📚 Year 7 CIE Physics Quick-Reference Formula & Theorem Handbook | 剑桥 CIE 7 年级物理公式定理速查手册
Welcome to your go-to revision guide for Year 7 CIE Physics. This handbook brings together all the essential formulas, laws, and key definitions you need for the Checkpoint curriculum, presented in a clear, bilingual format to support both English and Chinese learners. Use it to reinforce your understanding, check tricky points, and build confidence for tests and final assessments.
欢迎使用这份为 CIE 7 年级物理量身打造的速查手册。本手册汇集了所有 Checkpoint 课程必备的公式、定律和关键定义，采用清晰的双语呈现，帮助中英文学习者巩固理解、查漏补缺，并在测验和期末考试中建立信心。
1. Speed, Distance and Time | 速度、距离与时间
Speed tells us how fast an object is moving. The relationship between speed, distance and time is one of the most important formulas in Year 7 physics.
速度表示物体运动的快慢。速度、距离和时间之间的关系是 7 年级物理中最重要的公式之一。
speed = distance ÷ time
速度 = 距离 ÷ 时间
You can rearrange this into a triangle to help remember: distance on top, speed and time on the bottom. Always check that units match – for example, metres per second (m/s) when distance is in metres and time in seconds.
你可以用公式三角形来帮助记忆：距离在上方，速度和并排在下方。务必检查单位是否一致——例如，当距离用米、时间用秒时，速度的单位就是米每秒 (m/s)。
Common units: metre per second (m/s), kilometre per hour (km/h). To convert m/s to km/h, multiply by 3.6. Average speed is used when speed changes during a journey.
常用单位：米每秒 (m/s)、千米每小时 (km/h)。从 m/s 换算到 km/h 乘以 3.6。当运动过程中速度变化时，我们使用平均速度。
2. Acceleration | 加速度
Acceleration measures how quickly velocity changes. In Year 7, we focus on uniform acceleration in a straight line.
加速度衡量速度变化的快慢。在 7 年级，我们主要学习直线上的匀加速度运动。
acceleration = change in velocity ÷ time taken
加速度 = 速度变化量 ÷ 所用时间
The unit is metre per second squared (m/s²). If an object slows down, the acceleration is negative – sometimes called deceleration or retardation.
单位是米每平方秒 (m/s²)。如果物体减速，加速度为负值，有时也称为减速度或负加速度。
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.
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大小。
weight = mass × gravitational field strength
重量 = 质量 × 引力场强度
On Earth, gravitational field strength g is about 10 N/kg (more precisely 9.8 N/kg). Weight is a force, so it is measured in newtons (N). Your mass stays the same on the Moon, but your weight is smaller because the Moon's gravity is weaker.
地球表面的引力场强度 g 约为 10 N/kg（精确值 9.8 N/kg）。重量是一种力，因此单位是牛顿 (N)。在月球上，你的质量不变，但重量会变小，因为月球的引力较弱。
4. Density | 密度
Density tells us how tightly packed the particles are in a material. It links mass and volume.
密度表示材料中粒子的密集程度，将质量与体积联系起来。
density = mass ÷ volume
密度 = 质量 ÷ 体积
Common units are kilograms per metre cubed (kg/m³) or grams per centimetre cubed (g/cm³). Solids are usually denser than liquids, and liquids denser than gases, but there are exceptions like wood floating on water.
常用单位是千克每立方米 (kg/m³) 或克每立方厘米 (g/cm³)。固体通常比液体密度大，液体比气体密度大，但也有例外，比如木头能浮在水面上。
5. Pressure | 压强
Pressure measures how concentrated a force is over an area. This is why sharp knives cut better – they apply force over a very small area.
压强衡量力在面积上的集中程度。这就是为什么锋利的刀具切起来更轻松——它们在很小的面积上施加力。
pressure = force ÷ area
压强 = 力 ÷ 面积
. Pressure in liquids increases with depth and density; pressure in gases can be explained by particle collisions.
单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。液体中的压强随深度和密度增加而增大；气体压强可用粒子碰撞来解释。
6. Energy, Work and Power | 能量、功与功率
Energy is the ability to do work. Work is done when a force moves an object in the direction of the force.
能量是做功的本领。当力使物体沿力的方向移动时，我们就说力做了功。
work done = force × distance moved in direction of force
功 = 力 × 沿力方向移动的距离
Power is the rate at which work is done or energy is transferred.
功率是做功或能量传递的速率。
power = work done ÷ time taken
功率 = 功 ÷ 时间
f energy: kinetic, gravitational potential, thermal, chemical, electrical, light, sound, nuclear.
能量的单位是焦耳 (J)，功率的单位是瓦特 (W)，1 W = 1 J/s。能量的形式有：动能、重力势能、热能、化学能、电能、光能、声能、核能等。
7. Kinetic and Potential Energy | 动能与势能
Kinetic energy is the energy of motion. Gravitational potential energy is stored energy due to height.
动能是物体因运动而具有的能量。重力势能是因高度而储存的能量。
kinetic energy = ½ × mass × speed²
动能 = ½ × 质量 × 速度²
GPE = mass × g × height
重力势能 = 质量 × g × 高度
In many systems, energy transfers between kinetic and potential forms, such as in a pendulum or roller coaster. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed.
在许多系统中，能量在动能和势能之间相互转化，例如钟摆或过山车。能量守恒定律指出，能量既不会凭空产生，也不会凭空消失，它只能从一种形式转化为另一种形式，或者从一个物体转移到另一个物体。
8. Efficiency | 效率
No energy transfer is perfect; some energy is always dissipated as thermal energy. Efficiency tells us how much of the input energy is usefully transferred.
任何能量传递都不是完美的，总有一部分能量以热能形式耗散。效率告诉我们输入能量中有多少被有效利用。
efficiency = (useful output energy ÷ total input energy) × 100%
效率 = (有用的输出能量 ÷ 总输入能量) × 100%
so be calculated using power: efficiency = (useful power output ÷ total power input) × 100%. It is always less than 100% in real systems due to friction and air resistance.
也可以用功率计算效率：效率 = (有用的输出功率 ÷ 总输入功率) × 100%。由于摩擦和空气阻力，实际系统的效率总是小于 100%。
9. Electric Current, Voltage and Resistance | 电流、电压与电阻
Current is the flow of electric charge. Voltage (potential difference) is the push that drives the current. Resistance opposes the flow.
电流是电荷的定向移动。电压（电势差）是推动电荷流动的驱动力。电阻则阻碍电荷流动。
V = I × R
电压 = 电流 × 电阻
Units: voltage in volts (V), current in amperes (A), resistance in ohms (Ω). In a series circuit, current is the same everywhere; in parallel circuits, current splits and voltage is the same across branches.
单位：电压为伏特 (V)，电流为安培 (A)，电阻为欧姆 (Ω)。串联电路中各处电流相等；并联电路中电流分流，各支路两端电压相等。
10. Series and Parallel Circuit Rules | 串并联电路规则
Understanding circuit rules helps predict what meters will read. Here are the key rules for current and voltage in circuits.
理解电路规则有助于预测电表读数。以下是电路中电流和电压的关键规则。
| Series | Parallel | |
|---|---|---|
| Current | Same at all points (I₁ = I₂ = I₃) | Splits across branches (Itotal = I₁ + I₂) |
| Voltage | Shared across components (Vtotal = V₁ + V₂) | Same across each branch (V₁ = V₂ = Vtotal) |
| Resistance | Total R = R₁ + R₂ + ... | 1/Rtotal = 1/R₁ + 1/R₂ + ... |
中文对应下表：
| 串联 | 并联 | |
|---|---|---|
| 电流 | 各处相等 (I₁ = I₂ = I₃) | 干路电流等于各支路电流之和 (Itotal = I₁ + I₂) |
| 电压 | 总电压等于各部分电压之和 (Vtotal = V₁ + V₂) | 各支路电压相等，等于总电压 (V₁ = V₂ = Vtotal) |
| 电阻 | 总电阻等于各电阻之和 Rtotal = R₁ + R₂ + ... | 总电阻的倒数等于各支路电阻倒数之和 1/Rtotal = 1/R₁ + 1/R₂ + ... |
These rules are essential for analysing simple circuits and for practical investigations.
这些规则对于分析简单电路和进行实验探究至关重要。
11. Wave Properties | 波的特性
Waves transfer energy without transferring matter. Key wave quantities are frequency, wavelength, amplitude and wave speed.
波传递能量而不传递物质。波的基本物理量包括频率、波长、振幅和波速。
wave speed = frequency × wavelength
波速 = 频率 × 波长
Frequency is measured in hertz (Hz), wavelength in metres (m). Transverse waves (e.g., light, water ripples) have oscillations perpendicular to wave direction. Longitudinal waves (e.g., sound) have oscillations parallel.
频率的单位是赫兹 (Hz)，波长的单位是米 (m)。横波（如光波、水波）的振动方向与传播方向垂直。纵波（如声波）的振动方向与传播方向平行。
lates to loudness (sound) or brightness (light). The period T = 1/f, where f is frequency.
振幅与声音的响度或光的亮度有关。周期 T = 1/f，其中 f 是频率。
12. Reflection and Refraction Laws | 反射定律与折射
The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal.
反射定律指出，入射角等于反射角，这两个角都从法线量起。
angle of incidence = angle of reflection
入射角 = 反射角
When light passes from one medium to another (e.g., air to glass), it bends. This bending is called refraction. Refraction happens because the speed of light changes in different media.
当光从一种介质进入另一种介质（如空气到玻璃）时，会发生弯折，这一现象称为折射。折射是由于光在不同介质中的传播速度不同而引起的。
For light entering a denser medium, the ray bends towards the normal; leaving a denser medium, it bends away from the normal.
光进入光密介质时，光线向法线偏折；离开光密介质时，光线偏离法线。
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