📚 Year 8 CCEA Physics: Quick Reference Formula & Theorem Handbook | Year 8 CCEA 物理：公式定理速查手册
This handbook brings together the essential formulae and theorems you will meet in Year 8 CCEA Physics. Use it to revise key relationships, units and the ideas behind them.
这本手册汇集了 Year 8 CCEA 物理课程中所有的核心公式与定理。你可以用它来回顾重要的关系式、单位以及它们背后的概念。
1. Speed, Distance and Time | 速度、距离与时间
Speed tells you how fast an object is moving. Average speed is the total distance travelled divided by the total time taken.
速度告诉你物体运动的快慢。平均速度等于通过的总距离除以所用的总时间。
v = d / t
Where v = average speed (m/s), d = distance (m), t = time (s).
其中 v = 平均速度（米/秒），d = 距离（米），t = 时间（秒）。
| speed | v | metres per second (m/s) |
| distance | d | metres (m) |
| time | t | seconds (s) |
To calculate distance, rearrange the formula: d = v × t. To find time, use t = d / v.
要计算距离，变形公式：d = v × t。计算时间，用 t = d / v。
2. Acceleration | 加速度
Acceleration is the rate of change of velocity. An object accelerates when its speed or direction changes.
加速度是速度变化的快慢。当物体的速度大小或方向改变时，它就在加速。
a = (v - u) / t
cceleration (m/s²), v = final velocity (m/s), u = initial velocity (m/s) and t = time (s).
式中 a = 加速度（米/秒²），v = 末速度（米/秒），u = 初速度（米/秒），t = 时间（秒）。
If the value is negative, it is deceleration (slowing down).
如果算出的值小于零，表示减速。
3. Forces and Newton's Laws | 力与牛顿定律
Newton’s Second Law describes how an unbalanced force causes an object to accelerate. The acceleration is directly proportional to the force and inversely proportional to the mass.
牛顿第二定律描述不平衡力如何使物体加速。加速度与力成正比，与物体质量成反比。
F = m × a
F = resultant force (newtons, N), m = mass (kg), a = acceleration (m/s²).
F = 合力（牛顿），m = 质量（千克），a = 加速度（米/秒²）。
Newton’s First Law: an object remains at rest or moves at constant speed in a straight line unless a resultant force acts on it.
牛顿第一定律：如果没有合力作用，物体将保持静止或匀速直线运动状态。
Newton’s Third Law: for every action force there is an equal and opposite reaction force.
牛顿第三定律：每一个作用力都有一个大小相等、方向相反的反作用力。
4. Weight and Mass | 重量与质量
Weight is the force due to gravity acting on a mass. Mass is the amount of matter in an object and does not change with location.
重量是地球引力作用于物体上的力。质量是物体所含物质的多少，不随地点改变。
W = m × g
weight (N), m = mass (kg), g = gravitational field strength (N/kg). On Earth g ≈ 10 N/kg.
W = 重量（牛），m = 质量（千克），g = 引力场强度（牛/千克）。地球上 g ≈ 10 N/kg。
Do not confuse weight and mass: weight is a force, measured in newtons; mass is a scalar, measured in kilograms.
不要把重量和质量混淆：重量是力，单位是牛顿；质量是标量，单位是千克。
5. Pressure | 压强
Pressure is a measure of how concentrated a force is. It tells you how much force acts on a given area.
压强衡量力的集中程度。它反映单位面积上受力的大小。
p = F / A
p = pressure (pascals, Pa), F = force (N), A = area (m²). 1 Pa = 1 N/m².
p = 压强（帕斯卡），F = 力（牛），A = 面积（米²）。1 Pa = 1 N/m²。
A sharp knife cuts easily because the small area produces high pressure. Snowshoes prevent sinking by increasing the area and reducing pressure.
锋利的刀容易切割，因为面积小导致压强大。雪鞋通过增大面积减小压强，防止下陷。
6. Moments | 力矩
A moment is the turning effect of a force about a pivot. It depends on the size of the force and the distance from the pivot.
力矩是力使物体绕支点转动的效果。它取决于力的大小和力到支点的垂直距离。
M = F × d
M = moment (newton metres, N m), F = force (N), d = perpendicular distance from pivot (m).
M = 力矩（牛·米），F = 力（牛），d = 到支点的垂直距离（米）。
oments: for an object in equilibrium, total clockwise moment = total anticlockwise moment.
力矩原理：物体平衡时，顺时针力矩之和等于逆时针力矩之和。
7. Energy and Work | 能量与功
Work is done when a force moves an object in the direction of the force. Energy is the ability to do work; both are measured in joules.
当力使物体沿力的方向移动时，力做了功。能是做功的本领；功和能的单位都是焦耳。
W = F × d
W = work done (J), F = force (N), d = distance moved in direction of force (m).
W = 做功（焦），F = 力（牛），d = 物体在力方向上移动的距离（米）。
Energy can be stored as kinetic, gravitational potential, elastic, thermal, chemical or nuclear energy. Energy is always conserved: it cannot be created or destroyed, only transferred.
能量可以储存为动能、重力势能、弹性势能、热能、化学能或核能。能量总是守恒的：既不能创造，也不能消灭，只能转移。
8. Power | 功率
Power is the rate of doing work or the rate of energy transfer. A more powerful machine transfers energy more quickly.
功率是做功的快慢，或者能量转移的速率。功率越大的机器，传递能量越快。
P = W / t
P = power (watts, W), W = work done or energy transferred (J), t = time (s).
P = 功率（瓦特），W = 做功或转移的能量（焦），t = 时间（秒）。
1 watt is 1 joule per second.
1 瓦特等于每秒 1 焦耳。
9. Electrical Quantities | 电量
Electric current is the rate of flow of charge. Charge is measured in coulombs, current in amperes and time in seconds.
电流是电荷流动的速率。电荷的单位是库仑，电流的单位是安培，时间单位是秒。
Q = I × t
Q = charge (C), I = current (A), t = time (s).
Q = 电荷量（库），I = 电流（安），t = 时间（秒）。
Potential difference (voltage) is the energy transferred per unit charge: V = W / Q.
电势差（电压）是每单位电荷转移的能量：V = W / Q。
10. Ohm's Law | 欧姆定律
Ohm’s Law links voltage, current and resistance for a metallic conductor at constant temperature.
欧姆定律描述了在温度不变时，金属导体两端电压、电流和电阻之间的关系。
V = I × R
V = voltage (V), I = current (A), R = resistance (Ω).
V = 电压（伏），I = 电流（安），R = 电阻（欧）。
Resistance is the opposition to current flow. A higher resistance reduces the current for a given voltage.
电阻是对电流的阻碍作用。在电压一定时，电阻越大，电流越小。
11. Waves: Speed, Frequency and Wavelength | 波：速度、频率与波长
All waves obey the wave equation. This relationship links the speed of a wave, its frequency and its wavelength.
所有波都遵从波动方程。这个关系式把波速、频率和波长联系在一起。
v = f × λ
λ = wavelength (m). Frequency is the number of complete waves passing a point per second.
v = 波速（米/秒），f = 频率（赫兹），λ = 波长（米）。频率是每秒通过某点的完整波的个数。
light waves, the speed in vacuum is 3.0 × 10⁸ m/s. For sound in air, it is about 340 m/s.
光在真空中的波速是 3.0 × 10⁸ m/s，声音在空气中的波速大约是 340 m/s。
12. Density | 密度
Density is the mass per unit volume of a substance. It tells you how tightly packed the matter is.
密度是单位体积的质量。它反映物质排列的紧密程度。
ρ = m / V
ρ = density (kg/m³), m = mass (kg), V = volume (m³).
ρ = 密度（千克/米³），m = 质量（千克），V = 体积（米³）。
Objects with a density less than water (1000 kg/m³) float; those with a greater density sink.
密度小于水（1000 kg/m³）的物体浮起，密度大于水的物体下沉。
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