📚 Year 8 SQA Physics Formula & Theorem Quick Reference Handbook | SQA 物理公式定理速查手册
This quick reference handbook brings together all the essential formulas, key principles, and must-know theorems for Year 8 Physics under the Scottish Qualifications Authority (SQA) Science framework. Whether you are revising for an end-of-topic test or building foundations for future National qualifications, having a clear, bilingual summary saves time and boosts understanding. Each entry is presented in both English and Chinese to support EAL learners and deepen conceptual grasp through dual-language explanation.
这本速查手册汇集了 SQA 科学框架下 Year 8 物理所有核心公式、关键原理与必考定理。无论你是在准备单元测验，还是为未来的 National 资格证书打基础，清晰的双语总结都能节省时间并加深理解。每一条目均以中英双语呈现，既支持英语非母语学习者，也借助中文解释强化概念掌握。
1. Average Speed Formula | 平均速度公式
Average speed is defined as the total distance travelled divided by the total time taken. This relationship is fundamental when analysing motion in a straight line, and it gives a single value that describes the overall rate of movement, even if the object speeds up or slows down during the journey.
平均速度定义为总路程除以总时间。这一关系是分析直线运动的基础，即使物体在运动过程中加速或减速，它也能用一个数值描述整体的运动快慢。
average speed = total distance ÷ total time
v = d / t
The units often encountered are metres per second (m/s) when distance is in metres (m) and time is in seconds (s). In daily situations, kilometres per hour (km/h) may also appear, so remember to convert units consistently.
单位常用米/秒 (m/s)，此时距离用米 (m)、时间用秒 (s)。日常生活中也可能出现千米/时 (km/h)，记得统一换算单位。
2. Instantaneous Speed and Distance–Time Graphs | 瞬时速度与距离–时间图像
While average speed gives a general picture, instantaneous speed is the speed at a particular moment. On a distance–time graph, a straight sloped line represents constant speed, and the gradient of the line equals the speed.
平均速度给出总体情况，而瞬时速度是某一特定时刻的速度。在距离–时间图像中，一条倾斜的直线代表匀速运动，直线的斜率等于速度。
A steeper gradient indicates a higher speed, while a horizontal line means the object is stationary. If the line curves, the speed is changing, and the gradient at any point can be found by drawing a tangent.
斜率越陡表示速度越快，水平线则代表物体静止。如果线条弯曲，意味着速度在变化，可通过作切线求出任一点的瞬时速度。
- Gradient = speed (m/s)
- 斜率 = 速度 (m/s)
3. Acceleration and Velocity Change | 加速度与速度变化
Acceleration is the rate at which an object changes its velocity. In Year 8, we focus on uniform acceleration, where the velocity changes by the same amount each second.
加速度是物体速度变化的快慢。Year 8 阶段我们主要研究匀加速运动，即每秒速度变化量相同。
acceleration = change in speed ÷ time taken
a = (v − u) / t
Here, u is the initial speed, v is the final speed, and t is the time for the change. The SI unit is metres per second squared (m/s²).
其中 u 为初速度，v 为末速度，t 为变化时间。国际单位是米/秒² (m/s²)。
Remember: if an object slows down, the final speed is smaller than the initial speed, so acceleration becomes negative – this is sometimes called deceleration.
注意：物体减速时末速度小于初速度，加速度为负值——有时称为减速度。
4. Speed–Time Graphs and Area Under the Line | 速度–时间图像与线下面积
A speed–time graph shows how speed changes over time. The gradient of the line gives acceleration, while the area between the line and the time axis represents the distance travelled.
速度–时间图像展示速度随时间的变化。线的斜率给出加速度，而图线与时间轴之间的面积代表行驶的距离。
For a horizontal straight line, acceleration is zero and the speed is constant. For a slanted straight line, acceleration is constant. The area can often be calculated using simple shapes like rectangles and triangles.
水平直线表示加速度为零、速度恒定；倾斜直线表示加速度恒定。面积通常可用矩形或三角形等简单图形求解。
5. Forces: Resultant Force and Newton’s Second Law | 力：合力与牛顿第二定律
Forces are pushes or pulls measured in newtons (N). When several forces act on an object, we find the resultant force by adding them together, taking direction into account. Balanced forces produce no change in motion, while unbalanced forces cause acceleration.
力是推或拉，单位是牛顿 (N)。多个力作用在同一物体上时，需要考虑方向进行矢量求和，得到合力。平衡力不改变运动状态，不平衡力会产生加速度。
F = m × a
This famous equation states that resultant force (F) equals mass (m) multiplied by acceleration (a). If mass is in kilograms (kg) and acceleration in m/s², force comes out in newtons (N).
这个著名公式表明：合力 (F) 等于质量 (m) 乘以加速度 (a)。若质量以千克 (kg)、加速度以 m/s² 计，则力单位为牛顿 (N)。
6. Weight and Gravitational Field Strength | 重量与重力场强度
Weight is the force of gravity acting on an object. It is not the same as mass; mass is the amount of matter and stays the same everywhere, while weight depends on the gravitational field strength of the planet.
重量是作用在物体上的重力，与质量不同：质量是物质的多少，处处相同；而重量取决于所在星球的重力场强度。
W = m × g
On Earth, the gravitational field strength g is approximately 9.8 N/kg, but in Year 8 we often use 10 N/kg to simplify calculations. Weight is measured in newtons (N).
在地球表面，重力场强度 g 约为 9.8 N/kg，Year 8 常取 10 N/kg 简化计算。重量单位是牛顿 (N)。
7. Density, Mass and Volume | 密度、质量和体积
Density describes how tightly packed the particles in a material are. It is a property that helps identify substances and predict whether objects float or sink.
密度描述材料中粒子排列的紧密程度。这一属性有助于鉴别物质并预测物体漂浮或下沉。
density = mass ÷ volume
ρ = m / V
centimetres (cm³). Density units include kg/m³ and g/cm³. Remember: 1 g/cm³ = 1000 kg/m³.
质量单位为千克 (kg) 或克 (g)，体积单位为立方米 (m³) 或立方厘米 (cm³)。密度单位包括 kg/m³ 和 g/cm³，注意换算 1 g/cm³ = 1000 kg/m³。
8. Pressure in Solids and Liquids | 固体与液体中的压强
Pressure tells us how concentrated a force is over a given area. A sharp knife cuts better because the same force is spread over a smaller area, giving higher pressure.
压强表示力在给定面积上的集中程度。锋利的刀刃更容易切割，因为相同压力作用在更小的面积上，压强更大。
pressure = force ÷ area
P = F / A
ssure increases with depth and density, but this relationship is often explored practically in Year 8 rather than through a formal equation at this stage.
力 (N) 除以面积 (m²) 得到压强，单位为帕斯卡 (Pa)，1 Pa = 1 N/m²。在液体中，压强随深度和密度增加而增大，这一关系在 Year 8 多通过实验探究，暂不要求公式。
9. Hooke’s Law for Springs | 弹簧的胡克定律
When you stretch a spring without overloading it, the extension is directly proportional to the applied force. This is known as Hooke’s Law, and it holds up to the elastic limit of the material.
当你在不超载的情况下拉伸弹簧时，其伸长量与所施加的力成正比。这就是胡克定律，适用于材料弹性极限以内。
F = k × e
Here, F is the force applied (N), e is the extension (m), and k is the spring constant (N/m). A stiffer spring has a larger k value. Plotting force against extension gives a straight line whose gradient equals k.
式中 F 为施加的力 (N)，e 为伸长量 (m)，k 为劲度系数 (N/m)。弹簧越硬，k 值越大。以力–伸长量作图可得一条直线，其斜率即为 k。
10. Moments and the Principle of Moments | 力矩与力矩原理
A moment is the turning effect of a force. It depends on both the size of the force and the perpendicular distance from the pivot to the line of action of the force.
力矩是力的转动效应，它取决于力的大小以及支点到力作用线的垂直距离。
moment = force × perpendicular distance from pivot
M = F × d
Unit: newton-metre (Nm). The Principle of Moments states that for a lever or any object in balance, the total clockwise moments equal the total anticlockwise moments.
单位：牛·米 (Nm)。力矩原理指出，对于杠杆或任何平衡的物体，顺时针力矩总和等于逆时针力矩总和。
11. Work Done, Energy and Power | 功、能与功率
Work is done whenever a force moves an object in the direction of the force. Energy is transferred in the process, and both work and energy are measured in joules (J).
当力使物体沿力的方向移动时，就做了功。此过程中能量发生转移，功和能量的单位都是焦耳 (J)。
work done = force × distance moved in the direction of the force
W = F × d
ich work is done or energy is transferred. It is measured in watts (W), where 1 W = 1 J/s.
功率是做功或能量转移的快慢，单位是瓦特 (W)，1 W = 1 J/s。
power = work done ÷ time taken
P = W / t
In Year 8, energy types include kinetic, gravitational potential, thermal, sound, light and electrical energy. The law of conservation of energy tells us that energy can be changed from one form to another but cannot be created or destroyed.
Year 8 涉及的能类型包括动能、重力势能、热能、声能、光能和电能。能量守恒定律指出，能量可以从一种形式转化为另一种，但不会凭空产生或消失。
12. Electrical Circuits: Current, Voltage and Resistance | 电路：电流、电压与电阻
Electric current is the flow of electric charge around a circuit. It is measured in amperes (A) using an ammeter connected in series. Voltage (potential difference) is the push that drives the current, measured in volts (V) with a voltmeter connected in parallel.
电流是电荷在电路中的定向流动，单位为安培 (A)，用串联的电流表测量。电压（电势差）是驱动电流的“推力”，单位为伏特 (V)，用并联的电压表测量。
resistance (Ω) = voltage (V) ÷ current (A)
R = V / I
Resistance opposes the flow of current and is measured in ohms (Ω). Components like lamps and resistors have resistance. In a series circuit, current is the same everywhere, but the supply voltage is shared across components. In a parallel circuit, the voltage across each branch is the same as the supply, while total current splits among the branches.
电阻阻碍电流流动，单位是欧姆 (Ω)。灯泡和电阻器等元件都具有电阻。串联电路中电流处处相同，但电源电压由各元件分担；并联电路中各支路两端电压与电源电压相等，总电流在支路中分流。
ensive circuit calculations, being able to recall and rearrange R = V / I is a core skill.
虽然 Year 8 对电路计算要求不高，但能够记住并变换 R = V / I 是一项核心技能。
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