📚 Year 8 CAIE Physics Core Knowledge Review | Year 8 CAIE 物理核心知识点梳理
This guide covers all the essential topics in Year 8 CAIE Physics, helping students consolidate key concepts and prepare for assessments. From forces and motion to waves and electricity, each section breaks down the syllabus into clear, bite-size points.
本指南涵盖八年级 CAIE 物理所有核心主题，帮助学生巩固关键概念并为评估做好准备。从力与运动到波与电学，每个部分都将课程大纲分解为清晰、易消化的要点。
1. Forces: Types and Effects | 力：类型与作用
A force is a push or pull acting upon an object; it can change the object’s speed, direction, or shape.
力是作用在物体上的推或拉；它可以改变物体的速度、方向或形状。
Contact forces include friction, air resistance, tension, and normal contact force. Non-contact forces are gravity, magnetism, and electrostatic force.
接触力包括摩擦力、空气阻力、拉力和法向接触力。非接触力有重力、磁力和静电力。
Forces are measured in newtons (N) using a force meter or spring balance.
力用牛顿（N）为单位，使用测力计或弹簧秤测量。
A force can be represented by an arrow; the length shows the magnitude, and the arrowhead shows the direction.
力可以用箭头表示；长度表示大小，箭头表示方向。
| English | 中文 |
|---|---|
| Gravity pulls objects towards Earth’s centre | 重力将物体拉向地心 |
| Friction opposes motion between surfaces | 摩擦力阻碍表面之间的运动 |
| Air resistance slows objects moving through air | 空气阻力减慢在空气中运动的物体 |
| Magnetic force acts between magnets | 磁力作用在磁铁之间 |
2. Speed and Motion Graphs | 速度与运动图像
The average speed of an object is found by dividing the total distance travelled by the time taken.
物体的平均速度用通过的总距离除以所用时间来计算。
average speed = total distance ÷ total time
This relationship is often written as v = d / t, where v is speed, d is distance, and t is time.
这个关系常写作 v = d / t，其中 v 表示速度，d 表示距离，t 表示时间。
A distance–time graph shows how far an object has moved over time. A straight, sloping line indicates constant speed, while a horizontal line means the object is stationary.
距离–时间图像显示物体随时间移动的距离。一条倾斜的直线表示匀速运动，而水平线表示物体静止。
The steeper the slope, the greater the speed. If the slope curves upward, the object is accelerating.
斜率越陡，速度越大。如果斜率向上弯曲，说明物体在加速。
Motion can also be described using words such as stationary, constant speed, accelerating, or decelerating.
运动还可以用静止、匀速、加速或减速等词语来描述。
3. Energy: Forms and Conservation | 能量：形式与守恒
Energy is the ability to do work and is measured in joules (J). It exists in many forms, including kinetic, gravitational potential, thermal, chemical, and electrical energy.
能量是做功的能力，以焦耳（J）为单位。能量有多种形式，包括动能、重力势能、热能、化学能和电能。
Kinetic energy is the energy of a moving object and depends on its mass and speed: Eₖ = ½ m v².
动能是运动物体的能量，取决于其质量和速度：Eₖ = ½ m v²。
Eₖ = ½ m v²
Gravitational potential energy (GPE) is stored in objects raised above the ground: Eₚ = m g h, where g is the gravitational field strength (about 10 N/kg on Earth).
重力势能（GPE）储存在被举离地面的物体中：Eₚ = m g h，其中 g 是引力场强度（地球上约为 10 N/kg）。
Eₚ = m g h
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed from one form to another.
能量守恒定律指出，能量既不能创生也不能消灭，只能从一种形式转移或转化为另一种形式。
In any energy transfer, some energy is always dissipated as heat, which spreads out into the surroundings.
在任何能量转移中，总有一部分能量以热的形式耗散到周围环境中。
4. Thermal Physics: Heat Transfer | 热物理：热传递
Heat can be transferred in three ways: conduction, convection, and radiation.
热传递有三种方式：传导、对流和辐射。
Conduction occurs mainly in solids, where vibrating particles pass energy from the hot end to the cold end without the material moving.
传导主要发生在固体中，振动粒子将能量从热端传递到冷端，而材料本身不移动。
Metals are good conductors because they have free electrons that help transfer thermal energy quickly. Non‑metals and gases are usually insulators.
金属是良导体，因为它们有自由电子帮助快速传递热能。非金属和气体通常是绝缘体。
Convection happens in liquids and gases. When a fluid is heated, it expands, becomes less dense, and rises, while cooler, denser fluid sinks – setting up a convection current.
对流发生在液体和气体中。流体受热膨胀、密度减小而上升，较冷、密度较大的流体下沉，从而形成对流循环。
Thermal radiation is the transfer of heat by infrared waves, which can travel through a vacuum and do not need particles.
热辐射是通过红外波传递热量，它可以在真空中传播，不需要介质粒子。
Dark, matt surfaces are good absorbers and emitters of radiation, while shiny, light surfaces reflect it well.
暗色、粗糙的表面是辐射的良好吸收体和发射体，而光亮、浅色的表面能很好地反射辐射。
5. Light: Reflection and Refraction | 光：反射与折射
Light travels in straight lines in a uniform medium. We represent its path using rays with arrows.
光在均匀介质中沿直线传播。我们用带箭头的射线来表示它的路径。
When light bounces off a smooth surface, the angle of incidence (i) equals the angle of reflection (r), measured from the normal – an imaginary line perpendicular to the surface.
当光从光滑表面反射时，入射角（i）等于反射角（r），都是从法线（垂直于表面的假想线）量起。
i = r
Reflection can be regular (from a mirror) or diffuse (from a rough surface), which scatters light in many directions.
反射可以是镜面反射（来自镜子）或漫反射（来自粗糙表面），漫反射将光线散射到各个方向。
Refraction occurs when light passes from one transparent material to another and changes speed, causing it to bend. If it enters a denser medium, it slows down and bends towards the normal.
折射发生在光从一种透明材料进入另一种时，速度改变导致光线弯曲。如果进入光密介质，光速减慢并向法线偏折。
White light can be split into a spectrum of colours (red, orange, yellow, green, blue, indigo, violet) by a prism, a process called dispersion.
白光可以通过棱镜分解成彩色光谱（红、橙、黄、绿、蓝、靛、紫），这个过程称作色散。
6. Sound: Production and Properties | 声音：产生与性质
Sound is produced by vibrations. These vibrations cause particles in a medium (solid, liquid, or gas) to compress and expand, creating a longitudinal wave.
声音由振动产生。这些振动使介质（固体、液体或气体）中的粒子压缩和膨胀，形成纵波。
Sound cannot travel through a vacuum because there are no particles to carry the vibration.
声音不能在真空中传播，因为没有粒子传递振动。
The frequency of a sound wave, measured in hertz (Hz), determines its pitch – higher frequency means a higher pitched sound.
声波的频率以赫兹（Hz）为单位，决定音调的高低——频率越高，音调越高。
The amplitude of the wave determines the loudness or volume: larger amplitude produces a louder sound.
波的振幅决定响度或音量：振幅越大，声音越响。
Humans can typically hear frequencies between 20 Hz and 20 000 Hz. Sounds above this range are called ultrasound.
人类通常能听到 20 Hz 到 20 000 Hz 之间的频率。高于此范围的声音称为超声波。
Sound travels at different speeds in different media – fastest in solids, slower in liquids, and slowest in gases.
声音在不同介质中的传播速度不同——在固体中最快，液体中较慢，气体中最慢。
7. Electric Circuits: Current, Voltage and Resistance | 电路：电流、电压与电阻
An electric circuit is a complete loop that allows electric current to flow from the positive terminal to the negative terminal of a power supply.
电路是一个完整的回路，允许电流从电源的正极流向负极。
Current (I) is the rate of flow of electric charge, measured in amperes (A). Voltage (V), also called potential difference, is the energy transferred per unit charge and is measured in volts (V).
电流（I）是电荷流动的速率，以安培（A）为单位。电压（V），也称电势差，是单位电荷转移的能量，以伏特（V）为单位。
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, and the current splits between branches.
在串联电路中，各处电流相等，但电压分配给各元件。在并联电路中，各支路两端电压相等，电流则分流。
Resistance (R) is a measure of how difficult it is for current to flow. It is measured in ohms (Ω). The relationship between voltage, current and resistance is given by Ohm’s law:
电阻（R）衡量电流流动的难易程度，以欧姆（Ω）为单位。电压、电流和电阻之间的关系由欧姆定律给出：
V = I × R
A resistor or a long, thin wire adds resistance to a circuit, reducing the current.
电阻器或细长的导线会增加电路中的电阻，从而减小电流。
8. Magnetism: Magnets and Fields | 磁学：磁铁与磁场
A magnet has two poles – north (N) and south (S). Like poles repel, and unlike poles attract.
磁铁有两个磁极——北极（N）和南极（S）。同名磁极相互排斥，异名磁极相互吸引。
The region around a magnet where it exerts a force is called a magnetic field. Field lines run from the north pole to the south pole outside the magnet.
磁铁周围施加力的区域称为磁场。磁感线在磁铁外部从北极指向南极。
The Earth itself behaves like a giant magnet with a magnetic north pole (near the geographic South Pole) and a magnetic south pole. A compass needle aligns with this field.
地球本身就像一个巨大的磁铁，拥有磁北极（靠近地理南极）和磁南极。指南针的指针会与这个地磁场对齐。
Only magnetic materials such as iron, nickel and cobalt are attracted to magnets. Steel is an alloy that can be permanently magnetised.
只有铁、镍、钴等磁性材料会被磁铁吸引。钢是一种可以被永久磁化的合金。
A magnetic field can be made visible by sprinkling iron filings around a magnet; they line up along the field lines.
在磁铁周围撒上铁屑可以显示磁场；铁屑会沿着磁感线排列。
9. Electromagnetism | 电磁学
An electromagnet is made by passing an electric current through a coil of wire wound around an iron core. It acts as a magnet only when current flows.
电磁铁是通过让电流流过缠绕在铁芯上的线圈制成的。它只在有电流通过时才具有磁性。
The strength of an electromagnet can be increased by: increasing the current, adding more turns to the coil, or using a soft iron core.
增强电磁铁磁性的方法有：增大电流、增加线圈匝数或使用软铁芯。
Electromagnets are used in many devices, such as electric bells, relays, lifting magnets, and speakers.
电磁铁用于许多设备，如电铃、继电器、起重磁铁和扬声器。
A current-carrying wire creates a circular magnetic field around it. If the wire is coiled into a solenoid, the magnetic field inside becomes strong and uniform.
载流导线会在其周围产生环形磁场。如果将导线绕成螺线管，内部的磁场会变得强而均匀。
The direction of the magnetic field around a wire or a solenoid can be determined using the right-hand grip rule.
导线或螺线管周围的磁场方向可以用右手螺旋定则确定。
10. States of Matter and Density | 物质状态与密度
Matter exists in three main states: solid, liquid, and gas. The particle model
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