📚 Year 9 Edexcel Physics: Core Knowledge Review | Year 9 Edexcel 物理：核心知识点梳理
Year 9 Edexcel Physics builds a solid foundation in the physical world, linking everyday observations to scientific principles. From the motion of objects to the behaviour of electric circuits and the nature of waves, this stage introduces key concepts that will be essential for IGCSE and beyond. A clear understanding of energy, forces, matter, and practical methods is the goal of this review.
Year 9 Edexcel 物理为理解物理世界打下坚实基础，将日常观察与科学原理联系起来。从物体的运动到电路的行为，再到波的本质，这一阶段介绍了对于 IGCSE 及以后学习至关重要的核心概念。本次梳理旨在帮助你清晰掌握能量、力、物质以及实验方法。
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 vector quantities, meaning they have both magnitude and direction, while distance and speed are scalars. The unit of force is the newton (N). Contact forces, such as friction and tension, require physical touch, whereas non‑contact forces like gravity and magnetism act over a distance.
力是一种推或拉，可以改变物体的速度、方向或形状。力是矢量，既有大小又有方向，而距离和速率是标量。力的单位是牛顿 (N)。接触力，如摩擦力和张力，需要物体相互接触；非接触力，如重力和磁力，则能够在隔空的情况下作用。
e in velocity; it is calculated as acceleration = change in velocity / time. On a distance– h, a straight line represents constant speed, and the gradient gives the speed. A velocity– h shows acceleration as its gradient, and the area under the line represents displacement.
物体的运动可以用 速度 = 距离 ÷ 时间 来描述。当速度发生变化时，就会产生加速度，计算方法是 加速度 = 速度变化量 ÷ 时间。在距离‑时间图上，直线表示匀速，斜率代表速度。速度‑时间图的斜率表示加速度，图线下的面积代表位移。
celeration (F = m a); and every action has an equal and opposite reaction. Resultant force is the single force that has the same effect as all forces combined.
牛顿三定律支配着运动：物体在没有合力作用时保持静止或匀速直线运动（惯性）；力等于质量乘以加速度 (F = m a)；每一个作用力都有一个等大反向的反作用力。合力是能产生与所有分力相同效果的那个单一的力。
2. Energy Stores and Transfers | 能量的储存与转移
Energy is the capacity to do work and is measured in joules (J). There are several energy stores: kinetic (movement), gravitational potential (height), elastic potential (stretched or compressed materials), thermal (internal energy), chemical (fuels, food), and nuclear. Energy can be transferred between stores via four pathways: by forces doing mechanical work, by heating, by electric currents, and by radiation (light and sound waves).
能量是做功的能力，单位是焦耳 (J)。能量可以储存在多种形式中：动能（运动）、重力势能（高度）、弹性势能（拉伸或压缩）、热能（内能）、化学能（燃料、食物）和核能。能量可以通过四种途径在不同储存形式之间转移：力做机械功、加热、电流以及辐射（光波和声波）。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another. In real transfers, some energy is always dissipated as thermal energy, which spreads out and becomes less useful. Sankey diagrams are used to represent energy transfers, with arrow widths proportional to the energy amounts.
能量守恒定律指出，能量不会凭空产生或消失，只会从一种储存形式转移到另一种。在实际转移过程中，总有一部分能量耗散为热能，散开并变得不再有用。桑基图常用于表示能量转移，图中箭头的宽度与能量的大小成正比。
3. Work and Power | 功与功率
oved: W = F × d. Work and energy share the same unit, the joule. For example, lifting a 10 N weight through 2 m requires 20 J of work.
当力使物体沿力的方向移动时，我们就说力做了功。做功的大小等于力乘以移动的距离：W = F × d。功和能量使用相同的单位，焦耳。例如，将一个 10 N 的重物举高 2 m 需要做 20 J 的功。
nergy is transferred: P = W / t (or P = E / t). The unit of power is the watt (W), where 1 W = 1 J/s. A more powerful motor transfers the same amount of energy in less time.
功率是做功或转移能量的快慢程度：P = W ÷ t（或 P = E ÷ t）。功率的单位是瓦特 (W)，1 W 等于 1 J/s。功率越大的电动机，转移同等能量所需的时间越短。
4. Electricity: Circuits and Current | 电学：电路与电流
An electric circuit must be a complete loop for current to flow. Standard circuit symbols are used to represent components: a cell, battery, lamp, switch, resistor, variable resistor, ammeter, voltmeter, and diode. Electric current is the rate of flow of charge, measured in amperes (A) with an ammeter connected in series.
电路必须是一个完整的回路，电流才能流动。我们使用标准电路符号来表示各元件：电池、电池组、灯泡、开关、电阻器、可变电阻器、电流表、电压表和二极管。电流是电荷流动的速率，单位是安培 (A)，用串联的电流表测量。
In a series circuit, the current is the same at all points, and the total resistance is the sum of individual resistances. In a parallel circuit, the current splits at junctions, and the total resistance is less than the smallest individual resistance. Charge is conserved, so the sum of currents entering a junction equals the sum leaving it.
在串联电路中，各处电流相等，总电阻等于各个电阻之和。在并联电路中，电流在节点处分流，总电阻小于最小的单个电阻。电荷是守恒的，因此流入某节点的电流之和等于流出该节点的电流之和。
5. Voltage and Resistance | 电压与电阻
Voltage, or potential difference, is the energy transferred per unit of charge and is measured in volts (V) with a voltmeter connected in parallel. It drives the current through a component. Resistance measures how difficult it is for current to pass through; the unit is the ohm (Ω).
电压，即电势差，是单位电荷所转移的能量，单位是伏特 (V)，用并联的电压表测量。电压驱动电流流过元件。电阻衡量电流通过的难易程度，单位是欧姆 (Ω)。
Resistance = Voltage / Current → R = V / I
Ohm’s law states that, at constant temperature, the current through a resistor is directly proportional to the voltage across it, so its resistance is constant. The resistance of a wire depends on its length, cross‑sectional area and material. In a series circuit, the supply voltage is shared between components; in parallel, each branch receives the full supply voltage.
欧姆定律指出，在温度不变时，通过电阻器的电流与它两端的电压成正比，因此其电阻恒定。导线的电阻取决于长度、横截面积和材料。在串联电路中，电源电压在元件之间分配；在并联电路中，每个支路都得到全部的电源电压。
6. Waves: Properties and Types | 波的性质与类型
Waves transfer energy without transferring matter. There are two main types: transverse waves, where oscillations are perpendicular to the direction of energy transfer (e.g. light, water waves), and longitudinal waves, where oscillations are parallel to the direction (e.g. sound, seismic P‑waves).
波可以传递能量，但不传递物质。主要分为两类：横波，振动方向与能量传递方向垂直（如光、水波）；纵波，振动方向与能量传递方向平行（如声音、地震 P 波）。
Key wave properties include amplitude (maximum displacement from rest), wavelength (distance between two identical points on consecutive waves), frequency (number of waves per second, in hertz, Hz), and period (time for one complete wave). The wave speed equation links them:
波的主要特性包括振幅（离开平衡位置的最大位移）、波长（相邻两波对应点之间的距离）、频率（每秒的波数，单位赫兹 Hz）和周期（完成一个完整波所需的时间）。它们之间的关系由波速方程表示：
Wave speed = frequency × wavelength → v = f λ
For all waves, when they travel from one medium to another, their speed and wavelength may change, but the frequency stays the same.
所有波从一种介质进入另一种介质时，波速和波长可能改变，但频率保持不变。
7. Light and Sound | 光与声
Light is a transverse electromagnetic wave that can travel through a vacuum. The law of reflection states that the angle of incidence equals the angle of reflection, measured from the normal. Refraction occurs when light passes into a different medium, changing speed and direction. Lenses and prisms make use of refraction.
光是横波，属于电磁波，可以在真空中传播。反射定律指出，入射角等于反射角，两角都从法线量起。当光进入另一种介质时会发生折射，改变速度和方向。透镜和棱镜都利用折射现象。
Sound is a longitudinal wave that travels by vibrating particles. It cannot travel through a vacuum. The speed of sound in air is about 340 m/s. The human ear detects sound when vibrations are transmitted to the cochlea. Echoes are reflected sound waves; a delay of 0.1 s or more is needed for a distinct echo.
声音是一种纵波，依靠粒子振动传播，不能在真空中传播。声音在空气中的速度约为 340 m/s。人耳通过振动传至耳蜗来探测声音。回声是反射的声波；要让人感受到明显的回声，延迟通常需要 0.1 s 或以上。
8. Matter: Particle Model and States | 物质：粒子模型与状态
The particle model explains the behaviour of solids, liquids and gases. In solids, particles are closely packed in a regular arrangement and vibrate in fixed positions. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move rapidly in all directions.
粒子模型可以解释固体、液体和气体的行为。固体中，粒子紧密排列，有规则的分布，并在固定位置振动。液体中，粒子仍较接近，但能相对滑动。气体中，粒子相隔很远，朝各个方向快速运动。
Changes of state include melting, freezing, boiling, condensing and sublimation. During a change of state, temperature remains constant because energy is used to break or form bonds rather than to raise kinetic energy. This energy is called latent heat. Brownian motion—the random movement of smoke or pollen grains—provides evidence for the continuous motion of particles.
状态变化包括熔化、凝固、沸腾、凝结和升华。在状态变化过程中，温度保持恒定，因为能量用于打破或形成键，而不是增加动能。这部分能量称为潜热。布朗运动——烟尘或花粉颗粒的无规则运动——为粒子持续运动提供了证据。
9. Density and Pressure | 密度与压强
Density is the mass per unit volume of a substance. The formula is:
密度是单位体积物质的质量。公式为：
Density = mass / volume → ρ = m / V
The unit is kg/m³ or g/cm³. The density of water is 1 g/cm³ (1000 kg/m³). Objects with a density lower than a fluid float, while denser objects sink.
单位是 kg/m³ 或 g/cm³。水的密度是 1 g/cm³ (1000 kg/m³)。密度小于流体的物体会浮起，密度大的则会下沉。
al (Pa) or N/m². A force applied over a smaller area produces a higher pressure. In liquids, pressure increases with depth and acts equally in all directions. Atmospheric pressure decreases with altitude and is measured with a barometer.
压强是单位面积上所受的压力：压强 = 压力 ÷ 面积，单位是帕斯卡 (Pa) 或 N/m²。相同大小的力作用在更小的面积上会产生更大的压强。在液体中，压强随深度增加，且向各个方向均匀作用。大气压强随高度增加而降低，可用气压计测量。
10. Magnetism and Electromagnetism | 磁学与电磁学
Certain materials, such as iron, cobalt and nickel, are ferromagnetic. A permanent magnet has a north and a south pole; like poles repel, unlike poles attract. Magnetic field lines show the direction of the magnetic force, pointing from north to south outside the magnet. The Earth itself behaves as a giant magnet.
铁、钴、镍等材料具有铁磁性。永磁体有 N 极和 S 极；同名磁极相互排斥，异名磁极相互吸引。磁感线显示了磁力的方向，在磁体外从 N 极指向 S 极。地球本身就像一个巨大的磁体。
An electromagnet is created by passing current through a coil of wire (solenoid), often wrapped around a soft iron core. The magnetic field strength can be increased by increasing the current, adding more turns to the coil, or using an iron core. Electromagnets are used in relays, electric bells, and lifting magnets in scrapyards.
电磁铁是通过使电流流过线圈（螺线管）而产生的，通常线圈缠绕在软铁芯上。增大电流、增加线圈匝数或使用铁芯都可以增强磁场强度。电磁铁广泛应用于继电器、电铃和废料场的起重磁铁中。
11. Practical Skills and Data Handling | 实验技能与数据处理
In Year 9 physics, investigations follow a scientific method: identify independent, dependent and control variables; take repeated readings to improve reliability; and present results in well‑labelled tables. Graphs are plotted with the independent variable on the x‑axis and the dependent variable on the y‑axis, using appropriate scales.
在 Year 9 物理中，研究遵循科学方法：确定自变量、因变量和控制变量；多次读数以提高可靠性；并用标注清晰的表格展示结果。绘图时以自变量为 x 轴、因变量为 y 轴，选用合适的刻度。
The gradient of a straight‑line graph represents a physical quantity (e.g. speed on a distance–time graph). Calculations are performed using standard formulae, and answers are given with correct units and an appropriate number of significant figures. Evaluating the method involves identifying sources of error, such as parallax or thermal loss, and suggesting improvements.
直线图的斜率代表某个物理量（如距离‑时间图中的速度）。计算时使用标准公式，答案要带有正确的单位和适当数量的有效数字。评价实验方法时，要能识别误差来源（如视差或热损失），并提出改进建议。
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