Year 7 Cambridge Physics: Core Knowledge Review | Year 7 Cambridge 物理：核心知识点梳理

📚 Year 7 Cambridge Physics: Core Knowledge Review | Year 7 Cambridge 物理：核心知识点梳理

Welcome to your Year 7 Cambridge Physics journey! This article pulls together the essential knowledge you need, from understanding forces and motion to exploring energy, electricity, waves, the particle model and our solar system. Each section links key concepts with clear explanations, preparing you for assessments and sparking your curiosity about the physical world.

欢迎来到 Year 7 Cambridge 物理的学习之旅！本文梳理了从力与运动到能量、电学、波、粒子模型和太阳系的核心必备知识。每个部分都用清晰的解释串联关键概念，帮助你备考并激发对物理世界的好奇心。

1. What Is a Force? | 什么是力？

A force is simply a push or a pull that acts on an object. It can cause an object to start moving, speed up, slow down, change direction or change shape. Forces are measured in newtons (N).

力就是作用在物体上的推或拉。它能使物体开始运动、加速、减速、改变方向或变形。力的单位是 牛顿（N）。

There are two main types of forces: contact forces (such as friction, tension and normal reaction) that require objects to be touching, and non-contact forces (such as gravity, magnetism and electrostatic force) that act at a distance.

力主要分为两类：接触力（如摩擦力、拉力和支持力）需要物体相互接触；非接触力（如引力、磁力和静电力）则能在一定距离外产生作用。

When several forces act on an object, we can find the resultant force. If the forces are balanced, the object stays at rest or moves at a constant speed. If the forces are unbalanced, the object accelerates or decelerates.

当多个力作用于同一个物体时，我们可以求出合力。如果力平衡，物体将保持静止或匀速运动；如果力不平衡，物体会加速或减速。

2. Describing Motion | 描述运动

Motion can be described using speed, distance and time. Speed tells us how fast an object is moving. Average speed can be calculated with the equation:

运动可以用速度、距离和时间来描述。速度表示物体运动的快慢。平均速度可以用以下公式计算：

average speed = total distance ÷ total time

Distance is measured in metres (m) or kilometres (km), time in seconds (s) or hours (h), and speed often in metres per second (m/s) or kilometres per hour (km/h).

距离以米（m）或千米（km）为单位，时间以秒（s）或小时（h）为单位，速度通常用米每秒（m/s）或千米每小时（km/h）表示。

A distance–time graph shows the journey of an object. A straight, sloping line means the object is moving at a steady speed. A horizontal line means it is stationary. The steeper the line, the faster the motion.

距离–时间图 记录物体的行程。倾斜的直线表示物体匀速运动；水平线表示物体静止。线段越陡，运动速度越快。

Distance–time graphs help us calculate speed from the gradient (slope) of the line.
距离–时间图可以帮助我们通过线的斜率计算速度。

3. Gravity and Weight | 重力与重量

Mass is the amount of matter in an object, measured in kilograms (kg). It does not change wherever you are. Weight is the force of gravity acting on a mass, measured in newtons (N). Weight can change depending on the gravitational field strength.

质量是物体所含物质的多少，单位是千克（kg），不随位置改变。重量是作用在物体质量上的引力，单位是牛顿（N），会根据引力场强度而变化。

The relationship is given by:

两者的关系为：

weight = mass × gravitational field strength

W = m × g

On Earth, the gravitational field strength g ≈ 10 N/kg. This means a 1 kg mass has a weight of about 10 N. On the Moon, g is only about 1.6 N/kg, so you would weigh much less there.

地球上的引力场强度 g ≈ 10 N/kg，这意味着 1 kg 的质量约重 10 N。月球上的 g 仅约 1.6 N/kg，因此人在那里会轻得多。

4. Friction and Air Resistance | 摩擦力与空气阻力

Friction is a contact force that opposes motion between two surfaces. It can be useful (e.g., walking, braking) or unwanted (causing wear and wasting energy). Friction generates heat.

摩擦力 是阻碍两个表面间相对运动的接触力。它可能有用（如走路、刹车），也可能不受欢迎（造成磨损、浪费能量）。摩擦会产生热。

Air resistance (drag) is a type of friction that acts on objects moving through the air. It increases with speed and with the surface area of the object. Streamlined shapes reduce air resistance, allowing faster movement.

空气阻力（拖曳力）是物体在空气中运动时受到的摩擦力。它随速度和物体的横截面积增大而增大。流线型设计可以减少空气阻力，让运动更快。

When an object falls, air resistance increases until it balances the weight. At this point the resultant force is zero and the object falls at a constant terminal velocity.

物体下落时，空气阻力逐渐增大，直到与重量平衡。此时合力为零，物体以不变的 终端速度 下落。

5. Energy: Forms and Transfers | 能量：形式与转移

Energy is the ability to do work. It is measured in joules (J). Energy cannot be created or destroyed — it can only be transferred from one store to another or changed from one form to another. This is the principle of conservation of energy.

能量是做功的能力，单位是 焦耳（J）。能量既不能被创造也不能被消灭——它只能从一个储存库转移到另一个，或从一种形式转化为另一种形式。这就是 能量守恒定律。

Common energy stores (or forms) include:

常见的能量储存（或形式）包括：

Kinetic energy (movement)
动能（运动）
Gravitational potential energy (height)
重力势能（高度）
Thermal (heat) energy
热能
Light energy
光能
Sound energy
声能
Electrical energy
电能
Chemical energy (stored in food and fuels)
化学能（储存在食物和燃料中）

Energy transfers can be shown using simple energy flow diagrams. For example, a torch transfers chemical energy in a battery → electrical energy in wires → light + thermal energy in the bulb.

能量转移可以用简单的能量流程图表示。例如，手电筒：电池中的化学能 → 导线中的电能 → 灯泡产生的光能和热能。

6. Introduction to Electric Circuits | 电路入门

An electric circuit is a closed loop that allows electric current to flow. A basic circuit must have a source (such as a cell), a load (such as a bulb) and connecting wires. A switch can open or close the circuit.

电路是允许电流流动的闭合回路。基本电路必须包含电源（如电池）、用电器（如灯泡）和连接导线。开关可以断开或闭合电路。

Electric current is the flow of electric charge and is measured in amperes (amps, A). In a series circuit, current is the same everywhere. In a parallel circuit, current splits at junctions.

电流是电荷的流动，单位是 安培（A）。在串联电路中，各处电流相同；在并联电路中，电流在分支点分流。

Voltage (potential difference) is the ‘push’ that drives the current and is measured in volts (V). In a series circuit, voltage is shared between components. In a parallel circuit, each branch gets the full source voltage.

电压（电势差）是驱动电流的“推动力”，单位是 伏特（V）。串联电路中，各元件分担电压；并联电路中，每条支路都能获得完整的电源电压。

Components can be drawn using circuit symbols. Knowing common symbols for cells, bulbs, switches and buzzers is essential for reading and drawing circuit diagrams.

电路元件用电路符号表示。熟悉电池、灯泡、开关、蜂鸣器等常见符号对识读和绘制电路图至关重要。

7. The Particle Model of Matter | 物质的粒子模型

All substances are made of tiny, invisible particles. The particle model helps explain the properties of solids, liquids and gases and how they behave.

所有物质都由微小、不可见的粒子组成。粒子模型 有助于解释固体、液体和气体的性质及其行为。

In solids, particles are closely packed in a fixed arrangement, vibrating in place. This gives solids a definite shape and volume.

固体中，粒子紧密排列在固定位置，原地振动。这使得固体有固定的形状和体积。

In liquids, particles are still close but can slide past each other. Liquids have a definite volume but take the shape of their container.

液体中，粒子仍然靠近，但可以相互滑动。液体有固定的体积，却会随容器改变形状。

In gases, particles are far apart and move quickly in all directions. Gases have no fixed shape or volume and can be compressed easily.

气体中，粒子相距很远并向各个方向快速运动。气体既无固定形状也无固定体积，且容易被压缩。

Changes of state — melting, freezing, boiling, condensing — can be explained by changes in the energy of particles. Adding heat makes particles move faster or break free from fixed positions.

状态变化——熔化、凝固、沸腾、凝结——可以通过粒子能量的变化来解释。加热使粒子运动加快或挣脱固定位置。

8. Sound Waves | 声波

Sound is produced by vibrations. These vibrations travel through a medium (solid, liquid or gas) as a longitudinal wave. Sound cannot travel through a vacuum because there are no particles to pass the vibrations along.

声音由振动产生。这些振动以纵波的形式通过介质（固体、液体或气体）传播。声音在真空中无法传播，因为没有粒子来传递振动。

The frequency of a sound wave determines its pitch. A higher frequency gives a higher-pitched sound. Frequency is measured in hertz (Hz). Humans can typically hear sounds between 20 Hz and 20 000 Hz.

声波的频率决定音调高低。频率越高，音调越高。频率的单位是 赫兹（Hz）。人耳通常能听到 20 Hz 到 20 000 Hz 之间的声音。

The amplitude of a wave determines the loudness. A larger amplitude means a louder sound. Loudness is measured in decibels (dB), although Year 7 focuses on linking amplitude to energy.

波幅（振幅）决定响度。振幅越大，声音越响。响度以分贝（dB）为单位，但 Year 7 更关注振幅与能量的关联。

Sound travels faster in solids than in liquids, and faster in liquids than in gases, because particles are closer together.

声音在固体中传播速度比在液体中快，在液体中又比在气体中快，因为粒子排列更紧密。

9. Light and Optics | 光与光学

Light travels in straight lines at a speed of about 300 000 km/s in a vacuum. We see objects because light from a source reflects off them and enters our eyes.

光沿直线传播，在真空中的速度约为 300 000 km/s。我们能看到物体，是因为来自光源的光经物体反射后进入我们的眼睛。

Reflection occurs when light bounces off a surface. On a smooth surface like a plane mirror, the angle of incidence equals the angle of reflection, both measured from the normal at 90° to the mirror.

当光从表面反弹时发生反射。在平面镜等光滑表面上，入射角等于反射角，两者都从镜面的法线（90°线）量起。

In a plane mirror, the image is virtual, upright, laterally inverted (left appears right) and the same size as the object.

平面镜所成的像是虚像、正立、左右颠倒，且与物体大小相同。

Refraction is the bending of light when it passes from one transparent medium to another (e.g., from air to glass or water). This happens because light changes speed in different materials.

折射是光从一种透明介质进入另一种介质（如从空气进入玻璃或水）时的弯曲现象。这是因为光在不同材料中的速度不同。

White light can be split into a spectrum of colours (red, orange, yellow, green, blue, indigo, violet) by a prism. This process is called dispersion.

白光可以通过棱镜分解为彩色光谱（红、橙、黄、绿、蓝、靛、紫）。这个过程叫做色散。

10. Our Solar System | 我们的太阳系

The solar system consists of the Sun at the centre, with eight planets orbiting it: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Many planets have moons.

太阳系以太阳为中心，八大行星围绕它运行：水星、金星、地球、火星、木星、土星、天王星和海王星。许多行星都有卫星。

The Earth orbits the Sun once a year (about 365¼ days) and rotates on its axis once every 24 hours, causing day and night. The Moon orbits the Earth about every 28 days.

地球每年（约 365¼天）绕太阳公转一周，每 24 小时自转一周，形成昼夜。月球约每 28 天绕地球运行一周。

The seasons are not caused by varying distance from the Sun, but by the tilt of the Earth’s axis (about 23.5°). When a hemisphere is tilted towards the Sun, it experiences summer with longer days and higher temperatures.

季节并不是由日地距离变化引起的，而是因为 地轴倾斜（约 23.5°）。当一个半球倾向太阳时，那里就是夏季，昼长更长，气温更高。

Our solar system is just a tiny part of the Milky Way galaxy, which contains billions of stars. The Sun is our nearest star and the main source of energy for Earth.

太阳系只是包含数十亿颗恒星的银河系中的一小部分。太阳是离我们最近的恒星，也是地球能量的主要来源。

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Year 7 Cambridge Physics: Core Knowledge Review | Year 7 Cambridge 物理：核心知识点梳理