📚 Year 8 Edexcel Physics Formula & Theorem Quick Reference Handbook | 八年级爱德思物理公式定理速查手册
This handbook provides a concise summary of the essential formulas and theorems needed for Year 8 Edexcel Physics. Use it for quick revision before tests and exams.
本手册简明总结了八年级爱德思物理所需的基本公式与定理。你可以用它进行考前快速复习。
1. Speed and Velocity | 速度与速率
Speed is the distance travelled per unit time. It is a scalar quantity, meaning it only has magnitude and no direction.
速度是单位时间内通过的距离。它是标量，只有大小，没有方向。
Velocity is speed in a given direction. It is a vector quantity, so it has both magnitude and direction.
速率是给定方向上的速度。它是矢量，既有大小也有方向。
The average speed of an object is calculated by dividing the total distance travelled by the total time taken.
物体的平均速度可通过总路程除以总时间来计算。
v = d / t
where v is speed, d is distance and t is time. The SI unit of speed is metre per second (m/s).
其中 v 代表速度，d 代表距离，t 代表时间。速度的国际单位是米每秒 (m/s)。
2. Acceleration | 加速度
Acceleration is the rate of change of velocity. It tells us how quickly an object speeds up, slows down or changes direction.
加速度是速度的变化率，它反映了物体加速、减速或改变方向的快慢。
If an object’s velocity increases, the acceleration is positive; if the velocity decreases, the acceleration is negative (often called deceleration).
若速度增大，加速度为正；若速度减小，加速度为负（常称为减速度）。
a = Δv / t
where a is acceleration, Δv is change in velocity (final velocity − initial velocity) and t is the time taken. The unit is m/s².
其中 a 是加速度，Δv 是速度变化量（末速度 − 初速度），t 是时间。单位是米每二次方秒 (m/s²)。
3. Newton’s Laws of Motion | 牛顿运动定律
First Law (Law of Inertia): An object remains at rest or moves with constant velocity unless acted upon by an external resultant force.
第一定律（惯性定律）： 任何物体都将保持静止或匀速直线运动状态，直到有外力迫使其改变。
Second Law: The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. This leads to the most important equation of motion:
第二定律： 物体的加速度与它所受的合外力成正比，与它的质量成反比。由此得出最重要的运动方程：
F = m × a
where F is the resultant force in newtons (N), m is mass in kilograms (kg) and a is acceleration in m/s².
其中 F 是合外力（单位牛顿 N），m 是质量（单位千克 kg），a 是加速度（单位 m/s²）。
Third Law: For every action force there is an equal and opposite reaction force.
第三定律： 每一个作用力总有一个大小相等、方向相反的反作用力。
4. Weight and Mass | 重力与质量
Mass is the amount of matter in an object and is measured in kilograms (kg). It does not change with location.
质量是物体所含物质的多少，用千克 (kg) 衡量，不随位置改变。
Weight is the gravitational force acting on an object. It depends on the mass of the object and the gravitational field strength (g).
重量是作用在物体上的重力，它取决于物体的质量和重力场强度 (g)。
W = m × g
Weight is measured in newtons (N). On Earth, g ≈ 10 N/kg, so an object of mass 1 kg weighs approximately 10 N.
重量以牛顿 (N) 为单位。在地球上，g ≈ 10 N/kg，因此质量为 1 kg 的物体重约 10 N。
5. Work, Energy and Power | 功、能量与功率
Work is done when a force moves an object in the direction of the force. It is a form of energy transfer.
当力使物体沿力的方向移动时，力做了功，功是能量传递的一种形式。
W = F × d
where W is work done in joules (J), F is force in newtons (N) and d is distance moved in metres (m).
其中 W 是功（单位焦耳 J），F 是力（N），d 是沿力方向移动的距离（m）。
Gravitational potential energy (GPE) is the energy an object has due to its height above the ground.
重力势能是物体因被举高而具有的能量。
GPE = m × g × h
where h is the change in height. Kinetic energy (KE) is the energy an object possesses because of its motion.
其中 h 是高度变化。动能是物体由于运动而具有的能量。
KE = ½ m v²
Power is the rate at which work is done or energy is transferred.
功率是做功或能量转化的快慢。
P = W / t
Power is measured in watts (W), where 1 W = 1 J/s.
功率的单位是瓦特 (W)，1 W = 1 J/s。
6. Conservation of Energy | 能量守恒定律
Energy cannot be created or destroyed; it can only be transferred, stored or dissipated (spread out to the surroundings). The total energy in a closed system remains constant.
能量既不会凭空产生，也不会凭空消失，它只会从一种形式转化为另一种形式，或从一个物体转移到其他物体，而在转化或转移的过程中，总量保持不变。
In most real-world situations, some energy is always dissipated as heat due to friction or air resistance, but the total energy is still conserved.
在现实情况下，摩擦力或空气阻力常会使部分能量以热的形式耗散，但总能量依然守恒。
This principle is used to solve problems involving energy changes, for instance when a falling object converts GPE to KE (ignoring air resistance):
该原理用于解决能量转化问题，例如物体下落时重力势能转化为动能（忽略空气阻力）：
m g h = ½ m v²
7. Density | 密度
Density is the mass per unit volume of a substance. It tells us how tightly packed the particles are.
密度是单位体积内所含的质量，它反映了物质微粒排列的紧密程度。
ρ = m / V
where ρ (Greek letter rho) is density in kg/m³, m is mass in kg and V is volume in m³. A solid block’s volume is length × width × height.
其中 ρ（希腊字母 rho）是密度 (kg/m³)，m 是质量 (kg)，V 是体积 (m³)。规则固体的体积 = 长 × 宽 × 高。
Objects with a density less than water (1000 kg/m³) float; those with greater density sink.
密度小于水 (1000 kg/m³) 的物体会上浮；密度大于水的物体下沉。
8. Pressure | 压强
Pressure is the force applied perpendicular to a surface per unit area. The same force can produce different pressures depending on the area over which it acts.
压强是垂直作用在物体单位面积上的力。相同的力，作用面积不同，产生的压强也不同。
p = F / A
where p is pressure in pascals (Pa), F is force in newtons (N) and A is area in square metres (m²). Note that 1 Pa = 1 N/m².
其中 p 是压强 (Pa)，F 是压力 (N)，A 是受力面积 (m²)。注意 1 Pa = 1 N/m²。
A large area reduces pressure (e.g., snowshoes), while a small area increases pressure (e.g., a sharp knife).
增大受力面积可以减小压强（如滑雪板），减小受力面积可以增大压强（如锋利的刀）。
9. Electric Current, Voltage and Ohm’s Law | 电流、电压与欧姆定律
Electric current is the rate of flow of electric charge. It is measured in amperes (A) using an ammeter connected in series.
电流是电荷定向移动的速率，单位为安培 (A)，用串联的电流表测量。
I = Q / t
where I is current, Q is charge (coulombs, C) and t is time (s).
其中 I 是电流，Q 是电荷量 (库仑 C)，t 是时间 (s)。
Voltage (potential difference) is the energy transferred per unit charge. It is measured in volts (V) using a voltmeter in parallel.
电压（电位差）是单位电荷转移的能量，单位为伏特 (V)，用并联的电压表测量。
Ohm’s Law states that the current through a resistor is directly proportional to the potential difference across it, provided the temperature remains constant.
欧姆定律指出：在温度不变时，通过导体的电流与导体两端的电压成正比。
V = I × R
where V is voltage (V), I is current (A) and R is resistance in ohms (Ω).
其中 V 是电压 (V)，I 是电流 (A)，R 是电阻 (Ω)。
10. Wave Properties | 波的性质
All waves transfer energy without transferring matter. The wave speed depends on the frequency and wavelength.
所有波都能传递能量而不传递物质。波速取决于频率和波长。
v = f × λ
where v is wave speed (m/s), f is frequency in hertz (Hz) and λ (lambda) is wavelength in metres (m).
其中 v 是波速 (m/s)，f 是频率 (Hz)，λ (lambda) 是波长 (m)。
Frequency is the number of complete waves passing a point per second. The period T is the time for one complete wave: T = 1 / f.
频率是每秒通过某点的完整波数目。周期 T 是一个完整波所需的时间：T = 1 / f。
The Law of Reflection applies to light, sound and water waves. It states that the angle of incidence equals the angle of reflection, measured from the normal (the imaginary line perpendicular to the surface).
反射定律适用于光波、声波和水波。它指出入射角等于反射角，两者都是从法线（垂直于界面的假想线）量起。
θᵢ = θᵣ
where θᵢ is the angle of incidence and θᵣ is the angle of reflection.
其中 θᵢ 是入射角，θᵣ 是反射角。
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