📚 Year 7 WJEC Physics: Key Knowledge Review | 核心知识点梳理
Physics in Year 7 covers the fundamental concepts that explain how the universe works, from the smallest particles to the largest galaxies. This revision guide summarises the core topics of the WJEC curriculum, including energy, forces, electricity, magnetism, waves, and the particle model.
七年级物理涵盖了解释宇宙运作的基础概念，从最小的粒子到最大的星系。这份复习指南概括了WJEC课程的核心主题，包括能量、力、电、磁、波以及粒子模型。
1. What is Physics? | 什么是物理？
Physics is the study of matter, energy, and the interactions between them. It helps us understand how things move, why objects fall, how light travels, and much more.
物理是研究物质、能量及其相互作用的学科。它帮助我们理解物体如何运动，物体为什么会下落，光如何传播，等等。
2. Energy | 能量
Energy is the ability to do work. It exists in many forms: kinetic (movement), thermal (heat), sound, light, electrical, and gravitational potential. Energy can be transferred from one store to another, but it is never created or destroyed — this is the principle of conservation of energy. In many devices, some energy is transferred to thermal stores and is considered wasted.
能量是做功的能力。它有许多形式：动能（运动）、热（内）能、声能、光能、电能和重力势能。能量可以从一个储存库转移到另一个储存库，但它永远不会被创造或消灭——这就是能量守恒原理。在许多设备中，部分能量会传递到热能储存库，被视为浪费的能量。
For example, a toaster transfers electrical energy into thermal energy and light. A solar panel transfers light energy into electrical energy.
例如，烤面包机将电能转化为热能和光能；太阳能电池板将光能转化为电能。
Energy resources are divided into renewable and non-renewable:
- Renewable: solar, wind, wave, tidal, hydroelectric, geothermal, biomass.
- Non-renewable: fossil fuels (coal, oil, natural gas) and nuclear fuel.
能源资源分为可再生和不可再生：
- 可再生能源：太阳能、风能、波浪能、潮汐能、水能、地热能、生物质能。
- 不可再生能源：化石燃料（煤、石油、天然气）以及核燃料。
3. Forces | 力
Forces are pushes or pulls that can change the speed, direction, or shape of an object. Forces are measured in newtons (N). There are two main types of force:
- Contact forces require objects to touch, e.g. friction, air resistance, tension.
- Non-contact forces act over a distance, e.g. gravity, magnetic force, electrostatic force.
力是推或拉，可以改变物体的速度、方向或形状。力的单位是牛顿（N）。力主要分为两类：
- 接触力需要物体接触，如摩擦力、空气阻力、张力。
- 非接触力可以隔空作用，如重力、磁力、静电力。
If forces on an object are balanced, the object remains stationary or moves at constant speed. Unbalanced forces cause a change in motion — acceleration or deceleration.
如果作用在物体上的力是平衡的，物体会保持静止或匀速运动。不平衡的力会导致运动状态改变——加速或减速。
4. Gravity and Friction | 重力与摩擦力
Gravity is a non-contact force that attracts two masses towards each other. On Earth, gravity pulls objects towards the centre of the planet. Weight is the force due to gravity and is calculated using the formula:
Weight (N) = mass (kg) × gravitational field strength (N/kg)
重力是一种吸引两物体相互靠近的非接触力。在地球上，重力将物体拉向地心。重量是由重力产生的力，计算公式为：
重量（N）= 质量（kg）× 重力场强度（N/kg）
On Earth, the gravitational field strength, g, is approximately 10 N/kg. So a 5 kg object weighs 50 N.
在地球上，重力场强度 g 约为 10 N/kg，因此一个 5 kg 的物体重量为 50 N。
Friction is a contact force that opposes motion between two surfaces in contact. It can be useful (e.g. gripping shoes) or wasteful (e.g. causing parts in an engine to wear). Air resistance and water resistance are types of friction acting on objects moving through fluids.
摩擦力是阻碍两个接触表面相对运动的接触力。它可能是有用的（例如鞋子的抓地力），也可能造成浪费（例如导致发动机零件磨损）。空气阻力和水阻力是物体在流体中运动时产生的摩擦。
5. Motion and Speed | 运动与速度
Speed tells us how fast an object travels. It is calculated by dividing the distance travelled by the time taken:
Speed = distance ÷ time
速度表示物体运动的快慢。它由行驶距离除以所用时间计算得出：
速度 = 距离 ÷ 时间
Common units of speed are metres per second (m/s) and kilometres per hour (km/h).
常见的速度单位是米每秒（m/s）和公里每小时（km/h）。
A distance–time graph helps visualise motion:
- A horizontal line means the object is stationary.
- A straight sloping line means the object is moving at constant speed.
- A steeper slope indicates a faster speed.
距离–时间图可直观展示运动状态：
- 水平直线表示物体静止。
- 倾斜直线表示物体匀速运动。
- 斜率越大表示速度越快。
6. Electricity Basics | 电学基础
An electric circuit must be a complete loop for current to flow. Current (I) is the flow of electric charge, measured in amperes or amps (A). Voltage (V), measured in volts (V), is the 'push' or energy per unit charge that drives the current around a circuit.
电路必须是完整回路才能让电流流动。电流（I）是电荷的流动，单位是安培（A）。电压（V）是推动电流绕行电路的压力或每单位电荷的能量，单位是伏特（V）。
There are two basic circuit arrangements:
- Series circuit: components connected in a single loop. Current is the same everywhere, but voltage is shared across components.
- Parallel circuit: components are connected on separate branches. Voltage is the same across each branch, but current can split.
有两种基本电路连接方式：
- 串联电路：元件连接在单一环路中。各处电流相同，但电压在元件间分配。
- 并联电路：元件连接在独立的支路上。各支路电压相同，但电流可能分流。
Common circuit symbols should be drawn clearly: a single cell, battery, bulb, switch, resistor, and ammeter/voltmeter.
应能清晰画出常见的电路符号：单个电池、电池组、灯泡、开关、电阻、电流表和电压表。
7. Magnetism | 磁学
Magnets have two poles: north (N) and south (S). Like poles repel each other; unlike poles attract. Only a few materials are magnetic — mainly iron, nickel, cobalt, and steel (an alloy of iron).
磁体有两个极：北极（N）和南极（S）。同极相斥，异极相吸。只有少数材料具有磁性——主要是铁、镍、钴和钢（铁的合金）。
A magnetic field is the region around a magnet where magnetic forces are felt. Field lines show the direction: they run from the north pole to the south pole outside the magnet, and are closer together where the field is stronger.
磁场是磁体周围能感受到磁力的区域。磁感线显示方向：在磁体外从北极指向南极，磁感线越密集表示磁场越强。
The Earth has its own magnetic field, which is why a compass needle points towards the magnetic north pole.
地球本身具有磁场，这就是指南针指向磁北极的原因。
8. Waves: Sound | 波：声音
Sound is produced by vibrating objects. These vibrations travel as longitudinal waves, in which particles vibrate back and forth in the same direction as the wave travels. Sound needs a medium (solid, liquid, or gas) to travel; it cannot travel through a vacuum.
声音由振动物体产生。这些振动以纵波形式传播，质点沿传播方向来回振动。声音需要介质（固体、液体或气体）才能传播，不能在真空中传播。
The speed of sound in air is about 340 m/s. It travels faster in solids and liquids than in gases.
声音在空气中的传播速度约为 340 m/s。它在固体和液体中比在气体中传播得更快。
Two key properties of sound are:
- Pitch — how high or low a sound is, determined by the frequency (number of vibrations per second, measured in hertz, Hz).
- Loudness — how loud or quiet a sound is, determined by the amplitude of the wave.
声音的两个关键属性：
- 音调——声音的高低，由频率（每秒振动次数，单位赫兹 Hz）决定。
- 响度——声音的大小，由波的振幅决定。
9. Waves: Light | 波：光
Light is a transverse wave that can travel through a vacuum. It moves in straight lines at an incredible speed — approximately 300,000 km/s in a vacuum.
光是横波，可以在真空中传播。它以令人难以置信的速度沿直线传播——真空中约 300,000 km/s。
We see objects because light reflects off them and enters our eyes. The law of reflection states: the angle of incidence equals the angle of reflection, measured from an imaginary normal line at right angles to the surface.
我们能看到物体是因为光从物体表面反射进入眼睛。反射定律表明：入射角等于反射角，均从垂直于表面的假想法线测量。
White light is actually a mixture of colours (the visible spectrum: red, orange, yellow, green, blue, indigo, violet). This can be demonstrated by passing light through a prism, which disperses it into a rainbow.
白光实际上是一种颜色混合体（可见光谱：红、橙、黄、绿、蓝、靛、紫）。让光通过棱镜就可以看到色散形成的彩虹。
10. The Particle Model and States of Matter | 粒子模型与物质状态
All substances are made of tiny, constantly moving particles. The particle model explains the properties of solids, liquids, and gases:
- Solid: particles closely packed in a fixed, regular pattern; they vibrate in place.
- Liquid: particles close together but able to move past each other; they take the shape of the container.
- Gas: particles far apart, moving rapidly in all directions; they fill the available space.
所有物质都由微小的、不断运动的粒子构成。粒子模型解释了固体、液体和气体的性质：
- 固体：粒子紧密排列成固定的规则结构，仅在原位振动。
- 液体：粒子彼此靠近但可以相互滑动，呈现容器的形状。
- 气体：粒子间距很大，向各个方向快速运动，充满整个空间。
Changes of state are physical changes that involve energy transfer without changing the chemical nature of the substance:
- Melting (solid to liquid) and boiling/evaporating (liquid to gas) require energy input.
- Freezing (liquid to solid) and condensing (gas to liquid) release energy.
物态变化是物理变化，涉及能量传递但不改变化学性质：
- 熔化（固体变液体）和沸腾/蒸发（液体变气体）需要吸收能量。
- 凝固（液体变固体）和冷凝（气体变液体）会释放能量。
11. Space and the Solar System | 太空与太阳系
Our Solar System consists of the Sun, eight planets, their moons, dwarf planets (like Pluto), asteroids, and comets. The Sun is a star at the centre, held together by gravity.
我们的太阳系由太阳、八大行星及各自的卫星、矮行星（如冥王星）、小行星和彗星组成。太阳是位于中心、由引力束缚的恒星。
The Earth orbits the Sun once every 365 days (one year) and spins on its axis once every 24 hours (one day). This rotation causes day and night, while the tilt of Earth's axis leads to seasons.
地球每 365 天绕太阳公转一圈（一年），每 24 小时自转一圈（一天）。自转产生了昼夜，地轴的倾斜则导致了季节变化。
The Moon orbits the Earth approximately every 28 days. Gravity is the force that keeps planets in orbit around the Sun and moons in orbit around planets.
月球约每 28 天绕地球一圈。引力是维持行星绕太阳、卫星绕行星运行的力。
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