📚 Year 8 CAIE Physics: Formula & Theorem Quick Reference Handbook | 八年级 CAIE 物理：公式定理速查手册
This quick reference handbook consolidates essential formulas and key principles from the Year 8 CAIE Physics syllabus. It is designed to help students memorise and apply core relationships for Checkpoint assessments.
本速查手册汇总了八年级 CAIE 物理课程中的基础公式与核心定理，旨在帮助学生记忆并运用关键关系，应对 Checkpoint 测评。
1. Speed and Acceleration | 速度与加速度
Speed is the distance travelled per unit of time. Average speed accounts for the total journey, and acceleration describes how quickly velocity changes.
速度是单位时间内通过的路程。平均速度考虑全程，加速度则描述速度变化的快慢。
speed = distance ÷ time v = s ÷ t
Instantaneous speed can be read from a distance-time graph's gradient. A steeper slope indicates higher speed.
瞬时速度可由距离-时间图的斜率读取。斜率越陡，速度越快。
average speed = total distance ÷ total time
For objects moving with non-uniform motion, average speed smooths out variations over the whole trip.
对于非匀速运动的物体，平均速度平滑了全程的速度变化。
celeration = (final velocity − initial velocity) ÷ time taken a = (v − u) ÷ t
Acceleration is measured in m/s². A positive value means speeding up; a negative value indicates deceleration.
加速度的单位是米每二次方秒（m/s²）。正值表示加速，负值表示减速。
2. Forces and Newton’s Laws | 力与牛顿定律
Newton’s First Law states that an object remains at rest or in uniform motion unless acted upon by a resultant force.
牛顿第一定律指出，除非受到合外力作用，物体将保持静止或匀速直线运动状态。
Resultant force = mass × acceleration F = m a
Newton’s Second Law quantifies how net force causes acceleration. A larger mass resists changes in motion more strongly.
牛顿第二定律量化了合外力如何产生加速度。质量越大，抵抗运动状态改变的能力越强。
Newton’s Third Law reminds us that forces come in pairs: if object A exerts a force on B, B exerts an equal and opposite force on A.
牛顿第三定律提醒我们力成对出现：若物体 A 对 B 施加力，则 B 同时对 A 施加大小相等、方向相反的力。
weight = mass × gravitational field strength W = m g
On Earth, g is about 10 N/kg (or 9.8 N/kg). Weight is a force measured in newtons.
地球上 g 约为 10 N/kg（或 9.8 N/kg）。重量是以牛顿为单位的力。
xtension is proportional to the applied force, so F = k x, where k is the spring constant.
胡克定律描述弹簧在弹性限度内的伸长：伸长量与所施加的力成正比，即 F = k x，其中 k 是弹簧常数。
3. Density and Pressure | 密度与压强
Density indicates how tightly matter is packed. It is a property of substances independent of sample size.
密度表示物质微粒堆积的紧密程度，是物质本身的属性，与样本大小无关。
density = mass ÷ volume ρ = m ÷ V
The unit of density is kg/m³ or g/cm³. Objects with density less than water (1 g/cm³) float.
密度的单位是 kg/m³ 或 g/cm³。密度小于水（1 g/cm³）的物体在漂浮。
pressure = force ÷ area P = F ÷ A
1 N/m². A sharp knife exerts higher pressure than a blunt one because the area is smaller.
压强以帕斯卡（Pa）为单位，1 Pa = 1 N/m²。锋利的刀比钝刀压强大，因为接触面积更小。
ip P = h ρ g applies where h is depth, but for Year 8 the key concept is depth dependence.
液体中的压强随深度增加，且在同深度处向各个方向作用相等。关系式 P = h ρ g（h为深度）可供参考，但八年级重点在于理解深度对压强的影响。
4. Energy, Work and Power | 能量、功与功率
Energy is the ability to do work. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed.
能量是做功的本领。能量守恒定律指出，能量不能凭空产生或消灭，只能转移或转化。
work done = force × distance moved in direction of force W = F d
Work is measured in joules (J). If you lift a 10 N weight through 2 m, you do 20 J of work.
功以焦耳（J）为单位。将 10 N 的重物提升 2 m，做了 20 J 的功。
kinetic energy = ½ × mass × velocity² KE = ½ m v²
All moving objects possess kinetic energy. Doubling the speed quadruples the kinetic energy.
所有运动物体都具有动能。速度加倍，动能变为原来的四倍。
gravitational potential energy = mass × g × height GPE = m g h
Gravitational potential energy is stored when work is done against gravity. The change in GPE equals m g Δh.
重力势能是在克服重力做功时储存的能量。重力势能的变化量等于 m g Δh。
power = work done ÷ time taken P = W ÷ t
Power is the rate of doing work, measured in watts (W). A 60 W bulb transforms 60 J of electrical energy every second.
功率是做功的速率，单位为瓦特（W）。一只 60 W 的灯泡每秒转化 60 J 电能。
efficiency = (useful output energy ÷ total input energy) × 100%
Efficiency is always less than 100% in real devices because some energy is dissipated as heat or sound.
实际设备中效率始终低于 100%，因为部分能量以热或声的形式耗散。
5. Moments and Equilibrium | 力矩与平衡
A moment is the turning effect of a force about a pivot. Its magnitude depends on both the size of the force and the perpendicular distance from the pivot.
力矩是力绕支点产生的转动效应，其大小取决于力的大小以及力到支点的垂直距离。
moment = force × perpendicular distance from pivot M = F × d
The unit of moment is newton-metre (N m). To increase a moment, you can apply a larger force or use a longer lever arm.
力矩的单位是牛·米（N m）。要增大力矩，可以施加更大的力或使用更长的力臂。
The principle of moments states that for an object in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about the same pivot.
力矩原理指出，物体处于平衡状态时，绕同一支点的顺时针力矩之和等于逆时针力矩之和。
This principle is used to analyse seesaws, levers, and any balanced system. If moments are unbalanced, a resultant torque causes rotation.
该原理用于分析跷跷板、杠杆和各种平衡系统。若力矩不平衡，会产生使物体转动的合力矩。
6. Wave Properties | 波的特性
Waves transfer energy without transferring matter. The speed, frequency, and wavelength of any wave are connected by a fundamental equation.
波传播能量而不传播物质。波速、频率和波长通过基本公式相联系。
wave speed = frequency × wavelength v = f λ
z); wavelength (λ) in metres. The period T = 1/f is the time for one complete oscillation.
频率（f）的单位是赫兹（Hz），波长（λ）的单位是米。周期 T = 1/f 是完成一次全振动所需的时间。
For sound waves, frequency determines pitch and amplitude relates to loudness. Sound travels fastest in solids and cannot travel through a vacuum.
对于声波，频率决定音调，振幅与响度有关。声音在固体中传播最快，不能在真空中传播。
t the angle of incidence equals the angle of reflection (i = r), measured from the normal.
反射定律指出，入射角等于反射角（i = r），角度从法线量起。
Refraction occurs when waves change speed as they cross a boundary between different media, causing a change in direction unless the incidence is normal.
当波通过不同介质界面速度改变时发生折射，除非垂直入射，否则传播方向会发生改变。
7. Electrical Circuits | 电路
Current is the rate of flow of electric charge. The potential difference (voltage) drives the current, and resistance opposes it.
电流是电荷流动的速率。电势差（电压）驱动电流，电阻阻碍电流。
Ohm's law: V = I R
For a given resistor at constant temperature, current is proportional to voltage. Resistance is measured in ohms (Ω).
对于给定温度不变的电阻器，电流与电压成正比。电阻的单位是欧姆（Ω）。
charge = current × time Q = I t
Electric charge is measured in coulombs (C). In a metal conductor, current is a flow of electrons.
电荷的单位是库仑（C）。在金属导体中，电流是电子的流动。
electrical power: P = I V, P = I² R, P = V² ÷ R
Power in an electrical component gives the rate at which it transfers energy. The kilowatt-hour (kWh) is a unit of energy used for mains electricity.
电元件的功率表示其转化能量的速率。千瓦时（kWh）是家庭用电的常用能量单位。
energy transferred = power × time E = P t
where, and total resistance is the sum of individual resistances: Rₜₒₜₐₗ = R₁ + R₂ + ... .
在串联电路中，各处电流相等，总电阻等于各电阻之和：Rₜₒₜₐₗ = R₁ + R₂ + ... 。
cals: 1/Rₚ = 1/R₁ + 1/R₂ + ... . Adding more parallel branches reduces overall resistance.
在并联电路中，各支路两端电压相同，总电阻的倒数等于各支路电阻倒数之和：1/Rₚ = 1/R₁ + 1/R₂ + ... 。增加并联支路会降低总电阻。
8. Magnetism and Electromagnetism | 磁学与电磁
A permanent magnet has a north and south pole. Like poles repel; opposite poles attract. Magnetic field lines point from north to south outside the magnet.
永磁体有北极和南极。同名磁极相互排斥，异名磁极相互吸引。磁体外磁感线从北极指向南极。
The region around a magnet where magnetic forces act is the magnetic field. Field lines are closer together where the field is stronger.
磁体周围存在磁力的区域叫做磁场。磁场强的地方磁感线更密集。
An electromagnet consists of a coil of wire (solenoid) often wrapped around a soft iron core. The magnetic field strength increases with more turns, larger current, or insertion of an iron core.
电磁铁由线圈（螺线管）通常绕在软铁芯上构成。增加匝数、增大电流或插入铁芯都能增强磁场。
Electromagnetic induction is the process of generating a potential difference (and current if the circuit is complete) by moving a conductor in a magnetic field or by changing the magnetic field around it. This is the principle behind generators.
电磁感应是通过导体在磁场中运动或改变导体周围的磁场而产生电势差（若电路闭合则产生电流）的过程。这是发电机的原理。
A current-carrying conductor in a magnetic field experiences a force. Fleming’s left-hand rule helps predict the direction of force, current, and magnetic field for motor effect.
磁场中的通电导体会受到力的作用。弗莱明左手定则可用于判断电动机效应中力、电流和磁场的方向。
9. Thermal Physics Essentials | 热学基础原理
Heat energy transfers from a hotter object to a colder one until thermal equilibrium is reached. There are three main methods: conduction, convection, and radiation.
热能从高温物体传向低温物体，直到达到热平衡。主要传热方式有三种：传导、对流和辐射。
Conduction occurs mainly in solids. Metals are good conductors because free electrons carry energy; insulators like wood or plastic trap heat.
传导主要发生在固体中。金属是热的良导体，因为自由电子携带能量；木材、塑料等绝缘体阻碍热传递。
Convection happens in fluids (liquids and gases). When a fluid is heated, it expands, becomes less dense, and rises, while cooler fluid sinks, creating a convection current.
对流发生在流体（液体和气体）中。流体受热膨胀、密度变小而上升，较冷的流体下沉，形成对流循环。
Infrared radiation is the transfer of heat by electromagnetic waves. It does not require a medium and can travel through a vacuum, which is how the Sun's energy reaches Earth.
红外辐射是通过电磁波传递热量，不需要介质，可以在真空中传播，太阳的能量就是由此到达地球。
Dark, matt surfaces are better emitters and absorbers of radiation than shiny, light-coloured surfaces. This principle is used in designing solar panels and cooling systems.
暗色粗糙表面比光亮浅色表面更容易吸收和发射辐射。这一原理应用于太阳能板和冷却系统的设计。
Most materials expand when heated and contract when cooled. Water is unusual because it expands when freezing, which is why ice floats.
大多数材料热胀冷缩。水是一个例外，它在结冰时膨胀，所以冰浮在水面上。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图