KS3 Cambridge Physics: Formula and Theorem Quick Reference Handbook | KS3 Cambridge 物理：公式定理速查手册

📚 KS3 Cambridge Physics: Formula and Theorem Quick Reference Handbook | KS3 Cambridge 物理：公式定理速查手册

This handbook provides a concise summary of all the essential formulas and principles you need for the KS3 Cambridge Physics course. It is designed for quick revision and easy reference, covering motion, forces, energy, electricity, waves, and more.

本手册为 KS3 Cambridge 物理课程总结所有重要的公式和定理，方便快速复习和查阅。涵盖运动、力、能量、电学、波等内容。

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1. Speed, Distance and Time | 速度、距离与时间

Speed tells us how fast an object is moving. Average speed, distance and time are linked by a simple relationship.

速度表示物体运动的快慢。平均速度、距离和时间之间存在简单的关系。

speed = distance ÷ time

In symbols, we write v = d / t, where v is speed, d is distance travelled and t is the time taken.

用符号表示为 v = d / t，其中 v 是速度，d 是移动距离，t 是所用时间。

Speed is measured in metres per second (m/s), distance in metres (m) and time in seconds (s). For example, if a runner covers 400 m in 50 s, her average speed is 400 ÷ 50 = 8 m/s.

速度的单位是米每秒（m/s），距离的单位是米（m），时间的单位是秒（s）。例如，一名跑步者 50 秒内跑完 400 米，她的平均速度为 400 ÷ 50 = 8 m/s。

Other common units include kilometres per hour (km/h). To convert m/s to km/h, multiply by 3.6.

其他常用单位包括千米每小时（km/h）。将 m/s 转换为 km/h 时，乘以 3.6。

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2. Density | 密度

Density measures how much mass is packed into a given volume. It is a property of a material and helps identify substances.

密度衡量单位体积所含的质量，是物质的一种特性，可用于鉴别物质。

density = mass ÷ volume

Using symbols: ρ = m / V (the Greek letter rho, ρ, represents density).

用符号表示：ρ = m / V（希腊字母 ρ 表示密度）。

The SI unit is kilograms per cubic metre (kg/m³), but for solids and liquids we often use grams per cubic centimetre (g/cm³). For instance, a block of mass 200 g and volume 50 cm³ has a density of 200 ÷ 50 = 4 g/cm³.

国际单位是千克每立方米（kg/m³），但对于固体和液体常用克每立方厘米（g/cm³）。例如，一块质量为 200 g、体积为 50 cm³ 的物体，密度为 200 ÷ 50 = 4 g/cm³。

1 g/cm³ is equivalent to 1000 kg/m³. Water has a density of 1 g/cm³.

1 g/cm³ 相当于 1000 kg/m³。水的密度是 1 g/cm³。

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3. Forces and Motion (Newton’s Second Law) | 力与运动（牛顿第二定律）

A resultant force causes an object to accelerate. The acceleration depends on the mass of the object and the size of the force.

合力使物体产生加速度。加速度取决于物体的质量和力的大小。

force = mass × acceleration

In symbol form: F = m a. Force is measured in newtons (N), mass in kilograms (kg) and acceleration in metres per second squared (m/s²).

符号形式：F = m a。力的单位是牛顿（N），质量的单位是千克（kg），加速度的单位是米每二次方秒（m/s²）。

This is Newton’s Second Law of Motion. If a force of 10 N acts on a 2 kg trolley, the acceleration a = F / m = 10 / 2 = 5 m/s².

这是牛顿第二运动定律。如果 10 N 的力作用于 2 kg 的小车上，加速度 a = F / m = 10 / 2 = 5 m/s²。

The greater the mass, the smaller the acceleration for the same force. This explains why heavier objects are harder to speed up or slow down.

同等力下质量越大，加速度越小。这解释了为什么较重的物体更难加速或减速。

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4. Pressure | 压强

Pressure is the force exerted per unit area. It tells us how concentrated a force is.

压强是单位面积上所受的力，表示力的集中程度。

pressure = force ÷ area

In symbols: P = F / A, where P is pressure in pascals (Pa) or N/m², F is force in newtons (N), and A is area in square metres (m²).

符号：P = F / A，其中 P 是压强，单位帕斯卡（Pa）或 N/m²，F 是力（N），A 是面积（m²）。

For example, a force of 500 N acting on an area of 0.1 m² produces a pressure of 500 ÷ 0.1 = 5000 Pa.

例如，500 N 的力作用在 0.1 m² 的面积上，产生的压强为 500 ÷ 0.1 = 5000 Pa。

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