📚 Year 8 Edexcel Physics: Quick Reference Handbook of Formulas and Principles | Year 8 Edexcel 物理：公式定理速查手册
This handbook brings together the essential formulas and key principles you will meet in Year 8 Edexcel Physics. Use it for quick revision, homework support and test preparation. Each section explains what the formula means, when to use it, and links the mathematical relationship to the physical world.
本手册汇总了 Year 8 Edexcel 物理课程中必须掌握的核心公式与重要定理。你可以用它进行快速复习、辅助作业和备考。每节都解释了公式的含义、适用条件，并把数学关系与实际物理世界联系起来。
1. Speed and Distance–Time Graphs | 速度与距离–时间图
Speed tells you how quickly an object covers distance. The formula is:
速度表示物体运动快慢的程度。公式为：
speed = distance ÷ time
or in symbols v = d / t rearrange the equation: distance = speed × time, and time = distance ÷ speed.
也可以用符号表示为 v = d / t。速度的单位可以是米每秒（m/s）或千米每小时（km/h）。已知三个量中的任意两个，就可以对公式进行变形：距离 = 速度 × 时间，时间 = 距离 ÷ 速度。
On a distance–time graph, a straight sloping line represents constant speed. The gradient of the line equals the speed. A horizontal line means the object is stationary.
在距离–时间图上，一条倾斜的直线表示匀速运动，直线的斜率等于速度。水平线表示物体静止不动。
2. Acceleration | 加速度
Acceleration describes how quickly velocity changes. It is not just 'speeding up'—it can also be slowing down (deceleration) or a change in direction.
加速度描述速度变化的快慢。它不仅仅是“加速”，也可以是减速或方向的改变。
acceleration = change in velocity ÷ time taken
In symbols: a = (v − u) / t, where v is final velocity, u is initial velocity and t is time. The unit is metre per second squared (m/s²).
符号表示为：a = (v − u) / t，其中 v 是末速度，u 是初速度，t 是时间。单位是米每二次方秒（m/s²）。
A positive value means the object is speeding up in the positive direction; a negative value (deceleration) means it is slowing down.
加速度为正表示物体在正方向上加速；负值（减速）表示物体在减速。
3. Newton’s Laws of Motion | 牛顿运动定律
Newton’s three laws are the foundation of force and motion.
牛顿三大定律是力与运动的基础。
First Law (Law of Inertia): An object remains at rest or moves in a straight line at constant speed unless acted on by an unbalanced force.
第一定律（惯性定律）： 除非受到非平衡力的作用，否则物体将保持静止或匀速直线运动状态。
Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The famous equation is:
第二定律： 物体的加速度与作用在其上的合力成正比，与物体的质量成反比。著名的公式为：
F = m × a
Force is measured in newtons (N), mass in kilograms (kg) and acceleration in m/s². For a given force, a larger mass gives a smaller acceleration.
力的单位是牛顿（N），质量单位是千克（kg），加速度单位是米每二次方秒（m/s²）。给定力的大小，质量越大，加速度越小。
Third Law: For every action force there is an equal and opposite reaction force. Forces always come in pairs acting on different objects.
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。力总是成对出现，并作用在不同物体上。
4. Weight and Gravity | 重力与重量
Weight is the force of gravity acting on an object’s mass. It is not the same as mass, which is a measure of the amount of matter.
重量是地球引力作用在物体质量上的力。它与质量不同，质量是物体所含物质的多少。
weight = mass × gravitational field strength
In symbols: W = m × g. Near the Earth’s surface, g is approximately 9.8 N/kg (often rounded to 10 N/kg for rough estimates). Weight is measured in newtons.
用符号表示为：W = m × g。在地球表面附近，g 大约是 9.8 N/kg（在粗略估算时常取 10 N/kg）。重量的单位是牛顿。
The mass of an object never changes with location, but its weight can change if g is different, such as on the Moon.
物体的质量不随地点改变，但如果 g 值不同（例如在月球上），重量会发生变化。
5. Density | 密度
Density links the mass of a substance to the volume it occupies. It tells you how tightly packed the particles are.
密度把物质的质量和它的体积联系起来，反映了粒子排列的紧密程度。
density = mass ÷ volume
In symbols: ρ = m / V and grams per cubic centimetre (g/cm³). Remember that 1 g/cm³ = 1000 kg/m³;.
用符号表示为：ρ = m / V。常用单位有千克每立方米（kg/m³）和克每立方厘米（g/cm³）。记住 1 g/cm³ = 1000 kg/m³;。
If an object has a density less than that of the fluid it is placed in, it will float; if its density is greater, it will sink.
若物体的密度小于所处流体的密度，物体会漂浮；若密度更大，则下沉。
6. Pressure and Moments | 压强与力矩
Pressure measures how concentrated a force is over an area. A small area gives a large pressure for the same force.
压强用来衡量力在面积上的集中程度。同样的力作用在更小的面积上会产生更大的压强。
pressure = force ÷ area
In symbols: P = F / A N/m². In liquids and gases, pressure increases with depth and acts in all directions.
符号公式为：P = F / A。单位是帕斯卡（Pa），1 Pa = 1 N/m²;。在液体和气体中，压强随深度增加而增大，并且向各个方向作用。
The moment of a force measures its turning effect. It depends on the size of the force and how far it is applied from the pivot.
力矩描述力的转动效果，它取决于力的大小和作用点到支点的垂直距离。
moment = force × perpendicular distance from pivot
The principle of moments: for an object to be balanced, the sum of clockwise moments must equal the sum of anticlockwise moments.
力矩原理：要使物体平衡，顺时针力矩之和必须等于逆时针力矩之和。
7. Work, Energy and Power | 功、能与功率
Work is done when a force moves an object through a distance. Energy is transferred during this process.
当力使物体移动一段距离时，我们就说力做了功，在这个过程中能量发生了转移。
work done = force × distance moved in the direction of the force
In symbols: W = F × d. Work is measured in joules (J). One joule is the work done when a force of 1 N moves an object 1 m.
符号表示为：W = F × d。功的单位是焦耳（J）。1 J 等于 1 N 的力使物体移动 1 m 所做的功。
Energy can be stored in different ways. Two common examples for Year 8 are kinetic energy and gravitational potential energy.
能量可以以不同的形式储存。Year 8 常见的两种是动能和重力势能。
kinetic energy (KE) = ½; × mass × speed²
gravitational potential energy (GPE) = mass × g × height
Power is the rate at which work is done or energy is transferred.
功率是做功或能量转移的速率。
power = work done ÷ time taken
or P = W / t (or P = E / t). The unit is watt (W); 1 W = 1 J/s.
或写作 P = W / t（也可用 P = E / t）。单位是瓦特（W），1 W = 1 J/s。
Efficiency shows how much of the input energy is converted to useful output. It is usually expressed as a percentage:
效率表明输入能量中有多少转化为有用的输出能量，通常用百分数表示：
efficiency = (useful output energy ÷ total input energy) × 100%
No device can be 100% efficient because some energy is always transferred to the thermal store of the surroundings.
没有设备可以达到 100% 的效率，因为总有一部分能量转移到周围环境的热能储存中。
8. Wave Properties | 波的性质
Waves transfer energy without transferring matter. The key quantities for any wave are frequency, wavelength and wave speed.
波能传递能量而不传递物质。任何波的关键物理量包括频率、波长和波速。
wave speed = frequency × wavelength
In symbols: v = f × λ. Frequency (f) is measured in hertz (Hz), wavelength (λ) in metres (m) and wave speed (v) in m/s.
用符号表示为：v = f × λ。频率 (f) 的单位是赫兹（Hz），波长 (λ) 的单位是米（m），波速 (v) 的单位是米每秒（m/s）。
You can identify a wave type by its direction of vibration. In transverse waves (e.g. light, water waves) vibrations are perpendicular to the direction of energy transfer. In longitudinal waves (e.g. sound), vibrations are parallel.
可以通过振动方向来辨别波的类型。横波（如光波、水波）的振动方向与能量传递方向垂直。纵波（如声波）的振动方向与能量传递方向平行。
The law of reflection states that the angle of incidence equals the angle of reflection, measured from the normal.
反射定律指出，入射角等于反射角，均从法线量起。
9. Electricity | 电学
An electric current is a flow of charge. In metals, this is a flow of electrons. The size of the current depends on the potential difference (voltage) and the resistance of the circuit.
电流是电荷的流动。金属导体中，电流是自由电子的流动。电流的大小取决于电路两端的电势差（电压）和电路的电阻。
potential difference = current × resistance
In symbols: V = I × R. Voltage (V) is measured in volts (V), current (I) in amperes (A) and resistance (R) in ohms (Ω).
符号公式为：V = I × R。电压 (V) 的单位是伏特（V），电流 (I) 的单位是安培（A），电阻 (R) 的单位是欧姆（Ω）。
There is also a relationship between charge, current and time:
电荷、电流和时间之间也有关系：
charge = current × time
or Q = I × t. Charge is measured in coulombs (C).
即 Q = I × t。电荷的单位是库仑（C）。
In series circuits, the current is the same everywhere, but the total resistance is the sum of individual resistances. In parallel circuits, the current splits, and the total resistance is less than the smallest individual resistance.
在串联电路中，各处电流相等，但总电阻等于各电阻之和。在并联电路中，电流会分流，总电阻小于最小的单个电阻。
10. Hooke’s Law and Elasticity | 胡克定律与弹性
When a spring is stretched, the extension is directly proportional to the applied force, provided the elastic limit is not exceeded.
在不超过弹性限度的情况下，弹簧的伸长量与施加的拉力成正比。
force = spring constant × extension
In symbols: F = k × x. Here k is the spring constant (N/m), which tells you how stiff the spring is, and x is the extension (m).
符号表示为：F = k × x。其中 k 是弹簧常数（单位 N/m），表示弹簧的刚度；x 是伸长量（单位 m）。
The straight-line graph of force against extension proves direct proportionality. Once the force is removed, an elastic object returns to its original length. If stretched beyond its elastic limit, the material deforms plastically and does not return to its original shape.
力与伸长量之间的直线图验证了正比关系。撤去外力后，弹性物体能恢复原长。如果拉伸超过弹性限度，材料就会发生塑性形变，无法恢复原状。
11. Energy Transfers and Conservation | 能量转移与守恒
The law of conservation of energy states that energy can never be created or destroyed; it can only be transferred from one store to another or from one form to another.
能量守恒定律指出，能量既不会凭空产生，也不会凭空消失，它只会从一个储存转移到另一个储存，或从一种形式转化为另一种形式。
There are eight main energy stores you should know: kinetic, gravitational potential, elastic potential, thermal, chemical, magnetic, electrostatic and nuclear. Energy can be transferred by four pathways: mechanically (by a force doing work), electrically (by an electric current), by heating and by radiation (light and sound).
你需要掌握八种主要的能量储存：动能、重力势能、弹性势能、热能、化学能、磁能、静电和核能。能量可以通过四种途径转移：机械做功（力做功）、电做功（电流）、加热以及辐射（光和声）。
In any closed system, the total energy before a change equals the total energy after. For example, when a ball is dropped, gravitational potential energy is converted to kinetic energy. When it hits the ground, some kinetic energy is transferred to thermal energy of the surroundings.
在任何封闭系统中，变化前的总能量等于变化后的总能量。例如，小球下落时，重力势能转化为动能；撞击地面时，部分动能转移到周围环境成为热能。
12. Gas Pressure and the Particle Model | 气体压强与粒子模型
The behaviour of solids, liquids and gases is explained by the particle model. In a gas, particles are in constant random motion and collide with the walls of the container, producing pressure.
粒子模型可以解释固体、液体和气体的行为。在气体中，粒子不停地做无规则运动，并与容器壁碰撞，从而产生压强。
If the temperature of a gas in a sealed container increases, the particles move faster and hit the walls harder and more often, so the pressure increases. If the volume of the container is decreased (with constant temperature), the particles hit the walls more frequently, also increasing pressure.
如果密封容器中的气体温度升高，粒子运动加快，撞击器壁更猛烈、更频繁，压强因此增大。如果减小容器的体积（在恒温条件下），粒子撞击器壁的频率升高，同样会导致压强增大。
le’s Law, more formally studied at a higher level but introduced here conceptually).
这些关系可概括为：一定质量的气体在温度不变时，压强与体积的乘积为定值（玻意耳定律，更高的年级将正式学习，这里作为概念引入）。
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