📚 Year 7 CAIE Physics: Formula and Theorem Quick Reference Handbook | 7年级CAIE物理：公式定理速查手册
Welcome to your Year 7 CAIE Physics formula and theorem quick reference handbook. This guide compiles the essential equations, laws and definitions you need to master for your Lower Secondary science studies. Use this resource for quick revision before tests and to strengthen your problem-solving skills.
欢迎使用你的7年级CAIE物理公式定理速查手册。本指南汇集了你需要掌握的初中科学物理部分的重要公式、定律和定义。利用这个资源进行考前快速复习，并提升你的解题能力。
1. Physical Quantities and Units | 物理量与单位
re, m), mass (kilogram, kg), time (second, s), temperature (kelvin, K) and many other quantities. Common prefixes help write very large or very small numbers, e.g. kilo- (k, ×10³), centi- (c, ×10⁻²) and milli- (m, ×10⁻³).
在物理中，每个测量值都表示为数字和单位。国际单位制 (SI) 为长度（米，m）、质量（千克，kg）、时间（秒，s）、温度（开尔文，K）等许多物理量提供了标准单位。常用前缀有助于书写非常大或非常小的数字，例如千（k，×10³）、厘（c，×10⁻²）和毫（m，×10⁻³）。
The table below lists the fundamental physical quantities you will use most often. Always write the correct unit after a numerical value.
下表列出了你最常使用的基本物理量。在数值后面务必写上正确的单位。
| Quantity / 量 | Symbol / 符号 | SI Unit / 国际单位 | Unit Symbol / 单位符号 |
|---|---|---|---|
| Length / 长度 | l, s, d | metre / 米 | m |
| Mass / 质量 | m | kilogram / 千克 | kg |
| Time / 时间 | t | second / 秒 | s |
| Temperature / 温度 | T, θ | kelvin / 开尔文 | K |
| Electric current / 电流 | I | ampere / 安培 | A |
cm = 0.01 m and 1 km = 1000 m. Using prefixes correctly avoids very long decimal numbers.
记住单位之间的换算至关重要。例如 1 cm = 0.01 m，1 km = 1000 m。正确使用前缀可以避免出现过长的小数。
2. Speed, Distance and Time | 速度、距离与时间
Speed is a measure of how fast an object moves. The average speed of an object can be calculated by dividing the total distance travelled by the total time taken. The formula is often written as:
速度是衡量物体运动快慢的物理量。平均速度可以用通过的总距离除以所用的总时间来计算。公式通常写作：
v = s / t
where v is speed, s is distance and t is time. The SI unit of speed is metre per second (m/s), but kilometres per hour (km/h) is also common. To convert m/s to km/h, multiply by 3.6.
其中 v 代表速度，s 代表距离，t 代表时间。速度的国际单位是米每秒 (m/s)，但千米每小时 (km/h) 也很常见。要将 m/s 换算为 km/h，乘以 3.6。
A distance–time graph helps visualise motion. A straight, sloping line indicates constant speed; a horizontal line means the object is stationary. The gradient of the line gives the speed.
距离-时间图像有助于直观显示运动。一条倾斜的直线表示匀速运动；一条水平线表示物体静止。直线的斜率（梯度）给出了速度。
3. Density | 密度
Density describes how much mass is packed into a given volume. It helps to compare different materials: a material with a higher density feels heavier for its size. The formula is:
密度描述了给定体积内包含多少质量。它有助于比较不同物质：密度较大的材料在相同体积下感觉更重。公式为：
ρ = m / V
where ρ is density, m is mass and V is volume. The unit is kilogram per cubic metre (kg/m³) or gram per cubic centimetre (g/cm³). Water has a density of about 1 g/cm³ or 1000 kg/m³. An object floats if its density is less than the density of the fluid it is in.
其中 ρ 为密度，m 为质量，V 为体积。单位是千克每立方米 (kg/m³) 或克每立方厘米 (g/cm³)。水的密度约为 1 g/cm³ 或 1000 kg/m³。如果物体的密度小于其所在液体的密度，物体就会漂浮。
To find the volume of an irregular solid, you can use the displacement method with a measuring cylinder.
要测量不规则固体的体积，你可以使用量筒排水法。
4. Forces and Newton's Laws of Motion | 力与牛顿运动定律
A force is a push or a pull that can change an object's speed, direction or shape. Force is measured in newtons (N). Newton's three laws of motion form the foundation of dynamics.
力是一种推或拉，能改变物体的速度、方向或形状。力以牛顿 (N) 为单位度量。牛顿的三大运动定律构成了动力学的基础。
Newton's first law (the law of inertia) states that an object remains at rest or moves at a constant velocity unless acted upon by a resultant force. Newton's second law gives the relationship between resultant force, mass and acceleration:
牛顿第一定律（惯性定律）指出，除非受到合外力的作用，否则物体将保持静止状态或匀速直线运动状态。牛顿第二定律给出了合外力、质量与加速度之间的关系：
F = m a
where F is resultant force in newtons, m is mass in kilograms and a is acceleration in metres per second squared (m/s²). This law explains why a heavier object needs a greater force to accelerate at the same rate.
其中 F 是合外力（牛顿），m 是质量（千克），a 是加速度（米每二次方秒，m/s²）。这一定律解释了为什么较重的物体需要更大的力才能获得相同的加速度。
Newton's third law says: for every action there is an equal and opposite reaction. This means forces always occur in pairs acting on two different objects.
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。这意味着力总是成对出现，作用在两个不同的物体上。
5. Pressure | 压强
Pressure is a measure of how concentrated a force is over an area. A sharp knife cuts easily because it exerts high pressure due to its small area. The formula is:
压强度量的是力在一个面积上的集中程度。锋利的刀容易切割，因为由于面积小，它产生了很大的压强。公式为：
p = F / A
crease pressure, you can increase the force or decrease the area; to decrease pressure, do the opposite.
其中 p 为压强（帕斯卡，Pa），F 为力（牛顿，N），A 为面积（平方米，m²）。1 Pa = 1 N/m²。要增大压强，可以增大作用力或减小受力面积；要减小压强，则相反。
6. Energy, Work and Power | 能量、功与功率
Energy is the ability to do work and is measured in joules (J). Work is done when a force moves an object in the direction of the force. The work done is given by:
能量是做功的能力，以焦耳 (J) 为单位。当一个力使物体沿着力的方向移动时，力就做了功。所做的功由下式给出：
W = F × d
where W is work done, F is force and d is distance moved in the direction of the force. Lifting an object increases its gravitational potential energy (GPE):
其中 W 为功，F 为力，d 为沿力方向移动的距离。举起一个物体会增加它的重力势能 (GPE)：
Eₚ = m g h
ength (≈ 10 N/kg on Earth) and h is height. A moving object possesses kinetic energy (KE):
其中 Eₚ 是重力势能，m 是质量，g 是引力场强度（地球约 10 N/kg），h 是高度。运动的物体具有动能 (KE)：
Eₖ = ½ m v²
Power is the rate of doing work or transferring energy. It is calculated by dividing work done or energy transferred by time:
功率是做功或能量转移的速率。它等于所做的功或转移的能量除以时间：
P = W / t
The unit of power is the watt (W), where 1 W = 1 J/s.
功率的单位是瓦特 (W)，1 W = 1 J/s。
7. Electric Circuits and Ohm's Law | 电路与欧姆定律
An electric circuit provides a path for current to flow. Current (I) is the rate of flow of charge and is measured in amperes (A). Voltage (V) is the energy transferred per unit charge, measured in volts (V). Resistance (R) measures how difficult it is for current to flow, in ohms (Ω). These three quantities are linked by Ohm's law:
电路为电流提供流动的通路。电流 (I) 是电荷流动的速率，单位为安培 (A)。电压 (V) 是每单位电荷转移的能量，单位为伏特 (V)。电阻 (R) 衡量电流流动的难易程度，单位为欧姆 (Ω)。这三个量由欧姆定律联系起来：
V = I × R
This law holds for many conductors at constant temperature. In series circuits, the current is the same everywhere, the total voltage is the sum of individual voltages and the total resistance is the sum of individual resistances:
这一规律在恒温条件下适用于许多导体。在串联电路中，各处电流相等，总电压等于各用电器电压之和，总电阻等于各电阻之和：
Rₜₒₜₐₗ = R₁ + R₂ + ...
In parallel circuits, the voltage across each branch is the same, the total current is the sum of branch currents and the total resistance is given by:
在并联电路中，各支路两端电压相等，干路电流等于各支路电流之和，总电阻由下式给出：
1/Rₜₒₜₐₗ = 1/R₁ + 1/R₂ + ...
Always use an ammeter in series to measure current and a voltmeter in parallel to measure voltage.
测量电流时安培表应串联，测量电压时伏特表应并联。
8. Wave Properties and Reflection | 波的性质与反射
Waves transfer energy without transferring matter. The wave speed (v), frequency (f) and wavelength (λ) are related by the wave equation:
波传递能量而不传递物质。波速 (v)、频率 (f) 和波长 (λ) 由波动方程联系起来：
v = f λ
where v is in m/s, f is in hertz (Hz) and λ is in metres (m). Frequency is the number of complete waves passing a point per second. Sound waves need a medium to travel, while light waves can travel through a vacuum.
其中 v 以 m/s 为单位，f 以赫兹 (Hz) 为单位，λ 以米 (m) 为单位。频率是每秒钟通过某点的完整波的数目。声波需要介质才能传播，而光波可以在真空中传播。
Both angles are measured from the normal, an imaginary line perpendicular to the surface.
反射定律指出，对于光滑表面，入射角等于反射角：i = r。两个角都是从法线（垂直于表面的假想线）开始测量。
Light travels in straight lines; this explains shadow formation. Sound can reflect to produce echoes.
光沿直线传播；这解释了影子的形成。声波反射可以产生回声。
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