📚 Year 7 OCR Physics: High-Frequency Topics and Common Mistake Analysis | Year 7 OCR 物理：高频考点与易错题分析
Year 7 OCR Physics lays the essential groundwork for understanding the physical world, from forces and energy to electricity and waves. However, students often stumble on specific concepts that constantly reappear in exams. This article zooms in on the highest-frequency topics and the most common mistakes, giving you clear explanations and exam-ready tips.
Year 7 OCR 物理为认识物理世界打下重要基础，涵盖力、能量、电和波等内容。然而，学生在一些反复出现在考试中的概念上经常出错。本文聚焦最高频的考点与最常见的错误，给出清晰的解释和应考技巧。
1. Forces: Contact vs. Non-Contact | 力：接触力与非接触力
Forces are pushes or pulls. They can be grouped as contact forces, which require touching (friction, tension, air resistance, normal reaction), or non-contact forces, which act over a distance (gravity, magnetism, electrostatic force).
力是推或拉的作用。力可分为需要接触的接触力（摩擦力、张力、空气阻力、法向反作用力）和隔空作用的非接触力（重力、磁力、静电力）。
A very frequent exam mistake is classifying air resistance as non-contact because you cannot see air. In reality, air resistance arises from collisions with air particles, so it is a contact force. Similarly, students sometimes forget that upthrust in water is a contact force.
考试中一个极常见的错误是把空气阻力归为非接触力，因为空气看不见。实际上，空气阻力来自与空气粒子的碰撞，因此它是接触力。同样，学生有时会忘记水中的浮力也是接触力。
To decide quickly, ask: does the object have to be in physical contact with a substance (solid, liquid, or gas)? If yes, it is a contact force. If the force can still act in a vacuum, it is non-contact.
要快速判断，可以问：物体是否需要与物质（固体、液体或气体）直接接触？如果需要，就是接触力。如果该力在真空中仍能作用，那就是非接触力。
| Contact Forces | Non-contact Forces |
|---|---|
| Friction | Gravity (weight) |
| Air resistance (drag) | Magnetic force |
| Tension in a rope | Electrostatic force |
| Normal reaction |
Use this table to test yourself: cover the right column and try to recall two non-contact forces – gravity and magnetism are the most common answers expected in Year 7.
用上表自测：遮住右列，试着说出两种非接触力——重力和磁力是 Year 7 最常考到的答案。
2. Mass vs. Weight: Don't Mix Them Up | 质量与重量：别再混淆了
Mass is the amount of matter in an object; it does not change wherever you go. It is measured in kilograms (kg) using a balance. Weight is the force of gravity pulling on that mass, measured in newtons (N) with a spring scale or force meter.
质量是物体所含物质的多少，无论去到哪里都不变，用天平测量，单位是千克(kg)。重量是重力拉物体的力，用弹簧秤或测力计测量，单位是牛顿(N)。
One of the most stubborn mistakes is saying 'my weight is 50 kg' eld strength g ≈ 10 N/kg, so a 50 kg student weighs about 500 N. The correct expression is 'my mass is 50 kg'.
最顽固的错误就是说“我的重量是 50 公斤”。那是你的质量。在地球上，引力场强度 g ≈ 10 N/kg，所以 50 kg 的学生重约 500 N。正确的表述是“我的质量是 50 kg”。
Weight changes with location: on the Moon your mass is still 50 kg but your weight is only about 83 N because the Moon's gravity is weaker. In exam questions, if you see an object on the Moon, remember its mass stays constant but its weight decreases.
重量会随地点改变：在月球上你的质量仍是 50 kg，但重量只有约 83 N，因为月球引力更弱。考试中看到月球上的物体，要记住质量不变但重量变小。
l field strength. Many questions ask you to calculate one given the other two, so memorise W = m g and always write the unit N for weight.
记住关系式很简单：重量 = 质量 × 引力场强度。很多题目要求已知两个量计算第三个，因此牢记 W = m g，并且重量始终带单位 N。
3. Energy Stores, Transfers, and Conservation | 能量储存、转移与守恒
The law of conservation of energy states that energy cannot be created or destroyed, only transferred between stores. In Year 7 you need to know these main stores: kinetic, gravitational potential, elastic potential, thermal (internal), chemical, and nuclear.
能量守恒定律指出，能量不能创生也不能消灭，只能在储存间转移。
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