📚 Year 8 AQA Physics Formula & Theorem Quick-Reference Handbook | 物理公式定理速查手册
This handbook is your one‑stop revision guide to the most important formulas, laws and principles covered in Year 8 AQA Physics. Each topic is presented with a straightforward equation, clear notation and practical tips for using it in calculations and experiments.
本手册是Year 8 AQA物理课程中最重要的公式、定律和原理一站式复习指南。每个主题都配有简洁的公式、清晰的符号以及在计算和实验中应用公式的实用提示。
1. Speed, Distance and Time | 速度、距离与时间
Speed tells us how fast an object is moving. It is defined as the distance travelled in a certain amount of time. When motion is steady, the average speed can be found using a simple equation.
速度告诉我们物体运动的快慢，它定义为单位时间内通过的距离。当运动匀速时，平均速度可用一个简单的公式计算。
average speed = distance ÷ time
平均速度 = 距离 ÷ 时间
The standard unit of speed is metres per second (m/s). Distances are often measured in metres (m) and time in seconds (s). In everyday contexts you may also see kilometres per hour (km/h).
速度的标准单位是米每秒（m/s）。距离通常以米（m）为单位，时间以秒（s）为单位。在日常生活中你也会见到千米每小时（km/h）。
A distance‑time graph shows how far an object has moved over a period. A steeper slope means a higher speed, and a horizontal line means the object is stationary.
距离-时间图显示物体在一段时间内移动了多远。斜率越陡表示速度越快，水平线则表示物体静止。
2. Weight and Mass | 重量与质量
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. The two are related but not the same thing – mass does not change with location, whereas weight can.
质量是物体所含物质的多少，以千克（kg）为单位。重量是作用在物体上的重力。两者相关但并非同一概念——质量不随位置改变，而重量则会变化。
weight = mass × gravitational field strength
重量 = 质量 × 重力场强度
On Earth the gravitational field strength (g) is about 9.8 N/kg, but for Year 8 calculations we often use 10 N/kg. Weight is a force, so it is measured in newtons (N).
地球表面的重力场强度（g）约为 9.8 牛/千克，但在Year 8的计算中我们通常使用 10 牛/千克。重量是一种力，因此以牛顿（N）为单位。
Always check whether a question asks for mass or weight before you apply the formula.
在应用公式前，务必先确认题目问的是质量还是重量。
3. Density | 密度
Density describes how tightly packed the particles in a substance are. It links mass and volume, and can help you predict whether an object will float or sink.
密度描述物质中粒子排列的紧密程度。它把质量和体积联系起来，能帮助你预测一个物体是浮还是沉。
density = mass ÷ volume
密度 = 质量 ÷ 体积
Common units for density are kilograms per metre cubed (kg/m³) and grams per centimetre cubed (g/cm³). For solids and liquids, mass is usually in grams or kilograms and volume in cm³ or m³.
密度的常用单位是千克每立方米（kg/m³）和克每立方厘米（g/cm³）。对固体和液体来说，质量常用克或千克，体积常用立方厘米或立方米。
Objects with a density lower than that of water (1 g/cm³) tend to float, while denser objects sink.
密度小于水（1 g/cm³）的物体往往会漂浮，密度更大的物体则会下沉。
4. Pressure | 压强
Pressure measures how concentrated a force is over a certain area. A sharp knife cuts easily because it applies a large force over a tiny area, producing high pressure.
压强衡量力在一定面积上的集中程度。锋利的刀容易切割，因为它在很小的面积上施加了很大的力，产生很高的压强。
pressure = force ÷ area
压强 = 力 ÷ 面积
The unit of pressure is the pascal (Pa), where 1 Pa equals 1 newton per square metre (N/m²). Large pressures are often given in kilopascals (kPa).
压强的单位是帕斯卡（Pa），1 Pa 等于 1 牛/平方米（N/m²）。较大的压强常用千帕（kPa）表示。
Increasing the area over which a force acts reduces the pressure – that is why snowshoes stop you from sinking into soft snow.
增大力的作用面积可减小压强——这就是雪鞋能防止你陷入松软的雪里的原因。
5. Hooke’s Law | 胡克定律
Hooke’s Law describes the behaviour of springs and elastic materials when they are stretched or compressed. The extension of a spring is directly proportional to the force applied, provided the elastic limit is not exceeded.
胡克定律描述了弹簧及弹性材料在被拉伸或压缩时的行为。只要不超过弹性限度，弹簧的伸长量与施加的力成正比。
force = spring constant × extension
力 = 劲度系数 × 伸长量
The spring constant (k) is measured in newtons per metre (N/m) and tells you how stiff a spring is. A high spring constant means a stiffer spring that is harder to stretch.
劲度系数（k）的单位是牛/米（N/m），它表示弹簧的软硬程度。劲度系数越大，弹簧越硬，越难拉伸。
On a force‑extension graph, Hooke’s Law appears as a straight line through the origin. As soon as the line begins to curve, the elastic limit has been passed and the material will no longer return to its original shape.
在力-伸长量图中，胡克定律表现为一条过原点的直线。一旦线条开始弯曲，就说明超过了弹性限度，材料不再能恢复原状。
6. Moments (Turning Forces) | 力矩（转动效应）
A moment is the turning effect of a force around a pivot. It depends on both the size of the force and how far it is applied from the pivot.
力矩是力绕支点产生的转动效应，它取决于力的大小以及力作用点与支点的距离。
moment = force × perpendicular distance from pivot
力矩 = 力 × 力臂（支点到力作用线的垂直距离）
Moments are measured in newton metres (Nm). To increase the turning effect, you can either apply a larger force or increase the distance from the pivot – exactly the principle behind a long spanner making it easier to undo a tight nut.
力矩的单位是牛·米（Nm）。要增大转动效应，可以施加更大的力，也可以增大与支点的距离——长扳手之所以更容易拧松紧锁的螺母，正是运用了这个原理。
When an object is balanced, the total clockwise moment equals the total anticlockwise moment. This is the principle of moments and is used to solve many equilibrium problems.
当物体平衡时，顺时针力矩之和等于逆时针力矩之和。这就是力矩原理，常用于解决许多平衡问题。
7. Work and Energy Transfer | 功与能量转移
Work is done whenever a force moves an object in the direction of the force. Energy is transferred mechanically from one store to another. The amount of work done tells you how much energy has been shifted.
只要力使物体沿力的方向移动，就做了功。能量通过机械方式从一个储存库转移到另一个储存库。做功的多少表示转移了多少能量。
work done = force × distance
做功 = 力 × 距离
Both work and energy are measured in joules (J). One joule is the work done when a force of 1 newton moves an object 1 metre in the direction of the force.
功和能量的单位都是焦耳（J）。1 焦耳相当于 1 牛·米的力使物体沿力的方向移动 1 米所做的功。
When an object is lifted against gravity, the work done is equal to the weight multiplied by the height gained. Efficiency can be calculated as the useful output energy divided by the total input energy, often expressed as a percentage.
当物体被克服重力提升时，所做的功等于重量乘以升高的高度。效率可通过有用的输出能量除以总输入能量来计算，通常以百分比表示。
8. Power | 功率
Power tells you how quickly energy is transferred or how quickly work is done. A powerful machine does the same work in less time.
功率表示能量转移的快慢或做功的快慢。功率大的机器能在更短的时间内完成同样的功。
power = work done ÷ time
功率 = 做功 ÷ 时间
Alternatively, power can be expressed as energy transferred divided by time. Power is measured in watts (W): 1 watt equals 1 joule per second (J/s). Larger powers are given in kilowatts (kW).
功率也可表示为单位时间内转移的能量。功率的单位是瓦特（W）：1 瓦特等于 1 焦耳/秒（J/s）。较大的功率用于千瓦（kW）表示。
Comparing the power ratings of different appliances helps you understand which one uses energy faster.
比较不同电器的额定功率有助于你理解哪一个消耗能量更快。
9. Ohm’s Law and Electric Current | 欧姆定律与电流
Current is the flow of electric charge around a circuit. Ohm’s Law links the potential difference (voltage) across a component, the current through it and its resistance.
电流是电荷在电路中的流动。欧姆定律将元件两端的电势差（电压）、通过它的电流以及它的电阻联系起来。
current = charge ÷ time
电流 = 电荷量 ÷ 时间
potential difference = current × resistance
电压 = 电流 × 电阻
Current is measured in amperes or amps (A), charge in coulombs (C), potential difference in volts (V) and resistance in ohms (Ω). For a fixed resistor at constant temperature, the voltage‑current graph is a straight line.
电流的单位是安培（A），电荷的单位是库仑（C），电压的单位是伏特（V），电阻的单位是欧姆（Ω）。对于恒温下的定值电阻，电压-电流图是一条直线。
Always connect voltmeters in parallel and ammeters in series when taking measurements.
测量时，电压表应并联接入电路，电流表应串联接入电路。
10. Wave Speed | 波速
Waves transfer energy without transferring matter. The speed of a wave depends on its frequency and wavelength. This relationship holds for all kinds of waves, including sound, water and light.
波传递能量而不传递物质。波速取决于波的频率和波长。这个关系适用于所有类型的波，包括声波、水波和光波。
wave speed = frequency × wavelength
波速 = 频率 × 波长
Wave speed is measured in metres per second (m/s), frequency in hertz (Hz) and wavelength in metres (m). In transverse waves the oscillations are perpendicular to the direction of energy transfer; in longitudinal waves the oscillations are parallel.
波速的单位是米每秒（m/s），频率的单位是赫兹（Hz），波长的单位是米（m）。横波
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