📚 Year 8 CAIE Physics: Formula & Theorem Quick Reference Handbook | Year 8 CAIE 物理：公式定理速查手册
This quick reference handbook provides all the essential formulas and theorems for Year 8 CAIE Physics. Mastering these equations will help you solve problems in motion, forces, energy, waves, and electricity.
本速查手册包含 Year 8 CAIE 物理所有重要公式和定理。掌握这些方程将帮助你解决运动、力、能量、波和电学中的问题。
1. Speed, Distance and Time | 速度、距离和时间
Average speed is calculated by dividing the total distance travelled by the total time taken. The formula is v = d / t, where v is speed (m/s), d is distance (m), and t is time (s).
平均速度等于总路程除以总时间。公式为 v = d / t，其中 v 为速度（米/秒），d 为距离（米），t 为时间（秒）。
You can rearrange the equation to find distance: d = v × t, or to find time: t = d / v.
你可以将公式变形求距离：d = v × t，或求时间：t = d / v。
2. Acceleration | 加速度
Acceleration is the rate of change of velocity. It is given by a = (v - u) / t, where a is acceleration (m/s²), v is final velocity (m/s), u is initial velocity (m/s), and t is time (s).
加速度是速度变化的快慢。由 a = (v - u) / t 计算，其中 a 为加速度（米/秒²），v 为末速度（米/秒），u 为初速度（米/秒），t 为时间（秒）。
A positive acceleration means speeding up; a negative acceleration means slowing down (deceleration).
正加速度表示加速；负加速度表示减速。
3. Mass, Weight and Gravity | 质量、重量与重力
Weight is the force of gravity acting on an object. It is calculated by W = m × g eight (N), m is mass (kg), and g is gravitational field strength (on Earth, g ≈ 9.8 N/kg).
重量是作用在物体上的重力。由 W = m × g 计算，W 为重量（牛顿），m 为质量（千克），g 为重力场强度（地球上的 g ≈ 9.8 牛/千克）。
Note: Mass is constant everywhere, but weight changes with gravity.
注意：质量处处相同，但重量随重力变化。
4. Density | 密度
Density measures how much mass is packed into a given volume. The formula is ρ = m / V, where ρ (rho) is density (kg/m³), m is mass (kg), and V is volume (m³).
密度衡量单位体积内所含的质量。公式为 ρ = m / V，ρ (rho) 为密度（千克/立方米），m 为质量（千克），V 为体积（立方米）。
To find mass or volume, rearrangements are m = ρ × V and V = m / ρ.
求质量或体积可变形得 m = ρ × V 和 V = m / ρ。
5. Newton's Second Law of Motion | 牛顿第二运动定律
Newton's Second Law states that the resultant force on an object equals its mass times its acceleration: F = m × a, where F is force (N), m is mass (kg), and a is acceleration (m/s²).
牛顿第二定律指出，物体所受的合力等于其质量乘以加速度：F = m × a，其中 F 为力（牛），m 为质量（千克），a 为加速度（米/秒²）。
This law explains why a larger force is needed to accelerate a more massive object.
该定律解释了为什么加速质量更大的物体需要更大的力。
6. Pressure | 压强
Pressure is the force acting per unit area. For solids, P = F / A, where P is pressure (Pa or N/m²), F is force (N), and A is area (m²).
压强是单位面积上所受的压力。对于固体，P = F / A，其中 P 为压强（帕斯卡或牛/平方米），F 为力（牛），A 为面积（平方米）。
In liquids, pressure increases with depth according to P = ρ × g × h, where ρ is the liquid density (kg/m³), g is gravity (N/kg), and h is depth (m).
在液体中，压强随深度增加，公式为 P = ρ × g × h，其中 ρ 为液体密度（千克/立方米），g 为重力（牛/千克），h 为深度（米）。
7. Work and Mechanical Energy | 功与机械能
Work is done when a force moves an object. W = F × d, with work W in joules (J), force F in newtons (N), and distance d in metres (m) moved in the direction of the force.
当力使物体移动时做功。W = F × d，功 W 单位为焦耳 (J)，力 F 单位为牛顿 (N)，距离 d 为沿力的方向移动的米数 (m)。
Gravitational potential energy (GPE) is the energy stored due to height: GPE = m × g × h, where h is height (m).
重力势能 (GPE) 是因高度而储存的能量：GPE = m × g × h，其中 h 为高度 (m)。
Kinetic energy (KE) is the energy of motion: KE = ½ × m × v², where v is speed (m/s).
动能 (KE) 是运动的能量：KE = ½ × m × v²，其中 v 为速度 (m/s)。
8. Power and Efficiency | 功率与效率
Power is the rate of doing work or transferring energy. P = W / t, where P is power in watts (W), W is work done or energy transferred (J), and t is time (s).
功率是做功或能量转移的速率。P = W / t，其中 P 为功率（瓦特），W 为做功或转移的能量（焦耳），t 为时间（秒）。
Efficiency measures how well energy is converted into useful output. It is usually given as a percentage: Efficiency = (useful energy output / total energy input) × 100%. No machine is 100% efficient.
效率衡量能量转化为有用输出的比例。通常表示为百分比：效率 = (有用能量输出 / 总能量输入) × 100%。没有机器能达到 100% 的效率。
9. Moments and Levers | 力矩与杠杆
The moment of a force (torque) is the turning effect about a pivot. Moment = F × d, where F is the force (N) and d is the perpendicular distance from the pivot to the line of action of the force (m). Units are newton-metres (Nm).
力矩是力绕支点的转动效应。力矩 = F × d，其中 F 为力 (N)，d 为从支点到力作用线的垂直距离 (m)。单位是牛·米 (Nm)。
The Principle of Moments states that for a system in equilibrium, the sum of clockwise moments equals the sum of anticlock
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