📚 Year 9 WJEC Physics: Core Knowledge Review | 九年级 WJEC 物理：核心知识点梳理
This guide brings together the most important physics topics that Year 9 students encounter in the WJEC curriculum. A secure grasp of these core areas will support progress into GCSE and beyond, linking everyday observations to scientific principles.
本指南汇集了九年级 WJEC 物理课程中最重要的主题。扎实掌握这些核心内容将为 GCSE 乃至更高阶段的学习提供支撑，把日常观察与科学原理紧密联系起来。
1. Forces and Motion | 力与运动
Forces are pushes or pulls that can change an object's speed, direction, or shape. They are measured in newtons (N) and often represented by arrows in free-body diagrams.
力是能改变物体速度、方向或形状的推或拉。力的单位是牛顿（N），常用箭头在受力示意图中表示。
Average speed is the total distance travelled divided by the total time taken. The relationship is:
平均速度等于移动的总距离除以所用总时间。关系式为：
v = d / t
where v is speed (m/s), d is distance (m), and t is time (s). Acceleration tells us how quickly velocity changes.
其中 v 为速度（m/s），d 为距离（m），t 为时间（s）。加速度表示速度变化的快慢。
a = Δv / Δt
The unit of acceleration is metres per second squared (m/s²). A resultant (net) force causes acceleration according to Newton's Second Law, but Year 9 often focuses on balanced and unbalanced forces. When forces are balanced, an object remains at rest or moves at constant velocity.
加速度的单位是米每二次方秒（m/s²）。合外力引起加速度，符合牛顿第二定律，不过九年级主要关注平衡力与非平衡力。当力平衡时，物体会保持静止或匀速直线运动。
Weight is the gravitational force on an object and differs from mass. Weight can be calculated using:
重量是作用在物体上的重力，与质量不同。重量可用下式计算：
W = m × g
to 10 N/kg). Friction and air resistance oppose motion and can be reduced by streamlining.
地球的重力场强度 g ≈ 9.8 N/kg（常取 10 N/kg）。摩擦力和空气阻力阻碍运动，可通过流线型设计减小。
2. Energy Resources and Transfers | 能源与能量转移
Energy exists in many forms: kinetic, gravitational potential, thermal (internal), chemical, elastic potential, and nuclear. Energy is measured in joules (J).
能量有多种形式：动能、重力势能、热（内）能、化学能、弹性势能和核能。能量的单位是焦耳（J）。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or converted from one form to another. In any process, the total energy remains constant.
能量守恒定律指出，能量既不会凭空产生也不会凭空消失，只会从一种形式转移或转化为另一种形式。在任何过程中，总能量保持不变。
Two particularly useful kinetic equations that are often introduced in Year 9 are:
九年级常引入的两个重要动能和势能方程是：
Eₖ = ½mv²
Eₚ = mgh
Here Eₖ is kinetic energy, m is mass, v is speed, Eₚ is change in gravitational potential energy, and h is change in height. These equations help quantify energy transfers in falling objects or roller coasters.
其中 Eₖ 为动能，m 为质量，v 为速度，Eₚ 为重力势能变化量，h 为高度变化量。这些方程有助于定量描述下落物体或过山车中的能量转移。
Work done is equal to the force multiplied by the distance moved in the direction of the force:
做功等于力乘以在力的方向上移动的距离：
W = F × d
hich work is done or energy is transferred: P = W / t or P = E / t, measured in watts (W).
功率是做功或能量转移的速率：P = W / t 或 P = E / t，单位为瓦特（W）。
Energy resources are classified as renewable (solar, wind, tidal, hydroelectric, biomass) or non-renewable (fossil fuels, nuclear). WJEC expects students to discuss environmental impacts and energy security.
能源可分为可再生（太阳能、风能、潮汐能、水力发电、生物质能）和不可再生（化石燃料、核能）两大类。WJEC 希望学生能够讨论环境影响和能源安全问题。
3. Electricity and Circuits | 电与电路
Electric current is the flow of electric charge, measured in amperes (A). For conventional current, we consider the direction from positive to negative. Voltage (potential difference) is the energy transferred per unit charge and is measured in volts (V).
电流是电荷的流动，单位为安培（A）。常规电流方向规定为正电荷移动的方向。电压（电势差）是单位电荷转移的能量，单位为伏特（V）。
Resistance opposes the flow of current and is measured in ohms (Ω). The relationship between voltage, current and resistance is given by Ohm's Law:
电阻阻碍电流的流动，单位为欧姆（Ω）。电压、电流和电阻的关系由欧姆定律给出：
V = I × R
Many conductors obey Ohm's Law only if temperature remains constant. Factors affecting resistance include the length, cross-sectional area and material of the wire.
许多导体仅在温度不变时才遵循欧姆定律。影响电阻的因素包括导线的长度、横截面积和材料。
Students must recognise and draw standard circuit symbols: cells, batteries, switches, lamps, fixed resistors, variable resistors, ammeters, voltmeters, fuses, and diodes. In WJEC assessments, neat diagrams are essential.
学生必须识别并绘制标准电路符号：电池、开关、灯泡、定值电阻、可变电阻、电流表、电压表、熔断器和二极管等。在 WJEC 考试中，整洁的电路图至关重要。
In series circuits, the current is the same everywhere, and the total resistance is the sum of individual resistances. In parallel circuits, the voltage across each branch is the same, while current splits and total resistance decreases compared to the smallest branch resistance.
串联电路中各处电流相等，总电阻为各电阻之和。并联电路中各支路电压相同，电流分流，总电阻比最小支路电阻还要小。
Safety devices such as fuses and circuit breakers protect circuits by breaking when current becomes too high. Double insulation and earthing are also key concepts in domestic electricity.
熔断器和断路器这类安全装置会在电流过大时断开电路。双重绝缘和接地也是家庭用电中的重要概念。
4. Waves: Sound and Light | 波：声音与光
Waves transfer energy without transferring matter. There are two main types: transverse waves, where the particle oscillation is perpendicular to the direction of energy transfer, and longitudinal waves, where the oscillation is parallel.
波传递能量而不传递物质。主要的两种类型是：横波，质点振动方向与能量传递方向垂直；纵波，质点振动方向与能量传递方向平行。
| Transverse Waves | Longitudinal Waves |
| Examples: light, water ripples, seismic S-waves | Examples: sound, ultrasound, seismic P-waves |
| Particles move up and down | Particles move back and forth, creating compressions and rarefactions |
横波例如光、水波、地震 S 波；纵波例如声音、超声波、地震 P 波，纵波形成疏密部。
The wave speed equation links frequency and wavelength:
波速公式将频率与波长联系起来：
v = fλ
(m). Frequency is the number of complete oscillations per second, and the period T = 1/f.
其中 v 为波速（m/s），f 为频率（Hz），λ（lambda）为波长（m）。频率是每秒完整振动的次数，周期 T = 1/f。
Sound is produced by vibrating objects and travels fastest in solids, then liquids, and slowest in gases. The human hearing range is approximately 20 Hz to 20 000 Hz. Ultrasound, above this range, has medical and industrial uses.
声音由物体振动产生，在固体中最快传播，液体次之，气体中最慢。人类听觉范围约为 20 Hz 到 20000 Hz。高于此范围的超声波可用于医疗和工业领域。
Light can be described as a transverse electromagnetic wave. It travels in straight lines, leading to shadows and eclipses. Reflection obeys the law: angle of incidence equals angle of reflection. Refraction occurs when light changes speed at a boundary, bending unless it strikes along the normal.
光可看作横电磁波，沿直线传播，形成影子和日食月食。反射遵守入射角等于反射角的定律。折射发生在光穿过界面速度改变时，除非沿法线入射，否则光线会发生弯曲。
5. Particle Model of Matter | 物质的粒子模型
The particle model explains the properties of solids, liquids, and gases. All matter consists of tiny particles that are constantly in motion. The strength of forces between particles determines the state.
粒子模型解释了固体、液体和气体的性质。所有物质都由不断运动的微小粒子组成。粒子间作用力的强弱决定了物态。
- Solids: tightly packed, regular arrangement, particles vibrate in fixed positions.
- Liquids: particles close but can slide past each other, taking the shape of the container.
- Gases: widely spaced, random fast motion, filling the available volume.
- 固体：粒子紧密排列，规则整齐，在固定位置振动。
- 液体：粒子靠近但可相互滑动，呈容器形状。
- 气体：粒子间隔大，快速无规则运动，充满整个空间。
Density measures how much mass is packed into a given volume. The equation is:
密度衡量单位体积内所含质量的大小。公式为：
ρ = m / V
where ρ is density (kg/m³ or g/cm³), m is mass (kg or g), and V is volume (m³ or cm³). Regular solids can be measured with a ruler; irregular solids use a displacement method.
其中 ρ 为密度（kg/m³ 或 g/cm³），m 为质量（kg 或 g），V 为体积（m³ 或 cm³）。规则固体可用刻度尺测量，不规则固体采用排水法。
Changes of state—melting, freezing, boiling, condensing, and sublimation—are reversible physical changes. Mass is conserved during these changes, but the arrangement and motion of particles alter. The internal energy changes even when temperature stays constant during a change of state.
物态变化——熔化、凝固、沸腾、凝结和升华——都是可逆的物理变化。变化过程中质量守恒，但粒子的排列和运动方式发生改变。即使物态变化时温度保持不变，内能仍会发生变化。
6. Pressure in Fluids | 流体压强
Pressure is the force exerted per unit area. A smaller contact area produces a greater pressure for the same force, explaining why sharp objects cut more easily.
压强是单位面积上受到的压力。在力相同的情况下，接触面积越小，压强越大，这解释了为什么锋利物体更容易切割。
p = F / A
1 Pa = 1 N/m². High-heeled shoes or drawing pins demonstrate everyday effects of pressure.
压强单位为帕斯卡（Pa），1 Pa = 1 N/m²。高跟鞋或图钉等现象体现了压强的日常效应。
In liquids, pressure increases with depth because the weight of the liquid above causes a greater force. The pressure at a point in a liquid can be found using:
液体中压强随深度增加，因为上方液体的重量产生了更大的力。液体中某点的压强可用下式计算：
p = hρg
where h is depth (m), ρ is density of the liquid (kg/m³), and g is gravitational field strength. Pressure acts in all directions in a liquid, which is why dams are thicker at the bottom.
其中 h 为深度（m），ρ 为液体密度（kg/m³），g 为重力场强度。液体压强向各个方向传递，因此水坝底部需要更厚。
Gas pressure arises from countless collisions of particles with the walls of their container. Increasing temperature increases the kinetic energy of particles, leading to more frequent and harder collisions, thus raising pressure (as long as volume is fixed). Atmospheric pressure decreases with altitude.
气体压强源于大量粒子与容器壁的碰撞。温度升高会使粒子动能增大，碰撞更频繁、更猛烈，从而增大压强（体积不变前提下）。大气压强随海拔升高而降低。
7. Magnetism and Electromagnetism | 磁学与电磁学
Magnets have north and south poles; like poles repel, unlike poles attract. Only a few materials—iron, cobalt, nickel, and their alloys—are ferromagnetic and can be permanently magnetised.
磁铁有北极和南极，同名磁极相斥，异名磁极相吸。只有铁、钴、镍及其合金等少数材料是铁磁性的，可以被永久磁化。
A magnetic field is the region around a magnet where magnetic forces are experienced. Field lines run from north to south, are closer together near the poles, and never cross. Plotting compasses trace these lines.
磁场是磁体周围受到磁力作用的区域。磁感线从北极指向南极，在两极附近较密集且永不相交。小磁针可描绘出磁感线。
An electromagnet is made by passing an electric current through a coil of wire (solenoid), often with a soft iron core. The magnetic field can be made much stronger by increasing the current, adding more turns, or using an iron core. Unlike permanent magnets, electromagnets can be switched on and off and reversed.
电磁铁是通过线圈（螺线管）通电而产生的，通常加入软铁芯。增加电流、增加线圈匝数或使用铁芯都能显著增强磁场。与永磁体不同，电磁铁可以开关和反向。
Applications include electric bells, relays, loudspeakers, and magnetic levitation trains. WJEC questions often ask students to explain how an electric bell works step by step.
应用实例包括电铃、继电器、扬声器和磁悬浮列车。WJEC 常要求学生逐步解释电铃的工作原理。
8. Space Physics | 空间物理学
Our solar system consists of the Sun, eight planets, their moons, dwarf planets, asteroids, and comets. Gravitational attraction between the Sun and planets keeps them in their nearly circular orbits.
我们的太阳系由太阳、八大行星、它们的卫星、矮行星、小行星和彗星组成。太阳与行星之间的万有引力使它们保持在近似圆形的轨道上。
The Earth rotates on its axis once every 24 hours, causing day and night. Its orbit around the Sun takes about 365.25 days, giving the year. The tilt of Earth's axis (approximately 23.5°) is responsible for the seasons as different hemispheres receive varying amounts of sunlight.
地球每 24 小时自转一周，形成昼夜交替；绕太阳公转周期约为 365.25 天，形成一年。地轴倾斜约 23.5°，使不同半球获得不同的日照量，从而产生四季。
Natural satellites, like the Moon, orbit planets; artificial satellites are used for communication, navigation, and Earth observation. The force of gravity provides the centripetal force needed to keep satellites in orbit. A geostationary satellite orbits once every 24 hours and stays above the same point on the equator.
像月球这样的天然卫星绕行星运行；人造卫星用于通信、导航和地球观测。重力提供了卫星在轨运动所需的向心力。地球同步卫星每 24 小时绕行一圈，固定在赤道某点上方。
Distances in space are so vast that astronomers use the light-year— ten introduces the Big Bang theory as the origin of the Universe, supported by red-shift evidence showing galaxies moving away from us.
宇宙距离极为遥远，天文学家使用光年——光在一年内传播的距离（约 9.46×10¹² km）。WJEC 九年级常引入宇宙起源的大爆炸理论，红移证据表明星系正在远离我们，支持这一理论。
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