📚 Year 7 Cambridge Physics: Core Knowledge Points | Year 7 Cambridge 物理核心知识点梳理
This article summarises the essential physics topics for Year 7 Cambridge Lower Secondary Science, covering forces, energy, sound, light, electricity, magnetism and Earth in space. Each key point is explained clearly to help you build a solid foundation.
本文梳理了 Year 7 剑桥初中科学物理部分的核心知识点，涵盖力、能量、声音、光、电、磁以及地球与太空。每个要点均清晰解释，帮助你打下扎实的基础。
1. Forces – Pushes and Pulls | 力 – 推与拉
Forces are pushes or pulls that can change the shape, speed or direction of an object. They are measured in newtons (N).
力是推或拉，可以改变物体的形状、速度或方向。力的单位是牛顿 (N)。
Contact forces require objects to touch, such as friction, tension and air resistance. Non-contact forces act over a distance, like gravity and magnetism.
接触力需要物体相互接触，例如摩擦力、拉力和空气阻力。非接触力可以隔空作用，如重力和磁力。
Balanced forces result in no change in motion; unbalanced forces cause an object to start moving, speed up, slow down or change direction.
平衡力不改变物体的运动状态；不平衡力会使物体开始运动、加速、减速或改变方向。
2. Measuring Forces and Friction | 力的测量与摩擦力
Forces are measured using a force meter (spring balance). The reading on the scale indicates the size of the force in newtons.
力用弹簧测力计测量。刻度上的读数表示力的大小，单位是牛顿。
Friction is a force that opposes motion between two surfaces in contact. It can be reduced by using lubricants, wheels or streamlining.
摩擦力是阻碍两个接触表面相对运动的力。可以通过使用润滑剂、轮子或流线型设计来减小摩擦。
Friction often produces heat and can wear away materials. However, it is useful for walking, braking and gripping objects.
摩擦经常产生热量并磨损材料。然而，它对行走、刹车和抓取物体必不可少。
3. Gravity, Mass and Weight | 重力、质量与重量
Gravity is a non-contact force that pulls objects towards the centre of the Earth (or any other massive body). Weight is the force due to gravity acting on a mass.
重力是一种非接触力，将物体拉向地心（或其他大质量物体）。重量是作用在质量上的重力。
weight (N) = mass (kg) × gravitational field strength g (N/kg)
重量 (牛顿) = 质量 (千克) × 引力场强度 g (牛顿/千克)。在地球表面，g 约为 9.8 N/kg，通常近似取 10 N/kg。
Mass is the amount of matter in an object and is measured in kilograms (kg). It does not change with location. Weight, however, depends on the strength of gravity and can be different on the Moon.
质量是物体所含物质的多少，单位为千克 (kg)，不随位置变化。重量则取决于重力强度，在月球上会不同。
4. Energy – Stores and Transfers | 能量 – 储存与转移
Energy is a conserved quantity that can be stored in different ways and transferred between stores. It is measured in joules (J).
能量是守恒量，能以不同方式储存并在不同能量库间转移。能量的单位是焦耳 (J)。
Energy stores include kinetic (moving), gravitational potential (height), elastic potential (stretched or compressed), thermal (internal), chemical (food, fuels) and nuclear.
能量储存包括动能、重力势能、弹性势能、热能（内能）、化学能（食物、燃料）以及核能。
Energy can be transferred by forces (mechanical work), electric currents, heating, light and sound waves. In transfers, some energy is often dissipated as thermal energy.
能量可以通过力做功、电流、加热、光波和声波进行转移。转移过程中，部分能量常常耗散为热能。
5. Sound and Vibrations | 声音与振动
Sound is produced by vibrating objects. These vibrations travel as longitudinal waves through a medium (solid, liquid or gas).
声音由物体振动产生。这些振动以纵波的形式通过介质（固体、液体或气体）传播。
Sound cannot travel through a vacuum because there are no particles to transmit the vibrations. This is why space is silent.
声音不能在真空中传播，因为没有粒子传递振动。这就是太空中寂静无声的原因。
The louder the sound, the larger the amplitude of the wave. The higher the pitch, the higher the frequency (number of vibrations per second).
声音越响，振幅越大。音调越高，频率（每秒振动次数）越高。
6. Light Travels in Straight Lines | 光的直线传播
Light travels in straight lines. This explains the formation of sharp shadows and why we cannot see around corners.
光沿直线传播。这解释了清晰影子的形成以及为何我们无法看到拐角后的物体。
imately 300 000 kilometres per second (3 × 10⁸ m/s). Light travels much faster than sound.
光在真空中的速度约为每秒 30 万千米 (3 × 10⁸ m/s)。光速远大于声速。
When light hits an opaque object, a shadow is formed on the opposite side. The size and shape of a shadow depend on the distance and angle of the light source.
当光照到不透明物体上时，在背光面形成影子。影子的大小和形状取决于光源的距离和角度。
7. Reflection and Seeing | 反射与视觉
We see objects because light from a source reflects off them and enters our eyes. The angle of incidence equals the angle of reflection.
我们看见物体是因为光源发出的光从物体反射进入眼睛。入射角等于反射角。
A plane mirror produces a virtual, upright image that is laterally inverted (left and right appear swapped). The image appears the same distance behind the mirror as the object is in front.
平面镜产生正立、虚像，且左右颠倒。像到镜面的距离等于物体到镜面的距离。
Smooth, shiny surfaces produce clear reflections (specular reflection), while rough surfaces scatter light in many directions (diffuse reflection).
光滑闪亮的表面产生清晰的反射（镜面反射），而粗糙表面将光向各个方向散射（漫反射）。
8. Colours of Light | 光的颜色
White light is made of a spectrum of colours: red, orange, yellow, green, blue, indigo and violet. This can be shown by passing light through a glass prism.
白光由一系列颜色组成：红、橙、黄、绿、蓝、靛、紫。让光通过玻璃棱镜可以展示这一光谱。
The splitting of white light into colours is called dispersion. Rainbows are natural examples of dispersion by water droplets.
白光分解为各种颜色的现象叫做色散。彩虹就是由水滴引起的天然色散。
Objects appear coloured because they reflect certain colours and absorb others. For example, a red apple reflects red light and absorbs the other colours.
物体呈现颜色是因为它们反射某些颜色的光并吸收其他颜色。例如，红苹果反射红光，吸收其他颜色的光。
9. Electric Circuits | 电路
An electric circuit is a complete loop that allows electric current to flow. Current is the flow of electric charge and is measured in amperes (A).
电路是允许电流流动的闭合回路。电流是电荷的流动，单位是安培 (A)。
A simple circuit requires a cell (or battery), connecting wires and a component such as a lamp or buzzer. Adding more cells increases the current; adding more bulbs in series often reduces brightness.
简单电路需要电池、导线和用电器（如灯泡或蜂鸣器）。增加电池会增大电流；串联更多灯泡通常会降低亮度。
Conductors (like metals) allow electricity to flow easily, while insulators (like rubber, plastic) block the flow. A switch acts as an intentional break in a circuit.
导体（如金属）容易让电流通过，而绝缘体（如橡胶、塑料）阻碍电流。开关在电路中起有意的断开作用。
10. Magnetism | 磁性
A magnet has two poles – north (N) and south (S). Like poles repel, unlike poles attract.
磁铁有两个磁极——北极 (N) 和南极 (S)。同极相斥，异极相吸。
The space around a magnet where it can exert a force is the magnetic field. Field lines go from north to south outside the magnet.
磁铁周围能施加力的空间称为磁场。磁感线在磁铁外部从北极指向南极。
The Earth itself acts like a giant magnet with a magnetic field. A compass needle aligns with this field, pointing roughly towards the geographic North Pole.
地球本身就像一个拥有磁场的巨大磁体。指南针的指针与地磁场对齐，大致指向地理北极。
11. Earth and Space | 地球与太空
The Earth rotates on its axis once every 24 hours, causing day and night. The side facing the Sun experiences daylight.
地球每 24 小时绕地轴自转一周，形成昼夜。面向太阳的一面为白昼。
The Earth orbits the Sun once every 365 ¼ days, which gives us a year. The tilt of the Earth's axis causes seasons as different hemispheres receive varying amounts of sunlight.
地球每 365 ¼ 天绕太阳公转一周，为一年。地轴的倾斜导致不同半球接收的太阳光量变化，形成四季。
The Solar System consists of the Sun, eight planets and other objects like moons and asteroids. The order of planets from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
太阳系由太阳、八大行星以及卫星、小行星等天体组成。行星离太阳由近及远的顺序是：水星、金星、地球、火星、木星、土星、天王星、海王星。
The force of gravity keeps planets in orbit around the Sun and moons in orbit around planets.
重力使行星围绕太阳运转，并使卫星围绕行星运转。
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