📚 SQA National 5 Physics: Core Knowledge Review | SQA National 5 物理：核心知识点梳理
Welcome to your essential recap of SQA National 5 Physics. This article brings together the key concepts, definitions and equations you must know for your final examination. Whether you are revising dynamics, waves or electricity, you will find clear explanations paired in English and Chinese to strengthen your understanding. Let's begin the journey through the core topics.
欢迎来到 SQA National 5 物理的核心知识点回顾。本文汇总了期末考试必须掌握的关键概念、定义和公式。无论你正在复习动力学、波动还是电学，都能在这里找到中英对照的清晰讲解，帮助你加深理解。让我们一起梳理这些核心主题。
1. Scalars and Vectors | 标量与矢量
Scalars are physical quantities that have magnitude only, such as speed, distance, mass, time and energy. When you describe an object moving at 5 m/s without stating its direction, you are giving a scalar quantity.
标量是只有大小的物理量，例如速率、路程、质量、时间和能量。当你描述一个物体以 5 m/s 运动而不指明方向时，你给出的就是一个标量。
Vectors have both magnitude and direction. Displacement, velocity, acceleration and force are vectors. A vector quantity can be represented by an arrow; the length shows the magnitude and the arrowhead indicates the direction. Adding vectors requires considering their directions, not just their magnitudes.
矢量既有大小又有方向。位移、速度、加速度和力都是矢量。矢量可以用箭头表示，长度代表大小，箭头指向代表方向。矢量的相加必须考虑方向，不能只简单地加和大小。
2. Speed, Velocity and Acceleration | 速度、速率与加速度
), a vector. Average speed is total distance over total time. Instantaneous speed is the speed at a particular instant.
速率是单位时间内通过的路程 (v = d / t)，是标量。速度是单位时间内的位移 (v = s / t)，是矢量。平均速率是总路程除以总时间，瞬时速率是某一瞬间的速率。
tres per second squared (m/s²). If an object slows down, the acceleration is negative, sometimes called deceleration. A velocity-time graph gives acceleration as the gradient and displacement as the area under the graph.
加速度是速度的变化率：a = (v - u) / t，单位为米每二次方秒 (m/s²)。如果物体减速，加速度为负值，常称为减速度。速度‑时间图中，斜率代表加速度，图线下方的面积代表位移。
3. Newton's Laws | 牛顿定律
Newton's first law states that an object remains at rest or moves with constant velocity unless an unbalanced force acts on it. This explains why seatbelts are needed: a passenger continues moving forward when the car stops suddenly.
牛顿第一定律指出，除非受到非平衡力的作用，物体将保持静止或匀速直线运动状态。这解释了为何需要安全带：汽车突然停止时，乘客会由于惯性继续向前运动。
Newton' n newtons, mass in kg). A large force produces a large acceleration, but a larger mass reduces the acceleration for the same force.
牛顿第二定律将非平衡力、质量和加速度联系起来：F = m a（力以牛顿为单位，质量以千克为单位）。力越大加速度越大，但若质量较大，相同的力产生的加速度较小。
Newton's third law says that for every action force there is an equal and opposite reaction force. These forces act on different objects. When you push a wall, the wall pushes back on you with equal magnitude.
牛顿第三定律指出，每一个作用力都有一个大小相等、方向相反的反作用力，且作用在不同的物体上。当你推墙时，墙也以同样大小的力反推你。
4. Energy and Conservation | 能量与守恒
Energy cannot be created or destroyed, only transferred or transformed. The principle of conservation of energy applies to all processes. Common energy stores include kinetic, gravitational potential, chemical, thermal and nuclear.
能量不能被创造或消灭，只能被转移或转化。能量守恒定律适用于所有过程。常见的能量储存形式包括动能、重力势能、化学能、热能和核能。
F d, transferring energy. When friction is negligible, the loss in gravitational potential energy equals the gain in kinetic energy (e.g., a pendulum or roller coaster).
动能 Eₖ = ½ m v²。重力势能 Eₚ = m g h（h 为高度，地球表面 g ≈ 10 m/s²）。做功 W = F d 就是能量的转移。当摩擦力可忽略时，重力势能的减少等于动能的增加（例如摆锤或过山车）。
5. Specific Heat Capacity | 比热容
ic heat capacity (4180 J/kg°C), which is why it is used in central heating systems and helps moderate coastal climates.
比热容 c 是指将 1 kg 物质升高 1 °C 所需的能量。公式为 Eₕ = c m ΔT。水的比热容很高 (4180 J/kg°C)，因此常用于集中供暖系统，并有助于调节沿海气候。
In experiments, you can measure c using a joulemeter and thermometer. Heat loss to the surroundings is the main source of error, so insulation is important. The same principle explains why the sea warms up more slowly than land in summer.
实验中可用焦耳计和温度计测量比热容。热量散失到周围环境是主要误差来源，因此保温措施很重要。同样的原理也解释了为什么夏天海水升温比陆地慢。
6. Gas Laws and the Kinetic Model | 气体定律与分子运动模型
es colliding with the walls of a container. At constant temperature, p V = constant (Boyle's law).
分子运动模型将气体粒子描述为体积可忽略、不断运动的微小圆球。压强是粒子撞击容器壁产生的。温度不变时，p V = 常数（玻意耳定律）。
At constant volume, pressure is directly proportional to absolute temperature (p ∝ 3 °C) is the temperature at which particle kinetic energy is minimal and pressure would be zero.
体积不变时，压强与绝对温度成正比（p ∝ T，温度以开尔文为单位）。绝对零度 (0 K = -273 °C) 是粒子动能最低、理论上压强为零的温度。
vert Celsius to kelvin by adding 273. The kinetic model explains that raising temperature increases average particle speed, leading to more frequent and harder collisions.
理想气体状态方程将上述关系结合：p V / T = 常数。注意先将摄氏温度加 273 转换为开尔文。分子运动模型解释为：升高温度使粒子平均速率增大，导致更频繁、更有力的碰撞。
7. Space Physics: Big Bang and Redshift | 空间物理：大爆炸与红移
The Big Bang theory states that the universe began from an extremely hot, dense point around 13.8 billion years ago and has been expanding ever since. Evidence includes the cosmic microwave background radiation and the redshift of galaxies.
大爆炸理论认为，宇宙约在 138 亿年前从一个极热、极密的奇点诞生，并一直在膨胀。证据包括宇宙微波背景辐射和星系的光谱红移。
ter the galaxy recedes, the greater the redshift. This relationship is described by Hubble's law: v = H₀ d (v is recession velocity, d is distance, H₀ is the Hubble constant).
当遥远星系远离我们时，其发出的光波被拉长、波长向红端移动，这就是红移。星系退行速度越快，红移越大。哈勃定律描述了这一关系：v = H₀ d（v 为退行速度，d 为距离，H₀ 为哈勃常数）。
Redshift supports the expanding universe model. The discovery of cosmic microwave background radiation, a faint glow left over from the early universe, further validated the Big Bang theory.
红移支持了宇宙膨胀模型。宇宙微波背景辐射，即早期宇宙残留的微弱光辉，进一步验证了大爆炸理论。
8. Wave Properties | 波的性质
Waves transfer energy without transferring matter. In transverse waves (e.g., light, water waves) the particle vibration is perpendicular to the direction of energy transfer. In longitudinal waves (e.g., sound) the vibration is parallel.
波传播能量而不传播物质。横波（如光波、水波）中，介质粒子的振动方向与能量传播方向垂直。纵波（如声波）中，振动方向与传播方向平行。
/f. Amplitude is the maximum displacement from equilibrium and relates to the energy carried by the wave.
核心的波动方程为 v = f λ，其中 v 是波速 (m/s)，f 是频率 (Hz)，λ 是波长 (m)。周期 T = 1/f。振幅是偏离平衡位置的最大位移，与波所传递的能量有关。
Diffraction occurs when waves spread out after passing through a gap or around an obstacle. Greater diffraction happens when the gap width is similar to the wavelength. This explains why you can hear sound around a corner but not see light.
衍射是指波通过狭缝或绕过障碍物时扩散的现象。当缝宽与波长相近时，衍射更为明显。这解释了为什么声音能绕过墙角而光不能。
9. Electromagnetic Spectrum | 电磁波谱
requency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
电磁波谱是一组横波家族，在真空中均以光速 (3.0 × 10⁸ m/s) 传播。按频率递增、波长递减排序：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。
Each part has distinct uses and dangers. Radio waves carry TV and radio signals; microwaves are used for cooking and communications; infrared is used in thermal imaging and remote controls; visible light allows us to see; ultraviolet is used for sterilisation but can cause skin cancer; X-rays are used in medical imaging; gamma rays are used in cancer treatment but are highly ionising.
各波段有各自的用途和危害。无线电波传输电视和广播信号；微波用于烹饪和通信；红外线用于热成像和遥控；可见光让我们看见世界；紫外线用于杀菌但可能引起皮肤癌；X 射线用于医学影像；伽马射线用于癌症治疗，但电离能力极强。
10. Refraction and Lenses | 折射与透镜
, air to glass), it slows down and bends towards the normal. The refractive index n = sin θ₁ / sin θ₂ (where θ₁ is in air for a typical problem).
折射是波从一种介质进入另一种介质时，因速度变化而改变传播方向的现象。当光从光疏介质进入光密介质（如空气到玻璃）时，速率减慢，并靠近法线偏折。折射率 n = sin θ₁ / sin θ₂（通常情况下 θ₁ 为空气中的入射角）。
ula is 1/f = 1/u + 1/v, where u is object distance and v is image distance. In a ray diagram, rays parallel to the principal axis pass through the focal point after the lens.
凸透镜使光线会聚，凹透镜使光线发散。透镜焦度 P = 1/f（f 以米为单位，P 的单位是屈光度）。薄透镜公式为 1/f = 1/u + 1/v，u 是物距，v 是像距。在光路图中，平行于主光轴的光线经透镜后通过焦点。
11. Nuclear Radiation | 核辐射
Nuclear radiation comes from unstable atomic nuclei. There are three main types: alpha (α), beta (β) and gamma (γ). Alpha particles are helium nuclei (2 protons + 2 neutrons), highly ionising but stopped by paper or a few cm of air. Beta particles are fast electrons, moderately ionising, stopped by a few mm of aluminium. Gamma rays are electromagnetic waves, weakly ionising, stopped by thick lead or concrete.
核辐射来源于不稳定的原子核。主要分三种：α（阿尔法）、β（贝塔）和 γ（伽马）。α 粒子是氦核（2 个质子 + 2 个中子），电离能力最强，但能被纸张或几厘米空气阻挡。β 粒子是高速电子，电离能力中等，可被几毫米铝板阻挡。γ 射线是电磁波，电离能力最弱，需用厚铅板或混凝土阻挡。
fe is the time for half of the nuclei in a sample to decay. It is used in radioactive dating and medical tracers. Background radiation comes from rocks, cosmic rays, food and medical procedures.
放射性活度的单位是贝克勒尔 (Bq)，1 Bq = 每秒 1 次衰变。半衰期是指样品中一半的原子核发生衰变所需的时间，应用于放射性测年和医用示踪剂。背景辐射来源于岩石、宇宙射线、食物和医疗过程。
12. Electricity: Circuits, Ohm's Law and Power | 电学：电路、欧姆定律和功率
Resistance R (ohms, Ω) measures how much a component resists current flow: R = V / I (Ohm's law).
电流 I（安培）是电荷的流动，1 安培等于每秒 1 库仑。电压 V（伏特）是单位电荷转移的能量。电阻 R（欧姆，Ω）衡量元件对电流的阻碍作用：R = V / I（欧姆定律）。
is the same everywhere, total voltage is shared, and total resistance R₍total₎ = R₁ + R₂ + … branch, current splits, and the reciprocal total resistance is 1/R₍total₎ = 1/R₁ + 1/R₂ + … .
在串联电路中，电流处处相等，总电压按电阻分配，总电阻 R₍总₎ = R₁ + R₂ + … 。在并联电路中，各支路电压相等，总电流等于各支路电流之和，总电阻的倒数满足 1/R₍总₎ = 1/R₁ + 1/R₂ + … 。
he practical unit of electrical energy is the kilowatt-hour (kWh). Fuses and circuit breakers protect circuits from excessive current.
电功率 P = I V，也可表示为 P = I² R 和 P = V² / R。电能 E = P t。实际中常用千瓦时 (kWh) 作为电能单位。保险丝和断路器用于防止电流过大。
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