Year 8 CIE Physics: Core Knowledge Summary | Year 8 CIE 物理：核心知识点梳理

📚 Year 8 CIE Physics: Core Knowledge Summary | Year 8 CIE 物理：核心知识点梳理

Welcome to the ultimate revision guide for Year 8 CIE Physics. This article covers all the key concepts you need to master at this stage, from measurement and forces to electricity, waves, and magnetism. Each section is presented in a clear, bilingual format to help you review and remember the essential facts. Use this as your checkpoint companion, and you will be well-prepared for any assessment.

欢迎来到 Year 8 CIE 物理终极复习指南。本文涵盖了本阶段你需要掌握的所有核心概念，从测量和力，到电学、波和磁学。每个部分都以清晰的双语形式呈现，帮助你复习并记住关键知识。将这篇文章作为你的 checkpoint 备考伴侣，你将为任何评估做好充分准备。

1. Physical Quantities and Measurement | 物理量与测量

Length is measured in metres (m), and common tools include rulers and measuring tapes. For smaller lengths, centimetres (cm) and millimetres (mm) are used; 1 m = 100 cm = 1000 mm.

长度以米 (m) 为单位进行测量，常用工具有直尺和卷尺。对于更小的长度，使用厘米 (cm) 和毫米 (mm)；1 m = 100 cm = 1000 mm。

Mass is measured in kilograms (kg) using a balance, such as a digital balance or a beam balance. Often, grams (g) are also used; 1 kg = 1000 g.

质量以千克 (kg) 为单位，使用天平测量，例如电子天平或杠杆天平。也常用克 (g)；1 kg = 1000 g。

Time is measured in seconds (s) using a stopwatch or timer. For longer intervals, minutes (min) and hours (h) are also common.

时间以秒 (s) 为单位，使用秒表或计时器测量。较长的时间间隔也常用分钟 (min) 和小时 (h)。

The volume of a liquid is measured in litres (L) or millilitres (mL) using a measuring cylinder. When reading the volume, your eye must be level with the bottom of the meniscus to avoid parallax error.

液体的体积以升 (L) 或毫升 (mL) 为单位，使用量筒测量。读数时，视线必须与弯月面的底部保持水平，以避免视差误差。

The volume of a regular solid can be calculated by multiplying length x width x height and is expressed in cubic centimetres (cm³) or cubic metres (m³).

规则固体的体积可以通过长 × 宽 × 高计算，单位用立方厘米 (cm³) 或立方米 (m³) 表示。

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2. Forces and Their Effects | 力及其效果

A force is a push or a pull that can change the shape, speed, or direction of an object. Force is measured in newtons (N).

力是一种推或拉，可以改变物体的形状、速度或方向。力的单位是牛顿 (N)。

Forces can be contact forces (e.g., friction, air resistance) or non‑contact forces (e.g., gravitational force, magnetic force).

力可以是接触力（如摩擦力、空气阻力），也可以是非接触力（如重力、磁力）。

Weight is the force of gravity on an object and is calculated by Weight = mass × gravitational field strength. On Earth, the gravitational field strength g is approximately 10 N/kg.

重量是作用在物体上的重力，计算公式为 重量 = 质量 × 重力场强度。在地球上，重力场强度 g 约为 10 N/kg。

Friction is a force that opposes motion between two surfaces in contact. It can be increased by making surfaces rougher or by pressing them together more firmly.

摩擦力是阻碍两个接触表面相对运动的力。可以通过使表面更粗糙或更紧地挤压来增大摩擦力。

Air resistance is a type of friction that acts on objects moving through air. It increases with speed and with the surface area of the object.

空气阻力是一种摩擦力，作用在空气中运动的物体上。它随速度和物体的表面积增大而增大。

If the resultant force on an object is zero, the object will remain at rest or continue moving at a constant speed in a straight line. This is Newton’s first law of motion.

如果物体受到的合力为零，物体将保持静止或继续沿直线匀速运动。这就是牛顿第一运动定律。

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3. Motion and Speed | 运动与速度

Speed tells us how fast an object is moving. It is the distance travelled per unit time. The formula is:

速度告诉我们物体运动的快慢。它是单位时间内通过的路程。公式为：

average speed = total distance / total time

平均速度 = 总路程 / 总时间

In symbols, we often write v = s / t, where v is speed, s is distance, and t is time. The SI unit of speed is metres per second (m/s), but kilometres per hour (km/h) is also common.

符号上我们常写成 v = s / t，其中 v 是速度，s 是距离，t 是时间。速度的国际单位是米每秒 (m/s)，但千米每小时 (km/h) 也很常用。

On a distance‑time graph, a straight line sloping upwards represents constant speed. A horizontal line means the object is stationary. The steeper the line, the greater the speed.

在距离‑时间图中，一条斜向上的直线表示匀速运动。水平线表示物体静止。线越陡，速度越大。

If the line on a distance‑time graph curves upwards, the speed is increasing – the object is accelerating.

如果距离‑时间图上的线向上弯曲，表示速度在增加——物体在加速。

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4. Energy Types and Conservation | 能量类型与守恒

Energy exists in many forms: kinetic energy (movement), gravitational potential energy (height), elastic potential energy (stretched or compressed), thermal (heat) energy, chemical energy (stored in fuels and food), light energy, sound energy, electrical energy, and nuclear energy.

能量以多种形式存在：动能（运动）、重力势能（高度）、弹性势能（拉伸或压缩）、热能、化学能（储存在燃料和食物中）、光能、声能、电能和核能。

The law of conservation of energy states that energy cannot be created or destroyed. It can only be transferred from one form to another or from one place to another. The total amount of energy always remains constant.

能量守恒定律指出，能量既不能被创造也不能被消灭。它只能从一种形式转化为另一种形式，或从一个地方转移到另一个地方。能量的总量始终保持不变。

In a simple circuit, the battery converts chemical energy into electrical energy, and the lamp converts electrical energy into light and heat. Sankey diagrams are used to show energy transfers visually; the width of each arrow represents the amount of energy.

在一个简单电路中，电池将化学能转化为电能，灯泡将电能转化为光能和热能。桑基图用于直观地显示能量转移；每个箭头的宽度表示能量的多少。

Useful energy is the part that does the desired job; wasted energy usually spreads into the surroundings as heat. Efficiency is the fraction of useful output energy compared to total input energy.

有用能量是做所需功的那部分能量；浪费的能量通常以热的形式散失到周围环境中。效率是有用输出能量与总输入能量的比值。

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5. Heat Transfer | 热传递

Heat always moves from a region of higher temperature to a region of lower temperature. The three methods of heat transfer are conduction, convection, and radiation.

热量总是从温度较高的区域向温度较低的区域传递。热传递的三种方式是传导、对流和辐射。

Conduction occurs mainly in solids when particles vibrate and pass on energy without moving from their positions. Metals are good conductors because they have free electrons that carry heat energy quickly. Non‑metals, such as wood and plastic, are insulators.

传导主要发生在固体中，粒子振动并将能量传递出去而本身并不移动。金属是热的良导体，因为它们有自由电子可以快速携带热能。非金属如木材和塑料是绝缘体。

Convection occurs in liquids and gases. When a fluid is heated, it expands, becomes less dense, and rises. Cooler, denser fluid sinks to take its place, setting up a convection current.

对流发生在液体和气体中。当流体受热时，它会膨胀、密度变小并上升。较冷、密度较大的流体下沉取而代之，形成对流循环。

Radiation is the transfer of heat by infrared waves. It does not need a medium and can travel through a vacuum, which is how the Sun’s heat reaches Earth. Dark, matt surfaces are the best absorbers and emitters of radiation; shiny, light surfaces are poor absorbers and good reflectors.

辐射是通过红外线传递热量。它不需要介质，可以在真空中传播，这就是太阳的热量到达地球的方式。暗色粗糙表面是辐射的最好吸收体和发射体；光亮浅色表面吸收差而反射好。

To reduce heat loss, we use insulation such as double‑glazed windows, fibreglass loft insulation, and cavity wall insulation, which trap air (a good insulator) and minimise convection and conduction.

为了减少热量散失，我们使用隔热材料，如双层玻璃窗、玻璃纤维阁楼隔热材料和空心墙隔热层，它们封存空气（一种良好的绝缘体）并最大限度地减少对流和传导。

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6. Sound Waves | 声波

Sound is produced by vibrations. These vibrations travel through a medium (solid, liquid, or gas) as longitudinal waves. In a longitudinal wave, the particles vibrate parallel to the direction the wave travels.

声音由振动产生。这些振动以纵波的形式通过介质（固体、液体或气体）传播。在纵波中，粒子的振动方向与波的传播方向平行。

Sound cannot travel through a vacuum because there are no particles to carry the vibrations. In air at room temperature, the speed of sound is about 340 m/s. It travels faster in liquids and even faster in solids.

声音不能在真空中传播，因为没有粒子携带振动。在室温下的空气中，声速约为 340 m/s。在液体中传播更快，在固体中更快。

The pitch of a sound depends on its frequency. Frequency is the number of vibrations per second, measured in hertz (Hz). A higher frequency gives a higher pitch.

音调取决于声音的频率。频率是每秒振动的次数，单位是赫兹 (Hz)。频率越高，音调越高。

The loudness of a sound depends on its amplitude. A larger amplitude means the wave carries more energy and the sound is louder.

响度取决于振幅。振幅越大，意味着波携带的能量越多，声音越响。

Humans can hear sounds in the frequency range from about 20 Hz to 20 000 Hz. Sounds above this range are called ultrasound, and those below are infrasound.

人类能听到约 20 Hz 到 20 000 Hz 频率范围内的声音。高于此范围的声音叫超声波，低于此范围的叫次声波。

Echoes are reflections of sound. They occur when sound waves bounce off a hard, smooth surface. Echoes are used in sonar and by bats for navigation.

回声是声音的反射。当声波遇到坚硬光滑的表面反弹时产生回声。回声被用于声呐以及蝙蝠的导航。

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7. Light and Optics | 光与光学

Light travels in straight lines until it hits an object. This explains the formation of shadows, which are regions where light is blocked.

光沿直线传播，直到碰到物体为止。这解释了影子的形成，影子是光被阻挡的区域。

Reflection occurs when light bounces off a surface. The law of reflection states that the angle of incidence equals the angle of reflection. Both angles are measured from the normal, an imaginary line perpendicular to the surface.

反射发生在光从表面反弹时。反射定律指出，入射角等于反射角。这两个角都从法线（一条垂直于表面的假想线）量起。

A plane mirror produces a virtual image that is upright, the same size as the object, and appears to be the same distance behind the mirror as the object is in front. The image is also laterally inverted (left and right are swapped).

平面镜产生一个正立的虚像，与物体大小相同，且在镜后的距离似乎与物体到镜子的距离相等。像也是横向反转的（左右互换）。

Refraction is the bending of light when it passes from one transparent medium to another. This happens because the speed of light changes. When light enters a denser medium (e.g., from air to glass), it slows down and bends towards the normal. When it enters a less dense medium, it speeds up and bends away from the normal.

折射是光从一种透明介质进入另一种透明介质时发生的弯曲。这是因为光速发生了变化。当光进入光密介质时（如从空气到玻璃），速度减慢并靠近法线偏折。当进入光疏介质时，速度加快并远离法线偏折。

White light can be dispersed by a prism into the seven colours of the spectrum: red, orange, yellow, green, blue, indigo, and violet. This happens because each colour has a slightly different speed in glass, so each is refracted by a different amount.

白光可以被棱镜色散成七种颜色的光谱：红、橙、黄、绿、蓝、靛、紫。这是因为每种颜色在玻璃中的速度略有不同，所以每种颜色的折射程度不同。

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8. Electric Circuits | 电路

A basic electric circuit consists of a power source (such as a cell or battery), connecting wires, a switch, and a load (such as a lamp, buzzer, or motor).

一个基本电路由电源（如电池）、导线、开关和用电器（如灯泡、蜂鸣器或电动机）组成。

Electric current is the flow of electric charge. It is measured in amperes (A) using an ammeter connected in series. Current always requires a complete circuit to flow.

电流是电荷的流动。用安培表串联在电路中测量电流，单位是安培 (A)。电流始终需要一个完整的回路才能流动。

Voltage (potential difference) is the ‘push’ that drives charge through a circuit. It is measured in volts (V) using a voltmeter connected in parallel across a component.

电压（电位差）是推动电荷通过电路的’推力’。用伏特表并联在元件两端测量电压，单位是伏特 (V)。

Resistance is the opposition to the flow of current. It is measured in ohms (Ω). Components such as resistors, filament lamps, and thermistors all have resistance. For a fixed resistor, the resistance stays the same if the temperature is constant.

电阻是对电流流动的阻碍。单位是欧姆 (Ω)。电阻器、灯丝灯泡和热敏电阻等元件都有电阻。对于定值电阻，如果温度不变，其电阻保持不变。

The relationship between voltage, current, and resistance is given by Ohm’s law, which can be written as:

电压、电流和电阻之间的关系由欧姆定律给出，可以写为：

V = I × R

V = I × R (电压 = 电流 × 电阻)

Series and parallel circuits have different rules. The table below summarises the key differences:

串联和并联电路有不同的规律。下表总结了主要区别：

Property / 性质	Series Circuit / 串联电路	Parallel Circuit / 并联电路
Current / 电流	Same at all points / 各处电流相等	Sum of branch currents equals supply current / 各支路电流之和等于干路电流
Voltage / 电压	Sum of voltages across components equals supply voltage / 各元件电压之和等于电源电压	Same across each branch / 各支路两端电压相等
Resistance / 电阻	Total resistance increases as more components are added / 增加元件总电阻增大	Total resistance decreases as more branches are added / 增加支路总电阻减小
If one component fails / 一个元件损坏	Whole circuit stops working / 整个电路停止工作	Other branches continue to work / 其他支路继续工作

A short circuit occurs when current finds a path of very low resistance, bypassing the intended load. This can cause overheating and danger, so fuses or circuit breakers are used for protection.

当电流找到一条电阻极低的路径，绕过预定的用电器时，就发生了短路。这可能导致过热和危险，因此使用保险丝或断路器进行保护。

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9. Magnetism and Electromagnetism | 磁与电磁

A magnet has a north pole (N) and a south pole (S). Like poles repel each other; unlike poles attract. Magnetic forces act at a distance without physical contact.

磁铁有一个北极 (N) 和一个南极 (S)。同极相斥，异极相吸。磁力可以不接触地隔空作用。

Magnetic materials are those that can be attracted by a magnet, mainly iron, nickel, and cobalt. Steel is an alloy of iron that can be permanently magnetised.

磁性材料是能被磁铁吸引的材料，主要有铁、镍和钴。钢是铁的一种合金，可以被永久磁化。

The magnetic field is the region around a magnet where magnetic forces are felt. Field lines show the direction (from N to S) and strength of the field. The closer the lines, the stronger the field.

磁场是磁铁周围能感受到磁力的区域。磁感线表示磁场的方向（从 N 到 S）和强弱。线越密集，磁场越强。

The Earth itself behaves like a giant bar magnet. Its magnetic north pole is near the geographic South Pole, which is why a compass needle’s north‑seeking pole points towards the geographic north.

地球本身就像一个巨大的条形磁铁。它的磁北极靠近地理南极，这就是指南针的指北极指向地理北方的原因。

An electromagnet is made by wrapping a wire coil around a soft iron core and passing an electric current through the coil. The magnetic field can be strengthened by increasing the current, adding more turns of wire, or using an iron core.

电磁铁是通过在软铁芯上缠绕线圈并在线圈中通入电流制成的。通过增大电流、增加线圈匝数或使用铁芯，可以增强其磁场。

Electromagnets have the advantage that their magnetism can be switched on and off and their strength easily controlled. They are used in lifting scrap metal, electric bells, relays, and loudspeakers.

电磁铁的优点是磁性可以通断，且强弱易于控制。它们用于起重废铁、电铃、继电器和扬声器中。

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10. Matter and Density | 物质与密度

Matter can exist in three states

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