📚 Cambridge Lower Secondary Science Workbook 9: Key Topics & Study Guide | 剑桥初中科学练习册9：核心考点与学习指南
Welcome to our revision guide for the Cambridge Lower Secondary Science Workbook 9. This workbook supports learners in mastering essential scientific concepts across biology, chemistry and physics, while also building valuable enquiry skills. With its digital access resources, you can benefit from interactive tasks, video clips and self-assessment activities. In this article we summarise the core topics you will encounter, providing clear explanations in both English and Chinese to help you strengthen your understanding and perform confidently in assessments.
欢迎阅读剑桥初中科学练习册9的复习指南。该练习册旨在帮助学生掌握生物、化学和物理领域的核心科学概念，并培养探究技能。通过数字访问，你可以使用互动任务、视频片段和自我评估活动。本文总结了你会遇到的各大核心主题，以中英双语提供清晰解说，帮助你巩固理解、自信应考。
1. Forces and Motion | 力与运动
Forces are pushes or pulls that can change the speed, direction or shape of an object. The unit of force is the newton (N). When the forces on an object are balanced, it remains stationary or moves with constant velocity. Unbalanced forces produce acceleration, described by Newton's second law. The relationship is:
F = m × a
where F is resultant force (N), m is mass (kg) and a is acceleration (m/s²). In Workbook 9 you will interpret force diagrams and calculate resultant forces from 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)。当物体受力平衡时，它保持静止或匀速直线运动。非平衡力产生加速度，由牛顿第二定律描述。关系式为 F = m × a，其中 F 是合力(N)，m 是质量(kg)，a 是加速度(m/s²)。在练习册9中，你将分析受力示意图，并根据隔离体图计算合力。
Motion can be represented using distance–time and speed–time graphs. The gradient of a distance– ph equals speed; a horizontal line indicates the object is at rest. The area under a speed– + a t is commonly applied, where u is initial velocity, v is final velocity and t is time.
v = u + a t
掌握距离-时间图和速度-时间图的解读至关重要。距离-时间图的斜率代表速度；水平线表示物体静止。速度-时间图下方的面积等于移动的距离。对于匀加速运动，常用 v = u + a t 方程，其中 u 为初速度，v 为末速度，t 为时间。
2. Energy Resources and Transfers | 能量资源与传递
otential, thermal, chemical, electrical and nuclear. Energy cannot be created or destroyed — sfer: P = W / t, in watts (W). Workbook 9 includes scenarios where you calculate work done and power in simple machines.
能量有多种形式：动能、重力势能、热能、化学能、电能和核能。能量不能凭空产生或消失——转移过程中总量守恒。力使物体移动所做的功 W = F × d，单位为焦耳(J)。功率是能量转移的速率：P = W / t，单位为瓦特(W)。练习册9中你会遇到计算简单机械中功和功率的情景。
Renewable energy resources include solar, wind, wave, hydroelectric, geothermal and biomass. Non‑renewable resources are fossil fuels (coal, oil, natural gas) and nuclear fuels. Understanding how each resource generates electricity and the environmental impacts is a key focus. You will also compare energy transfers by conduction, convection and radiation, using the particle model to explain thermal conduction in solids.
可再生能源包括太阳能、风能、波浪能、水电、地热和生物质能。不可再生能源指化石燃料（煤炭、石油、天然气）和核燃料。掌握每种能源如何发电及其环境影响是重点。你还将比较传导、对流和辐射的能量传递方式，并运用粒子模型解释固体中的热传导。
3. Waves: Sound and Light | 波：声与光
Waves transfer energy without transferring matter. Transverse waves, such as light and water ripples, have oscillations perpendicular to the wave direction. Longitudinal waves, such as sound, have oscillations parallel to the direction. The wave equation links speed, frequency and wavelength:
v = f × λ
where v is wave speed (m/s), f is frequency (Hz) and λ is wavelength (m). You will practise measuring wave properties and using this equation in Workbook 9.
波传递能量而不传递物质。横波（例如光波和水波）的振动方向与传播方向垂直，纵波（如声波）的振动方向与传播方向平行。波速方程联系波速、频率和波长：v = f × λ，其中 v 为波速(m/s)，f 为频率(Hz)，λ 为波长(m)。你将在练习册9中练习测量波的属性并运用该方程。
Sound travels fastest in solids, slower in liquids and slowest in gases, because particles are closer together in solids and can pass on vibrations more efficiently. Light waves can be reflected, refracted and absorbed. The law of reflection states that the angle of incidence equals the angle of reflection. Refraction occurs when light passes from one transparent medium to another, changing speed and direction. The electromagnetic spectrum organises waves from radio waves to gamma rays, all travelling at the same speed in a vacuum.
声音在固体中最快、液体次之、气体中最慢，这是因为固体中粒子更紧密，能更有效地传递振动。光波可以被反射、折射和吸收。反射定律指出入射角等于反射角。当光从一种透明介质进入另一种时会发生折射，速度和方向均改变。电磁波谱按频率排列从无线电波到伽马射线，所有电磁波在真空中速度相同。
4. Electricity and Magnetism | 电与
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