📚 Year 8 CCEA Physics Formula & Theorem Quick Reference | Year 8 CCEA 物理：公式定理速查手册
This quick reference guide compiles all the essential formulas and theorems needed for Year 8 CCEA Physics. Mastering these equations will help you solve problems on motion, forces, energy and electricity with confidence. Each section presents the formula, explains the symbols and states the standard units.
本速查手册汇集了 Year 8 CCEA 物理所需的所有关键公式与定理。掌握这些方程能帮助你自信地解决运动、力、能量与电学问题。每一部分给出公式、解释符号并注明标准单位。
1. Speed, Distance and Time | 速度、距离与时间
ind distance s = v × t, or time t = s ÷ v. Speed is measured in metres per second (m/s), distance in metres (m) and time in seconds (s).
速度是距离对时间的变化率。速度(v)、距离(s)和时间(t)之间的关系式为：v = s ÷ t。该公式可变形为求距离 s = v × t，或求时间 t = s ÷ v。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)。
2. Density | 密度
e ρ is density, m is mass and V is volume. Density is expressed in kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). Mass is in kg or g, volume in m³ or cm³.
密度是物质单位体积的质量，计算公式为：ρ = m ÷ V，其中 ρ 为密度，m 为质量，V 为体积。密度的单位是千克每立方米(kg/m³)或克每立方厘米(g/cm³)。质量单位为 kg 或 g，体积单位为 m³ 或 cm³。
3. Pressure | 压强
pascals (Pa), where 1 Pa = 1 N/m². A larger area reduces pressure for the same force.
压强是作用在单位面积上的力。力 F 作用在面积 A 上产生的压强 P 为：P = F ÷ A。压强的单位是帕斯卡(Pa)，1 Pa = 1 N/m²;。在力不变的情况下，面积越大压强越小。
4. Moments and Levers | 力矩与杠杆
ce in newtons (N) and d is the perpendicular distance from the pivot to the line of action of the force, in metres (m). Moment is measured in newton-metres (Nm). For an object to be in rotational equilibrium, the sum of clockwise moments must equal the sum of anticlockwise moments.
力的转动效应称为力矩。力矩计算公式为：M = F × d，其中 F 为力（牛顿,N），d 为支点到力作用线的垂直距离（米,m）。力矩的单位是牛顿·米(Nm)。物体处于转动平衡时，顺时针力矩之和必须等于逆时针力矩之和。
For a lever at equilibrium: effort × effort distance = load × load distance (F1 × d1 = F2 × d2). This means a small effort can lift a heavy load when applied at a greater distance from the pivot.
杠杆是利用力矩原理的简单机械。杠杆平衡时：动力 × 动力臂 = 阻力 × 阻力臂 (F1 × d1 = F2 × d2)。这意味着在远离支点处施加较小的动力就可以举起较重的负载。
5. Work Done | 做功
× d. Work is measured in joules (J). 1 J = 1 N m. If there is no movement, no work is done.
力作用于物体并使其在力的方向上移动时，力就做了功。做功 W 等于力 F 与沿力方向移动的距离 d 的乘积：W = F × d。功的单位是焦耳(J)，1 J = 1 N m。如果没有移动，就没有做功。
6. Power | 功率
oules (J), E is energy transferred in joules (J) and t is time in seconds (s). Power is measured in watts (W). 1 W = 1 J/s.
功率是做功或能量转化的快慢。功率 P 的计算公式为：P = W ÷ t，或等价于 P = E ÷ t，其中 W 为做功（J），E 为转移的能量（J），t 为时间（s）。功率的单位是瓦特(W)，1 W = 1 J/s。
7. Kinetic Energy | 动能
Kinetic energy is the energy an object has due to its motion. It is calculated with: Ek mass in kilograms (kg) and v is the speed in metres per second (m/s). The kinetic energy Ek is measured in joules (J). Doubling the speed quadruples the kinetic energy.
动能是物体由于运动而具有的能量，计算公式为：Ek = ½ m v²;，其中 m 为质量（kg），v 为速度（m/s）。动能 Ek 的单位是焦耳(J)。速度增加为原来的两倍，动能将变为原来的四倍。
8. Gravitational Potential Energy | 重力势能
Gravitational potential energy (GPE) is the energy stored in an object lifted against gravity. The GPE is given by: Ep vitational field strength (on Earth g ≈ 10 N/kg) and h is the height above the reference level in metres (m). GPE is measured in joules (J).
重力势能是物体在重力作用下被举高而储存的能量。重力势能公式为：Ep = m g h，其中 m 为质量（kg），g 为重力场强度（地球上 g ≈ 10 N/kg），h 为相对于参考面的高度（m）。重力势能的单位是焦耳(J)。
9. Ohm's Law and Resistance | 欧姆定律与电阻
Ohm' current in amperes (A) and resistance in ohms (Ω). The formula can be rearranged as I = V ÷ R or R = V ÷ I. Resistance limits the flow of charge.
欧姆定律描述了导体两端电压 V、通过它的电流 I 以及它的电阻 R 之间的关系：V = I × R。电压的单位是伏特(V)，电流的单位是安培(A)，电阻的单位是欧姆(Ω)。公式可变形为 I = V ÷ R 或 R = V ÷ I。电阻限制电荷的流动。
10. Series Circuits | 串联电路
In a series circuit, components are connected end to end, so there is only one path for the current. The current is the same through all components: Itotal = I1 = I2 = ... . The total voltage supplied by the battery is shared across the components: Vtotal = V1 + V2 + ... . The total resistance is the sum of individual resistances: Rtotal = R1 + R2 + ... .
在串联电路中，元件首尾相连，因此电流只有一条路径。通过所有元件的电流处处相等：I总 = I1 = I2 = ... 。电池提供的总电压在各元件上分配：V总 = V1 + V2 + ... 。总电阻等于各电阻之和：R总 = R1 + R2 + ... 。
11. Parallel Circuits | 并联电路
In a parallel circuit, components are connected on separate branches, offering multiple paths for current. The voltage across each branch is the same and equals the supply voltage: Vtotal = V1 = V2 = ... . The total current is the sum of the currents in the branches: Itotal = I1 + I2 + ... . For two resistors in parallel, the total resistance can be found using 1/Rtotal = 1/R1 + 1/R2.
在并联电路中，元件连接在独立的分支上，电流有多条路径。各支路两端电压相等且等于电源电压：V总 = V1 = V2 = ... 。总电流等于各支路电流之和：I总 = I1 + I2 + ... 。对于两个并联电阻，总电阻可利用 1/R总 = 1/R1 + 1/R2 计算。
12. Conservation of Energy | 能量守恒
Energy cannot be created or destroyed; it can only be transferred from one store to another, or dissipated (spread out) to the surroundings. In a closed system, the total energy remains constant. For example, when an object falls, gravitational potential energy is converted into kinetic energy, but the total mechanical energy stays the same (ignoring air resistance).
能量既不能被创造也不能被消灭；它只能从一个储存态转移到另一个储存态，或散失（耗散）到周围环境中。在一个封闭系统中，总能量保持不变。例如，物体下落时，重力势能转化为动能，但总机械能保持不变（忽略空气阻力时）。
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