📚 Year 8 AQA Physics: Key Knowledge Review | Year 8 AQA 物理：核心知识点梳理
This article summarises the core knowledge for Year 8 AQA Physics, covering energy, electricity, forces, magnetism, and waves. Understanding these fundamentals will help you build a strong foundation for GCSE and beyond.
本文梳理了 Year 8 AQA 物理的核心知识点，涵盖能量、电学、力、磁学和波等内容。掌握这些基础知识将为 GCSE 阶段打下坚实基础，并有助于理解更高级的物理概念。
1. Energy Stores and Transfers | 能量储存与转移
Energy is stored in different forms, such as kinetic, thermal, chemical, and gravitational potential. It can be transferred between stores through heating, work done by forces, or waves. Energy is always conserved: it cannot be created or destroyed, only moved from one store to another.
能量以不同形式储存，例如动能、热能、化学能和重力势能。能量可以通过加热、力做功或波的方式在不同储存间转移。能量总是守恒的：它不能被创造或消灭，只能从一个储存转移到另一个储存。
The main energy stores and examples are shown below:
| Energy Store | Example |
|---|---|
| Kinetic | A moving bicycle |
| Thermal | A hot cup of tea |
| Chemical | Food, battery |
| Gravitational potential | A book on a high shelf |
| Elastic potential | A stretched rubber band |
| Nuclear | Uranium in a power station |
主要的能量储存及其例子如上表所示：动能、热能、化学能、重力势能、弹性势能和核能。转移途径包括机械做功（力移动物体）、加热（温度差）和辐射（如光、声波）。理解这些储存和转移方式对分析能量变化至关重要。
2. Heating and Temperature | 热与温度
Temperature is a measure of the average kinetic energy of particles; it tells us how hot or cold an object is. Heat, on the other hand, is the transfer of thermal energy from a hotter region to a cooler one. Three main processes transfer heat: conduction, convection, and radiation.
温度是粒子平均动能的量度，表明物体的冷热程度。热量则是热能从较热区域向较冷区域的转移。传递热量的三种主要方式是：传导、对流和辐射。
- Conduction occurs mainly in solids when vibrating particles pass energy to neighbouring particles. Metals are good conductors; non-metals and gases are insulators.
传导主要发生在固体中，粒子振动将能量传递给相邻粒子。金属是良导体，非金属和气体是绝缘体。 - Convection happens in fluids (liquids and gases). Warmer, less dense fluid rises, and cooler, denser fluid sinks, setting up a convection current.
对流发生在流体（液体和气体）中。较热、密度较小的流体上升，较冷、密度较大的流体下沉，形成对流循环。 - Radiation transfers energy by infrared waves that can travel through a vacuum. All objects emit thermal radiation; hotter objects emit more.
辐射通过红外波传递能量，可在真空中传播。所有物体都发出热辐射，温度越高辐射越强。
3. Electricity and Simple Circuits | 电与简单电路
An electric circuit must be complete (a closed loop) and contain a power source for current to flow. Circuit diagrams use standard symbols to represent components. Common symbols include: cell, battery, switch, lamp, buzzer, resistor, and variable resistor.
电路必须是完整的闭合回路并有电源才能让电流流动。电路图使用标准符号来表示元件。常见符号有：电池、开关、灯泡、蜂鸣器、电阻和可变电阻等。
In a series circuit, components are connected end-to-end, so the current is the same everywhere. If one component fails, the circuit breaks. In a parallel circuit, components are connected on separate branches; the total current splits between branches, and each branch receives the full voltage of the supply. Parallel circuits allow other components to keep working if one branch breaks.
在串联电路中，元件首尾相连，因此各处电流相同。如果一个元件损坏，整个电路断开。在并联电路中，元件连接在不同的支路上；总电流在各支路间分配，每个支路获得电源的全部电压。并联电路即使一条支路断开，其他元件仍能工作。
4. Current, Voltage, and Resistance | 电流、电压与电阻
Electric current (I) is the flow of electric charge, measured in amperes (A). In a metal wire, current is a flow of electrons. Voltage, or potential difference (V), measures the energy transferred per unit of charge, in volts (V). Resistance (R) is a measure of how difficult it is for current to flow, measured in ohms (Ω).
电流 (I) 是电荷的流动，单位为安培 (A)。在金属导线中，电流是电子的流动。电压或电势差 (V) 衡量每单位电荷转移的能量，单位为伏特 (V)。电阻 (R) 衡量电流流动的难易程度，单位为欧姆 (Ω)。
Ohm’s law relates these quantities:
V = I × R
欧姆定律将它们联系起来：电压 = 电流 × 电阻。电阻器会阻碍电流，而导线的电阻通常很小。增加电压会驱动更大的电流，而增加电阻会减小电流。
In a series circuit, total resistance is the sum of individual resistances. Current is the same at all points, and the supply voltage is shared across components. In a parallel circuit, the total resistance is lower than the smallest individual branch resistance. The potential difference across each branch is the same as the supply voltage.
在串联电路中，总电阻等于各电阻之和。各处电流相等，电源电压被元件分担。在并联电路中，总电阻小于最小的支路电阻，各支路两端的电压与电源电压相等。
5. 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). When forces on an object are balanced, the object remains at rest or continues moving at constant speed in a straight line. If forces are unbalanced, the object accelerates in the direction of the resultant force.
力是推或拉，可以改变物体的速度、方向或形状。力的单位是牛顿 (N)。当作用在物体上的力平衡时，物体会保持静止或沿直线匀速运动。如果力不平衡，物体就会在合力的方向上加速。
Contact forces need physical contact, e.g., friction, air resistance, and tension. Non-contact forces act over a distance, e.g., gravitational force, magnetic force, and electrostatic force. Weight is the force of gravity on a mass: W = m × g, where g ≈ 10 m/s² on Earth.
接触力需要物体相互接触，例如摩擦力、空气阻力和张力。非接触力可以在一定距离外作用，例如重力、磁力和静电力。重量是质量所受的重力：重量 = 质量 × 重力场强度，地球上 g ≈ 10 m/s²。
6. Speed and Motion | 速度与运动
Speed is how fast an object moves, calculated as distance divided by time. The average speed of an object can be found using:
speed = distance ÷ time
速度描述物体运动的快慢，等于距离除以时间。平均速度可用公式：速度 = 距离 ÷ 时间 计算。
Velocity is speed in a given direction. Acceleration is the rate of change of velocity. An object accelerates if its speed changes or if it changes direction. On a distance–time graph, a straight horizontal line indicates the object is stationary; a straight sloping line shows constant speed; a curved line shows acceleration. A steeper gradient means a higher speed.
速度是带有方向的速率。加速度是速度变化的快慢。物体改变速度大小或改变方向时都在加速。在距离-时间图中，水平直线表示物体静止；斜直线表示匀速运动；曲线表示加速。斜率越大，速度越高。
7. Magnetism | 磁学
Magnets have two poles: north (N) and south (S). Like poles repel; unlike poles attract. Permanent magnets are made from magnetic materials such as iron, nickel, and cobalt. A magnetic field is the region around a magnet where magnetic forces can be detected. Field lines show the direction a north pole would move: they point from north to south outside the magnet.
磁铁有两极：北极 (N) 和南极 (S)。同极相斥，异极相吸。永磁体由铁、镍、钴等磁性材料制成。磁场是磁体周围能够探测到磁力的区域。磁力线显示北极会移动的方向：在磁体外部，它们从北极指向南极。
The Earth itself has a magnetic field, which is why a compass needle (a small bar magnet) aligns north–south. Magnetic materials can be magnetised by stroking them with a permanent magnet or by placing them in a strong magnetic field. Soft magnetic materials (e.g., iron) easily lose their magnetism; hard magnetic materials (e.g., steel) retain it.
地球本身拥有磁场，这就是指南针（小磁针）指向南北的原因。磁性材料可以通过用永磁体摩擦或置于强磁场中被磁化。软磁材料（如铁）容易失去磁性；硬磁材料（如钢）能保持磁性。
8. Electromagnets | 电磁铁
An electromagnet is a temporary magnet created by passing an electric current through a coil of wire (solenoid) wrapped around an iron core. The magnetic field is present only when the current flows. Its strength can be increased by:
- increasing the number of coil turns;
增加线圈匝数； - increasing the current;
增大电流； - using a soft iron core instead of an air core.
使用软铁芯而非空气芯。
电磁铁是一种暂时磁体，通过让电流流过缠绕在铁芯上的线圈（螺线管）而产生。只有通电时才存在磁场。它广泛应用于继电器、电铃、扬声器和废铁起重机上。电磁铁其优势在于磁力可控，可以通过通断电或改变电流强度来调节。
Electromagnets are used in relays, electric bells, loudspeakers, and lifting scrap metal. Their main advantage is that the magnetism can be switched on and off and varied by changing the current.
9. Sound Waves | 声波
Sound is a longitudinal wave produced by vibrating objects. The vibrations cause compressions and rarefactions in the medium (solid, liquid, or gas). Sound cannot travel through a vacuum. The speed of sound varies: fastest in solids, slower in liquids, and slowest in gases. In air at room temperature, it is about 340 m/s.
声音是由振动产生的纵波。振动在介质（固体、液体或气体）中形成疏密相间的区域。声音不能在真空中传播。声速各不相同：固体中最快，液体中较慢，气体中最慢。室温下空气中的声速约为 340 m/s。
The pitch of a sound depends on its frequency (number of waves per second, measured in hertz, Hz). High frequency gives a high pitch. Loudness depends on the amplitude of the wave: a larger amplitude means a louder sound. Sound waves can be reflected as echoes, and they can be absorbed or transmitted by different materials.
音调取决于频率（每秒波数，单位赫兹 Hz）。频率高则音调高。响度取决于波的振幅：振幅越大，声音越响亮。声波可以反射形成回声，并会被不同材料吸收或透射。
10. Light and Reflection | 光与反射
Light travels in straight lines at a speed of 300,000,000 m/s in a vacuum. When light hits a surface, it can be reflected, absorbed, or transmitted. The law of reflection states: angle of incidence = angle of reflection. These angles are measured from the normal, an imaginary line perpendicular to the surface.
光在真空中沿直线传播，速度为 3 × 10⁸ m/s。当光照射到表面时，可被反射、吸收或透射。反射定律指出：入射角等于反射角。这些角度是从法线（垂直于表面的假想线）开始测量的。
A plane mirror produces a virtual image that is upright, laterally inverted, and the same size as the object. The image appears to be the same distance behind the mirror as the object is in front. Refraction occurs when light passes from one transparent medium to another (e.g., air to glass), causing it to change speed and direction. This makes objects look bent, like a straw in water.
平面镜产生虚像，正立、左右颠倒且与物体等大。像在镜后的距离看起来与物到镜面的距离相等。当光从一种透明介质进入另一种介质（例如空气到玻璃）时会折射，速度与方向发生改变。这使得物体看起来弯曲，如水中的吸管。
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