📚 Year 9 SQA Physics: Core Knowledge Overview | Year 9 SQA 物理：核心知识点梳理
This article provides a comprehensive outline of the core physics topics that Year 9 students encounter in the SQA science framework. Mastering these fundamental ideas will prepare you well for National 4 and National 5 Physics, covering forces, energy, electricity, waves, and much more.
本文系统梳理了 SQA 课程体系中 Year 9 物理的核心主题。掌握这些基本概念，将为后续 National 4 和 National 5 物理的学习打下扎实基础，内容涵盖力、能量、电路、波等关键模块。
1. Forces and Their Effects | 力及其效应
A force is a push or a pull that can change an object's shape, speed, or direction of motion. Forces are vector quantities, so they have both magnitude and direction, and they are measured in newtons (N).
力是一种推或拉的作用，能够改变物体的形状、速度或运动方向。力是矢量，既有大小又有方向，其单位是牛顿（N）。
We often represent forces using arrows in free-body diagrams. Contact forces require objects to be touching, whereas non-contact forces act at a distance.
我们通常用自由体图中的箭头来表示力。接触力需要物体相互接触才能产生，而非接触力可以在一定距离外产生作用。
| Contact forces | Non-contact forces |
| Friction, tension, normal reaction | Gravity, magnetic, electrostatic |
Balanced forces cancel each other out, so an object remains at rest or moves with constant velocity. Unbalanced forces produce a resultant force, causing the object to accelerate, decelerate, or change direction.
平衡力相互抵消，使得物体保持静止或匀速直线运动。不平衡力会产生合力，导致物体加速、减速或改变运动方向。
Hooke' ceeded. It is written as F = k × x, where k is the spring constant and x is the extension.
胡克定律适用于许多弹簧：在弹性限度内，弹簧的伸长量与施加的力成正比。公式为 F = k × x，其中 k 是弹簧常数，x 是伸长量。
2. Speed, Velocity and Acceleration | 速率、速度与加速度
Speed is a scalar quantity that tells us how fast an object is moving, while velocity is a vector – it describes both speed and direction. Acceleration measures how quickly velocity changes.
速率是标量，表示物体运动的快慢；而速度是矢量，不仅描述快慢，还包含运动方向。加速度衡量速度变化的快慢。
speed = distance ÷ time v = d ÷ t
acceleration = change in velocity ÷ time a = (v - u) ÷ t
A distance–time graph shows how far an object has travelled. A straight, sloping line indicates constant speed, while a horizontal line means the object is stationary. The gradient of a distance–time graph gives the speed.
距离-时间图像表示物体运动的距离。倾斜直线表示匀速运动，水平线则表示物体静止。距离-时间图像的斜率代表速率。
On a speed–time graph, a horizontal line represents constant speed, an upward slope shows acceleration, and a downward slope shows deceleration. The area under a speed–time graph equals the distance travelled.
在速度-时间图像中，水平线表示匀速，向上倾斜表示加速，向下倾斜表示减速。速度-时间图像下的面积等于运动的距离。
3. Mass, Weight and Gravity | 质量、重量与重力
Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity pulling on that mass, measured in newtons (N). The two are related but not the same.
质量是物体所含物质的多少，单位是千克（kg）。重量是作用在物体上的重力，单位是牛顿（N）。两者相关但并不相同。
W = m × g
On Earth, the gravitational field strength g is approximately 9.8 N/kg. This means a 1 kg mass experiences a weight of 9.8 N. Your weight would be different on the Moon because g is lower there.
在地球上，重力场强度 g 约等于 9.8 N/kg，即质量为 1 kg 的物体受到 9.8 N 的重力。在月球上，由于 g 较小，你的重量会变轻。
4. Energy Types and Transfers | 能量类型与转化
Energy exists in many forms: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, electrical, light, and sound. Energy cannot be created or destroyed – only transferred or converted from one form to another.
能量有多种形式：动能、重力势能、弹性势能、热能、化学能、核能、电能、光能和声能。能量既不能被创造，也不能被消灭，只能在不同形式之间转移或转化。
Kinetic energy depends on mass and speed. Gravitational potential energy depends on mass, gravitational field strength, and height.
动能取决于物体的质量和速度。重力势能取决于质量、重力场强度和高度。
Eₖ = ½ m v² Eₚ = m g h
lculated by multiplying force by distance moved in the direction of the force (W = F × d).
当力使物体移动时，就做了功，所做的功等于传递的能量。功的大小等于力乘以物体在力的方向上移动的距离（W = F × d）。
Energy efficiency compares the useful output energy to the total input energy. It is often expressed as a percentage and can never be greater than 100%.
能量效率比较有用输出能量与总输入能量。通常用百分数表示，并且永远不可能超过 100%。
5. Electricity: Current, Voltage and Resistance | 电流、电压与电阻
Electric current is the flow of electric charge and is measured in amperes (A). In a circuit, current only flows when there is a complete path and a source of voltage.
电流是电荷的流动，单位是安培（A）。在电路中，只有形成闭合回路并且存在电压源时，才会有电流通过。
Voltage (potential difference) measures the energy transferred per unit charge and is measured in volts (V). Resistance opposes the flow of current and is measured in ohms (Ω).
电压（电势差）衡量每单位电荷所传递的能量，单位是伏特（V）。电阻阻碍电流的流动，单位是欧姆（Ω）。
V = I × R
Ohm's law states that for many conductors, the current is directly proportional to the voltage across them, provided the temperature remains constant.
欧姆定律指出，对于许多导体，在温度保持不变的条件下，通过导体的电流与导体两端的电压成正比。
In a series circuit, the current is the same everywhere, but the voltage is shared across components. In a parallel circuit, the voltage across each branch is the same, while the current splits between branches.
在串联电路中，各处电流相等，但电压由各元件分担。在并联电路中，各支路两端的电压相等，而总电流被分成多路。
voltage (P = I × V). The total energy transferred is power multiplied by time (E = P × t).
电功率表示能量传递的快慢，等于电流乘以电压（P = I × V）。传递的总能量等于功率乘以时间（E = P × t）。
6. Waves and Sound | 波及声音
Waves transfer energy from one place to another without transferring matter. Mechanical waves, like sound and water waves, need a medium to travel through, whereas electromagnetic waves do not.
波将能量从一处传递到另一处，而不传递物质。机械波（如声波和水波）需要介质才能传播，而电磁波则不需要。
There are two main types of waves: transverse waves, where the vibration is perpendicular to the direction of energy transfer (e.g., light, water ripples), and longitudinal waves, where the vibration is parallel (e.g., sound).
波主要分为两种：横波中介质振动方向与能量传递方向垂直（如光波、水波涟漪），纵波中振动方向与能量传递方向平行（如声波）。
Key wave properties include wavelength (λ), frequency (f), amplitude, and period. The wave speed equation links these quantities.
波的关键属性包括波长（λ）、频率（f）、振幅和周期。波速公式将这些量联系了起来。
v = f × λ
Sound waves are produced by vibrating objects and travel fastest in solids and slowest in gases. The pitch of a sound depends on its frequency, while the loudness depends on the amplitude.
声波由物体振动产生，在固体中传播最快，在气体中最慢。音调（音高）取决于频率，响度取决于振幅。
7. Light and the Electromagnetic Spectrum | 光与电磁波谱
e electromagnetic spectrum arranges all electromagnetic waves by wavelength and frequency.
光是横波，属于电磁波，能在真空中以大约 3×10⁸ m/s 的速度传播。电磁波谱将所有电磁波按波长和频率顺序排列。
| Radio waves | Microwaves | Infrared | Visible light | Ultraviolet | X-rays | Gamma rays |
Each type of electromagnetic radiation has practical uses: radio waves for communication, microwaves for cooking, infrared for thermal imaging, ultraviolet for sterilisation, X-rays for medical imaging, and gamma rays for cancer treatment.
每种电磁辐射都有实际应用：无线电波用于通信，微波用于烹饪，红外线用于热成像，紫外线用于消毒，X 射线用于医学成像，伽马射线用于癌症治疗。
The law of reflection states that the angle of incidence equals the angle of reflection. Refraction occurs when light changes speed as it passes from one medium to another, causing the ray to bend.
反射定律指出入射角等于反射角。当光从一种介质进入另一种介质时，速度发生变化，引起光线偏折，这就是折射。
8. Heat and Thermal Energy Transfer | 热与热能传递
Heat is the transfer of thermal energy from a hotter object to a cooler one. Temperature measures how hot an object is and is usually measured in degrees Celsius (°C) or kelvin (K).
热量是热能从较热物体传递到较冷物体的过程。温度衡量物体的冷热程度，通常用摄氏度（°C）或开尔文（K）表示。
Thermal energy can be transferred in three ways: conduction (mainly in solids), convection (in liquids and gases), and radiation (via infrared waves, does not require a medium).
热能的传递方式有三种：传导（主要在固体中），对流（在液体和气体中），以及辐射（通过红外波，无需介质）。
Materials that allow heat to pass through them easily are called conductors (e.g., metals), while insulators (e.g., plastic, wool) slow down heat transfer.
容易让热量通过的材料称为导体（如金属），而绝缘体（如塑料、羊毛）会减缓热传递。
nge. The relationship can be written as E = m c Δθ, where c is the specific heat capacity.
升高物体温度所需的热能取决于其质量、比热容和温度变化量。这一关系可表示为 E = m c Δθ，其中 c 是比热容。
9. Energy Resources and Sustainability | 能源与可持续发展
Energy resources are split into non-renewable sources (fossil fuels like coal, oil, natural gas, and nuclear fuels) and renewable sources (solar, wind, hydroelectric, wave, tidal, geothermal, and biomass).
能源可分为不可再生能源（化石燃料，如煤、石油、天然气，以及核燃料）和可再生能源（太阳能、风能、水力、波浪能、潮汐能、地热能和生物质能）。
Fossil fuels release carbon dioxide when burned, contributing to climate change, and they will eventually run out. Nuclear power produces radioactive waste that must be stored safely.
化石燃料燃烧会释放二氧化碳，加剧气候变化，并且终将枯竭。核能发电会产生必须安全存储的放射性废物。
Renewable energy sources are sustainable and have a much smaller carbon footprint, but they often depend on weather conditions and may require large land areas or specific locations.
可再生能源是可持续的，碳足迹小得多，但它们的利用往往依赖天气条件，并且可能需要大片土地或特定的地理环境。
Making energy choices involves balancing reliability, cost, environmental impact, and the need to reduce greenhouse gas emissions. A mix of energy sources is often used to ensure electricity supply meets demand.
能源决策需要在可靠性、成本、环境影响以及减少温室气体排放之间取得平衡。通常采用多种能源的组合，以确保电力供应满足需求。
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