass of 300 g and a volume of 60 cm³. Calculate its density.' Units are very important. If the mass is in grams and volume in cm³, density is in g/cm³; if mass is in kg and volume in m³, density is in kg/m³. Always check the units given in the table. Questions may also ask you to predict whether an object will float or sink based on its density relative to water (1 g/cm³).
真题中的计算很直接：“一块金属的质量为300 g，体积为60 cm³，计算它的密度。” 答案：ρ = 300 g ÷ 60 cm³ = 5 g/cm³。单位至关重要。如果质量用克、体积用立方厘米，密度单位就是克每立方厘米；如果质量用千克、体积用立方米，密度单位就是千克每立方米。一定要看清表格中给出的单位。题目还可能让你根据物体与水的密度大小关系（水为1 g/cm³），预测它是浮起还是沉没。
6. Energy Forms and Transfers | 能量形式与转化
Energy is a unifying theme in Cambridge Physics. Recognise these forms: kinetic (movement), thermal (heat), light, sound, electrical, chemical (stored in food and batteries), and gravitational potential (energy due to height). The law of conservation of energy states that energy can never be created or destroyed, only transferred from one store to another or transformed from one form to another.
能量是剑桥物理中一个贯穿前后的话题。要认识这些形式：动能（运动）、热能、光能、声能、电能、化学能（储存在食物和电池中）以及重力势能（因高度而具有的能量）。能量守恒定律指出，能量既不会凭空产生也不会消失，只能从一个储存库转移到另一个，或从一种形式转化为另一种形式。
In past papers, you will often see flow diagrams or Sankey diagrams for devices such as a torch or a hairdryer. For example, a battery torch has the energy transfer: chemical energy in the battery → electrical energy in the wires → light energy + thermal energy (wasted). Be prepared to identify the useful energy output and the wasted energy, which almost always ends up heating the surroundings. A question may ask: 'What happens to the wasted energy?' The answer is that it is dissipated as thermal energy (heat) and spreads out into the air.
在真题中，你经常会看到手电筒或电吹风等装置的能流图或桑基图。例如，手电筒的能量转化是：电池中的化学能 → 导线中的电能 → 光能 + 热能（浪费）。要能区分有用能量输出和浪费的能量，浪费的能量几乎最终都会转化为周围环境的热。题目可能会问：“浪费的能量到哪里去了？”答案是它以热能（热）的形式散失，并扩散到空气中。
7. Series and Parallel Circuits | 串联与并联电路
Understanding how to build and draw circuits is a hands-on part of the test. In a series circuit, all components are connected one after another in a
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