📚 Year 7 CAIE Physics: Core Knowledge Review | Year 7 CAIE 物理：核心知识点梳理
In Year 7 CAIE Physics, you will build a strong foundation by exploring how scientists investigate the world, how things move, and how different forms of energy and matter behave. This article organises all the core knowledge you need to master, from measurements and forces to electricity and space. It will help you revise key concepts confidently for your tests.
在Year 7 CAIE物理课程中，你将通过探究科学家如何研究世界、物体如何运动以及不同形式的能量与物质如何活动，来构建扎实的基础。本文梳理了你需要掌握的所有核心知识点，从测量与力到电路与太空，帮助你自信地复习备考。
1. Scientific Inquiry | 科学探究
Science begins with curiosity. When designing an experiment, we identify variables: the independent variable is the one you change, the dependent variable is what you measure, and control variables are kept the same to make a fair test.
科学始于好奇。在设计实验时，我们要确定变量：自变量是你改变的变量，因变量是你测量的变量，控制变量则保持不变以确保公平测试。
A clear prediction or hypothesis tells others what you think will happen and why. You collect results in a table, then plot a graph to spot patterns. Always label axes with units and write a conclusion that explains your findings using scientific ideas.
清晰的预测或假设能告诉别人你认为会发生什么及其原因。你将结果收集在表格中，再绘制图表寻找规律。坐标轴要注明单位，并写出用科学原理解释发现的结论。
Safety is vital in the lab: listen to your teacher, wear goggles when needed, and never taste chemicals. Understanding hazards helps you work responsibly.
实验室安全至关重要：听从老师指导，必要时佩戴护目镜，切勿品尝化学药品。了解危险源能帮助你负责任地操作。
2. Measurements and Units | 测量与单位
Physicists use standard SI units: length in metres (m), mass in kilograms (kg), time in seconds (s), and temperature in kelvin (K), though we often use degrees Celsius (°C). Small lengths use centimetres (cm) or millimetres (mm); mass often measured in grams (g).
物理学家使用国际单位制：长度用米 (m)，质量用千克 (kg)，时间用秒 (s)，温度用开尔文 (K)，但我们常用摄氏度 (°C)。小长度用厘米 (cm) 或毫米 (mm)；质量常用克 (g)。
Use a ruler correctly, with your eye directly above the mark to avoid parallax error. A measuring cylinder gives volume in millilitres (ml) or cm³; always read the bottom of the meniscus at eye level. A stopwatch measures time, and a thermometer measures temperature.
正确使用直尺，眼睛正对刻度以避免视差。量筒以毫升 (ml) 或 cm³ 给出体积；始终在视线水平处读取弯月面的底部。秒表测量时间，温度计测量温度。
Converting units is essential: 1 m = 100 cm, 1 cm = 10 mm, 1 kg = 1000 g, 1 litre = 1000 ml = 1000 cm³. Practice moving the decimal point forwards or backwards when changing between units.
单位换算至关重要：1 m = 100 cm，1 cm = 10 mm，1 kg = 1000 g，1 L = 1000 ml = 1000 cm³。更换单位时记得练习移动小数点。
3. Forces and Motion | 力与运动
A force is a push or a pull and is measured in newtons (N) using a force meter. Contact forces include friction and air resistance; non-contact forces include gravity, magnetism and static electricity.
力是推力或拉力，用牛顿 (N) 作单位，由测力计测量。接触力包括摩擦力和空气阻力；非接触力包括重力、磁力和静电。
The weight of an object is the force of gravity on its mass. On Earth, gravity pulls with about 10 N for every kilogram. So a 5 kg object has a weight of about 50 N.
物体的重量是重力作用在其质量上的力。地球上，每千克约受到 10 N 的重力。因此一个 5 kg 物体的重量约为 50 N。
Speed tells us how fast something moves. The equation is:
speed = distance ÷ time
速度告诉我们某物移动有多快。其公式为：
速度 = 距离 ÷ 时间
On a distance–time graph, a horizontal line means the object is stationary, and a straight sloping line means steady speed. Balanced forces keep an object still or moving at constant speed; unbalanced forces cause a change in speed or direction.
在距离-时间图上，水平线表示物体静止，倾斜直线表示匀速。平衡力使物体保持静止或匀速运动；不平衡力导致速度或方向的变化。
4. Energy | 能量
Energy is the ability to do work. It exists in many forms: kinetic (movement), gravitational potential (stored due to height), elastic, thermal, light, sound, electrical and chemical.
能量是做功的能力。它以多种形式存在：动能（运动）、重力势能（因高度储存）、弹性势能、热能、光能、声能、电能和化学能。
The law of conservation of energy says energy cannot be created or destroyed — it can only be transferred from one store to another or changed into a different form. In a lamp, electrical energy is transferred into light and heat.
能量守恒定律指出，能量不能被创造或消灭 — 它只能从一个储能体转移到另一个，或转变为不同形式。在灯泡中，电能转化为光和热。
Energy sources are either renewable or non-renewable. Fossil fuels (coal, oil, gas) are non-renewable and will run out. Solar, wind, tidal and hydroelectric power are renewable and less polluting.
能源分为可再生能源和不可再生能源。化石燃料（煤、石油、天然气）是不可再生的，终将耗尽。太阳能、风能、潮汐能和水力发电是可再生的，污染更小。
5. Particle Model of Matter | 物质的粒子模型
All matter is made up of tiny particles that are constantly moving. In solids, particles are packed tightly in a fixed pattern and can only vibrate. In liquids, particles are close together but can slide past each other. In gases, particles are far apart and move quickly in all directions.
所有物质都由不断运动的微小粒子构成。固体中，粒子紧密排列成固定图案，只能振动。液体中，粒子彼此靠近但可以相互滑动。气体中，粒子相距很远，向各个方向快速运动。
Changing state involves energy: melting and boiling require energy, while freezing and condensation release energy. Evaporation happens at any temperature from the surface of a liquid, but boiling occurs throughout the liquid at the boiling point.
状态变化涉及能量：熔化和沸腾需要能量，而凝固和凝结释放能量。蒸发可以在任何温度下从液体表面发生，但沸腾是在整个液体中达到沸点时发生。
Diffusion is the spreading of particles from a region of high concentration to low concentration. This happens fastest in gases, more slowly in liquids and extremely slowly in solids.
扩散是粒子从高浓度区域向低浓度区域的扩散。它在气体中最快，液体中较慢，固体中极慢。
6. Thermal Energy Transfer | 热传递
Thermal energy always flows from hotter objects to cooler objects. There are three methods of transfer: conduction, convection and radiation.
热能总是从较热的物体流向较冷的物体。传递方式有三种：传导、对流和辐射。
Conduction occurs mainly in solids. The heat is passed along by vibrating particles colliding with their neighbours. Metals are good conductors because of delocalised electrons; non-metals, wood and plastic are insulators.
传导主要发生在固体中。热量通过振动粒子与相邻粒子的碰撞传递。金属由于自由电子而成为良导体；非金属、木材和塑料是绝缘体。
Convection occurs in liquids and gases. When a fluid is heated, particles move faster and spread apart, so the warmer region becomes less dense and rises. Cooler, denser fluid sinks, setting up a convection current.
对流发生在液体和气体中。流体受热时，粒子运动加快、分散，较热的区域密度变小而上升。较冷、密度较大的流体下沉，形成对流。
Radiation is the transfer of energy by infrared waves. It does not need a medium and can travel through a vacuum, like the Sun’s heat reaching Earth. Shiny, light-coloured surfaces reflect radiation, while dark, matt surfaces absorb and emit it well.
辐射是通过红外波传递能量，不需要介质，可以在真空中传播，比如太阳的热量到达地球。光亮浅色表面反射辐射，而黑暗粗糙表面善于吸收和发射辐射。
7. Light and Colour | 光与颜色
Light travels in straight lines until it hits an obstacle, forming shadows. When light hits a smooth surface, it reflects following the law of reflection: the angle of incidence equals the angle of reflection (i = r).
光沿直线传播，遇到障碍物时形成阴影。当光射到光滑表面时，会根据反射定律发生反射：入射角等于反射角 (i = r)。
A plane mirror forms 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.
平面镜形成虚像，正立、与物体大小相同，并且看上去在镜后的距离与物体到镜面的距离相等。
Refraction occurs when light passes from one medium to another at an angle, changing speed and bending. A prism disperses white light into a spectrum of seven colours: red, orange, yellow, green, blue, indigo and violet.
折射发生在光斜向从一种介质进入另一种介质时，速度改变从而弯折。棱镜将白光色散成七色光谱：红、橙、黄、绿、蓝、靛、紫。
An opaque object appears the colour of the light it reflects; it absorbs other colours. A transparent filter lets through only its own colour, absorbing the rest. Mixing the three primary colours of light — red, green and blue — produces all other colours.
不透明物体呈现它反射的光的颜色，吸收其他颜色。透明滤镜只让自身颜色的光透过，吸收其余。混合光的三原色 — 红、绿、蓝 — 能产生所有其他颜色。
8. Sound | 声音
Sound is produced by vibrations. These vibrations cause the surrounding medium (solid, liquid or gas) to vibrate in a longitudinal wave. Sound cannot travel through a vacuum because there are no particles to carry the vibration.
声音由振动产生。这些振动使周围介质（固体、液体或气体）以纵波的形式振动。声音不能在真空中传播，因为没有粒子来传递振动。
The speed of sound varies: it is fastest in solids, slower in liquids and slowest in gases. In air, sound travels at about 340 m/s.
声音的速度各异：在固体中最快，液体中较慢，气体中最慢。在空气中，声音传播速度约为 340 m/s。
Pitch is determined by the frequency of the sound wave, measured in hertz (Hz). A higher frequency gives a higher pitch. Loudness depends on the amplitude of the wave: a bigger amplitude makes a louder sound.
音高由声波的频率决定，以赫兹 (Hz) 为单位。频率越高，音高越高。响度取决于波的振幅：振幅越大，声音越响。
The human ear can detect frequencies roughly from 20 Hz to 20,000 Hz. Frequencies above this range are called ultrasound. Echoes are reflections of sound off hard surfaces.
人耳能检测到的频率范围大约为 20 Hz 至 20,000 Hz。高于此范围的频率称为超声波。回声是声音从坚硬表面反射回来的现象。
9. Basics of Electricity | 电路基础
An electric circuit needs a complete loop so current can flow. Electric current is a flow of charge, measured in amperes (A). Voltage is the ‘push’ that drives the current, measured in volts (V).
电路需要完整的回路以便电流流通。电流是电荷的流动，单位为安培 (A)。电压是驱动电流的“推力”，单位为伏特 (V)。
In a series circuit, there is only one path for current. The current is the same everywhere, but the voltage is shared between components. If one bulb breaks, the whole circuit stops working.
在串联电路中，电流只有一条通路。各处电流相同，但电压在各元件间分配。如果一只灯泡损坏，整个电路停止工作。
In a parallel circuit, there are multiple paths. The current is split between the branches, but each component gets the full battery voltage. A break in one branch does not stop the others.
在并联电路中，有多条通路。电流在各支路间分配，但每个元件都获得电池的完整电压。一条支路断开不影响其他支路。
You must recognise standard symbols: cell, battery, lamp, switch (open and closed), ammeter, voltmeter and resistor. Conductors, like metals, allow current to flow easily; insulators, such as plastic and rubber, do not.
你需要识别标准符号：电池、电池组、灯泡、开关（断开和闭合）、电流表、电压表和电阻器。导体（如金属）让电流轻易通过；绝缘体（如塑料和橡胶）则不行。
10. Magnetism | 磁学
A magnet has a north pole and a south pole. Like poles repel each other; unlike poles attract. The force is strongest at the poles, where the magnetic field is most concentrated.
磁体有北极和南极。同名磁极相互排斥，异名磁极相互吸引。在磁极处磁力最强，磁场也最集中。
A magnetic field is the region around a magnet where it can attract magnetic materials. Field lines point from north to south. The closer the lines, the stronger the field. Iron, nickel and cobalt are magnetic materials.
磁场是磁体周围能够吸引磁性材料的区域。磁感线从北极指向南极。线条越密，磁场越强。铁、镍、钴是磁性材料。
The Earth behaves like a giant magnet, with its magnetic north pole near the geographic south pole. A compass needle is a small bar magnet that aligns with the Earth’s field, pointing north.
地球如同一个巨大的磁体，其磁北极靠近地理南极。指南针的指针是一个小条形磁体，与地球磁场对齐，指向北方。
An electromagnet is made by winding a coil of wire around an iron core. When a current flows, it becomes magnetic; switching off the current removes the magnetism. Electromagnets are used in scrapyard cranes and doorbells.
电磁铁由绕在铁芯上的线圈制成。当电流通过时，它就带有磁性；切断电流，磁性消失。电磁铁用于废品场起重机和电铃中。
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