📚 Key Topics in Year 8 WJEC Physics | Year 8 WJEC 物理核心知识点梳理
Welcome to your comprehensive revision guide for Year 8 WJEC Physics. This article summarises the essential concepts you need to master, from forces and energy to electricity and space. Each topic is broken down into clear explanations with key equations, examples, and scientific vocabulary. Use this resource alongside your class notes to build a solid foundation for GCSE Physics.
欢迎阅读 Year 8 WJEC 物理综合复习指南。本文梳理了你需要掌握的核心概念，涵盖力、能量、电学到太空等领域。每个主题都以清晰的解释、关键公式和科学术语进行分解，并配以实例。请将本文与课堂笔记结合使用，为 GCSE 物理打下坚实基础。
1. Forces and Motion | 力与运动
A force is a push or a pull that can change an object's speed, direction, or shape. Forces are measured in newtons (N). There are two main types: contact forces (e.g. friction, air resistance) and non-contact forces (e.g. gravity, magnetic force). When multiple forces act on an object, we consider the resultant force. If forces are balanced, the object stays at rest or continues at a constant velocity. Unbalanced forces cause acceleration or deceleration.
力是一种推或拉的作用，可以改变物体的速度、方向或形状。力的单位是牛顿（N）。力分为两大类：接触力（如摩擦力、空气阻力）和非接触力（如重力、磁力）。当多个力作用于物体时，我们需要考虑合力。如果作用力互相平衡，物体将保持静止或匀速直线运动；若不平衡，物体就会加速或减速。
Motion can be described using speed calculations. Average speed is the distance travelled divided by the time taken. You should be able to use the formula and interpret distance–time graphs. A straight sloping line indicates constant speed, while a horizontal line means the object is stationary.
我们可以通过速度计算来描述运动。平均速度等于移动的距离除以所用时间。你需要熟练使用这一公式，并能够解读距离–时间图像。一条倾斜的直线表示匀速运动，水平线则表示物体静止。
average speed = total distance ÷ total time
平均速度 = 总距离 ÷ 总时间。使用此公式时要注意单位一致，例如距离用米（m），时间用秒（s），速度单位就是 m/s。
- distance: metre (m)
- time: second (s)
- speed: metre per second (m/s)
主要单位：距离–米（m），时间–秒（s），速度–米每秒（m/s）。
2. Energy Transfers and Stores | 能量转移与储存
Energy is the ability to do work. It can be stored in various ways: kinetic (moving), gravitational potential (height), elastic potential (stretched or compressed springs), thermal (heat), chemical (food, fuel), and nuclear. Energy is measured in joules (J). The principle of conservation of energy states that energy cannot be created or destroyed, only transferred between stores or transformed from one form to another.
能量是做功的能力。能量可以以多种方式储存：动能（运动）、重力势能（高度）、弹性势能（被拉伸或压缩的弹簧）、热能、化学能（食物、燃料）以及核能。能量的单位是焦耳（J）。能量守恒原理指出，能量不会凭空产生或消失，只会在不同储存之间转移或者从一种形式转化为另一种形式。
bject, you increase its gravitational potential energy (GPE). GPE = mass × gravitational field strength × height. On Earth, the gravitational field strength is about 10 N/kg.
当一个力推动物体移动时，我们就说做了功。功的大小等于力乘以在力的方向上移动的距离。如果你将一个物体举高，就会增加其重力势能。重力势能 = 质量 × 重力场强度 × 高度。在地球表面，重力场强度约为 10 N/kg。
work done = force × distance
功 = 力 × 距离
GPE = m × g × h
重力势能 = 质量 × 10 × 高度（单位：焦耳 J）
Power is the rate of energy transfer. One watt is one joule per second. You may calculate power by dividing energy transferred by time taken.
功率是能量转移的速率。1 瓦特等于每秒 1 焦耳。你可以用转移的能量除以时间来计算功率。
power = energy transferred ÷ time
功率 = 转移的能量 ÷ 时间
3. Electricity and Circuits | 电与电路
An electric circuit requires a complete loop of conducting material through which current can flow. Circuit diagrams use standard symbols: cell, battery, switch, lamp, resistor, variable resistor, ammeter, voltmeter, fuse, and diode. Current (I) is the flow of electric charge and is measured in amperes (A) using an ammeter connected in series. Voltage (V) is the 'push' that drives the current and is measured in volts (V) using a voltmeter connected in parallel.
电路需要完整的导电回路，电流才能流通。电路图使用标准符号：电池、电池组、开关、灯泡、电阻、可变电阻、电流表、电压表、熔断器和二极管。电流（I）是电荷的流动，单位为安培（A），使用串联的电流表测量。电压（V）是驱动电流的“推力”，单位为伏特（V），使用并联的电压表测量。
Resistance (R) tells us how difficult it is for current to pass through a component. It is measured in ohms (Ω). In a series circuit, the current is the same everywhere, but the voltage is shared across components. In a parallel circuit, the voltage across each branch is the same, but the current splits.
电阻（R）表示电流通过元件的难易程度，单位是欧姆（Ω）。在串联电路中，各处电流相等，但电压在元件间分配。在并联电路中，各支路电压相等，但电流会分流。
resistance = voltage ÷ current
电阻 = 电压 ÷ 电流（欧姆定律）
Safety around electricity is vital. Never touch exposed wires; use insulated tools and avoid water near electrical appliances. Fuses and circuit breakers protect against excessive current.
用电安全至关重要。切勿触摸裸露的电线；应使用绝缘工具并让电器远离水。熔断器和断路器可以在电流过大时提供保护。
4. Magnetism and Electromagnets | 磁与电磁铁
Magnets have north and south poles. Like poles repel and unlike poles attract. Magnetic field lines show the direction of the magnetic force: they run from north to south outside the magnet. An electromagnet is a coil of wire (solenoid) with an iron core. When current flows, a strong magnetic field is produced. Electromagnets can be made stronger by increasing the number of coils, increasing the current, or using a soft iron core.
磁铁有北极和南极。同性磁极互相排斥，异性磁极互相吸引。磁感线显示磁力的方向，在磁铁外部从北极指向南极。电磁铁是由线圈（螺线管）和铁芯组成的。当电流通过时，就会产生强磁场。增加线圈匝数、增大电流或使用软铁芯都可以增强电磁铁。
Electromagnets are used in many devices, such as electric bells, relays, and for lifting scrap metal in scrapyards. Unlike permanent magnets, their magnetism can be switched on and off.
电磁铁在很多设备中都有应用，例如电铃、继电器，以及废料场里用来吸起废金属的电磁起重机。与永磁体不同，电磁铁的磁性可以随时接通和断开。
5. Waves: Sound and Light | 波：声与光
Waves transfer energy without transferring matter. In transverse waves, vibrations are perpendicular to the direction of energy travel (e.g. light, water waves). In longitudinal waves, vibrations are parallel to the direction of energy travel (e.g. sound). Sound needs a medium (solid, liquid or gas) to travel; it cannot travel through a vacuum. The speed of sound in air is about 340 m/s. Echoes are reflections of sound.
波传递能量而不传递物质。在横波中，振动方向与能量传播方向垂直（例如光、水波）。在纵波中，振动方向与能量传播方向平行（例如声音）。声音的传播需要介质（固体、液体或气体），无法在真空中传播。声音在空气中的速度约为 340 m/s。回声就是声音的
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