📚 Year 7 AQA Physics: Formula and Theorem Quick Reference Handbook | Year 7 AQA 物理：公式定理速查手册
This quick reference handbook covers all the key formulas and theorems you will learn in Year 7 AQA Physics. Mastering these equations is essential for solving problems and understanding physical concepts. Each section includes the formula, explanation of symbols, units and a brief worked example to help you apply the ideas.
本速查手册涵盖了 Year 7 AQA 物理课程中所有重要的公式和定理。掌握这些方程是解决问题和理解物理概念的关键。每个小节都包含公式、符号解释、单位和简要例题，帮助你应用这些知识。
1. Speed | 速度
Speed tells us how fast an object is moving. It is a scalar quantity, which means it only has magnitude and no direction. You can calculate the average speed of an object if you know how far it has travelled and how long it took.
速度表示物体运动的快慢。它是一个标量，只有大小，没有方向。只要知道物体运动的距离和所用的时间，就可以计算出它的平均速度。
speed = distance ÷ time
v = d ÷ t
Distance (d) is measured in metres (m).
距离(d)的单位是米(m)。
Time (t) is measured in seconds (s).
时间(t)的单位是秒(s)。
Therefore speed (v) is measured in metres per second (m/s).
因此速度(v)的单位是米每秒(m/s)。
Example: A cyclist travels 150 m in 30 s. The speed is 150 ÷ 30 = 5 m/s.
例题：一名自行车手在30秒内骑行了150米。速度为 150 ÷ 30 = 5 米/秒。
2. Weight and Gravity | 重力与引力
Weight is the force acting on an object due to gravity. It is not the same as mass. Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is a force and is measured in newtons (N).
重量是由于万有引力作用在物体上的力。它与质量不同。质量是物体所含物质的多少，单位是千克(kg)。重量是一种力，单位是牛顿(N)。
weight = mass × gravitational field strength
W = m × g
On Earth, the gravitational field strength (g) is approximately 9.8 N/kg. For Year 7 calculations, we often round this to 10 N/kg to make the maths easier.
在地球上，引力场强度(g)约为 9.8 N/kg。在 Year 7 的计算中，我们通常将其四舍五入为 10 N/kg，以便简化计算。
Example: A book has a mass of 2 kg. Its weight on Earth is 2 × 10 = 20 N.
例题：一本书质量为 2千克。它在地球上的重量为 2 × 10 = 20 牛。
3. Hooke's Law | 胡克定律
Hooke's Law describes the behaviour of springs. When a spring is stretched, the extension (increase in length) is directly proportional to the force applied, provided the elastic limit is not exceeded.
胡克定律描述了弹簧的行为。当弹簧被拉伸时，只要不超过弹性限度，伸长量（增加的长度）与施加的力成正比。
force = spring constant × extension
F = k × e
F is the force applied in newtons (N).
F 是施加的力，单位是牛顿(N)。
k is the spring constant in newtons per metre (N/m).
k 是弹簧常数，单位是牛每米(N/m)。
e is the extension in metres (m).
e 是伸长量，单位是米(m)。
of 50 N/m. A force of 10 N is applied. The extension will be e = F ÷ k = 10 ÷ 50 = 0.2 m.
例题：一根弹簧的弹簧常数为 50 N/m。施加了 10 N 的力。伸长量为 e = F ÷ k = 10 ÷ 50 = 0.2 米。
4. Density | 密度
Density is a measure of how much mass is packed into a certain volume. Objects made of the same material have the same density, regardless of their size or shape.
密度是衡量单位体积内包含多少质量的物理量。由相同材料制成的物体，无论大小或形状如何，密度都相同。
density = mass ÷ volume
ρ = m ÷ V
The Greek letter ρ (rho) is used for density.
希腊字母 ρ (rho) 用来表示密度。
Mass (m) is in kilograms (kg) and volume (V) is in cubic metres (m³).
质量(m)的单位是千克(kg)，体积(V)的单位是立方米(m³)。
Density is therefore measured in kilograms per cubic metre (kg/m³).
因此密度的单位是千克每立方米(kg/m³)。
um has a mass of 2.7 kg and a volume of 0.001 m³. Its density is 2.7 ÷ 0.001 = 2700 kg/m³.
例题：一块铝的质量为 2.7 千克，体积为 0.001 立方米。它的密度为 2.7 ÷ 0.001 = 2700 kg/m³。
5. Pressure | 压强
Pressure tells us how concentrated a force is over an area. A sharp knife exerts a high pressure because the force is spread over a very small area.
压强表示力在面积上的集中程度。锋利的刀之所以能产生很大的压强，是因为力分布在一个非常小的面积上。
pressure = force ÷ area
P = F ÷ A
Force (F) is in newtons (N) and area (A) is in square metres (m²).
力(F)的单位是牛顿(N)，面积(A)的单位是平方米(m²)。
Pressure (P) is measured in pascals (Pa). 1 Pa = 1 N/m².
压强(P)的单位是帕斯卡(Pa)。1 Pa = 1 N/m²。
Example: A force of 500 N acts on an area of 0.1 m². The pressure is 500 ÷ 0.1 = 5000 Pa.
例题：一个 500 N 的力作用在 0.1 m² 的面积上。压强为 500 ÷ 0.1 = 5000 Pa。
6. Work Done | 做功
Work is done whenever a force moves an object. Energy is transferred from one store to another when work is done.
只要一个力使物体移动，就做了功。做功时，能量从一个储存库转移到另一个储存库。
work done = force × distance moved in the direction of the force
W = F × d
Work (W) is measured in joules (J). Force (F) is in newtons (N). Distance (d) is in metres (m).
功(W)的单位是焦耳(J)。力(F)的单位是牛顿(N)。距离(d)的单位是米(m)。
1 joule is the work done when a force of 1 newton moves an object 1 metre in the direction of the force.
1 焦耳就是 1 牛顿的力使物体沿力的方向移动 1 米所做的功。
pushes a trolley with a force of 20 N over a distance of 5 m. Work done = 20 × 5 = 100 J.
例题：一个人用 20 N 的力推一辆手推车，移动了 5 米。做功 = 20 × 5 = 100 J。
7. Gravitational Potential Energy | 重力势能
Gravitational potential energy (GPE) is the energy an object has because of its position in a gravitational field. The higher the object, the more GPE it has.
重力势能(GPE)是物体由于其处于引力场中的位置而具有的能量。物体位置越高，重力势能越大。
change in GPE = mass × gravitational field strength × change in height
ΔEₚ = m × g × Δh
Mass (m) is in kg, g is in N/kg, and height (h) is in metres (m).
质量(m)的单位是千克，g 的单位是 N/kg，高度(h)的单位是米(m)。
GPE is measured in joules (J).
重力势能的单位是焦耳(J)。
.2 kg is lifted 3 m upwards. Using g = 10 N/kg, the increase in GPE is 0.2 × 10 × 3 = 6 J.
例题：一个质量为 0.2 千克的球被举高 3 米。取 g = 10 N/kg，重力势能的增加量为 0.2 × 10 × 3 = 6 J。
8. Power | 功率
Power is the rate at which work is done or energy is transferred. A more powerful machine does the same amount of work in less time.
功率是做功或能量转移的速率。一台功率更大的机器，完成相同的功所需的时间更短。
power = work done ÷ time taken
P = W ÷ t
Power (P) is measured in watts (W), where 1 watt equals 1 joule per second (J/s).
功率(P)的单位是瓦特(W)，1 瓦特等于 1 焦耳每秒(J/s)。
xample: A motor lifts a weight, doing 600 J of work in 20 s. The power is 600 ÷ 20 = 30 W.
例题：一台电动机提升重物，在 20 秒内做了 600 J 的功。功率为 600 ÷ 20 = 30 W。
9. Ohm's Law | 欧姆定律
Ohm's Law links voltage, current and resistance in an electrical circuit. For a given resistor at constant temperature, the current through it is directly proportional to the voltage across it.
欧姆定律将电路中的电压、电流和电阻联系在一起。对于给定电阻，在温度不变的情况下，通过它的电流与两端的电压成正比。
voltage = current × resistance
V = I × R
Voltage (V) is measured in volts (V).
电压(V)的单位是伏特(V)。
Current (I) is measured in amperes or amps (A).
电流(I)的单位是安培(A)。
Resistance (R) is measured in ohms (Ω).
电阻(R)的单位是欧姆(Ω)。
of 15 Ω and a current of 0.4 A flows through it. The voltage across it is 0.4 × 15 = 6 V.
例题：一个元件的电阻为 15 Ω，通过它的电流为 0.4 A。它两端的电压为 0.4 × 15 = 6 V。
10. Wave Speed | 波速
Waves transfer energy from one place to another. The speed of a wave depends on its frequency and wavelength.
波将能量从一个地方传递到另一个地方。波速取决于它的频率和波长。
wave speed = frequency × wavelength
v = f × λ
Wave speed (v) is in metres per second (m/s).
波速(v)的单位是米每秒(m/s)。
Frequency (f) is the number of waves per second, measured in hertz (Hz).
频率(f)是每秒产生的波的个数，单位是赫兹(Hz)。
Wavelength (λ) is the distance between two corresponding points on a wave, measured in metres (m).
波长(λ)是波上两个对应点之间的距离，单位是米(m)。
e has a frequency of 440 Hz and a wavelength of 0.78 m. Its speed is 440 × 0.78 ≈ 343 m/s.
例题：一个声波的频率为 440 Hz，波长为 0.78 m。它的波速为 440 × 0.78 ≈ 343 m/s。
11. Moments | 力矩
The moment of a force is a measure of its turning effect. It depends on the size of the force and the perpendicular distance from the pivot to the line of action of the force.
力矩衡量一个力的转动效果。它取决于力的大小以及支点到力作用线的垂直距离。
moment = force × perpendicular distance from pivot
M = F × d
Moment (M) is measured in newton metres (Nm).
力矩(M)的单位是牛米(Nm)。
The principle of moments states that for an object to be balanced, the total clockwise moment must equal the total anticlockwise moment about the same pivot.
力矩原理指出，要使物体平衡，对同一支点的顺时针力矩之和必须等于逆时针力矩之和。
Example: A force of 4 N is applied 0.3 m from a pivot. The moment is 4 × 0.3 = 1.2 Nm.
例题：在距离支点 0.3 米处施加一个 4 N 的力。力矩为 4 × 0.3 = 1.2 Nm。
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) as thermal energy. The total energy before a change is always equal to the total energy afterwards.
能量不能被创造或毁灭。它只能从一个储存库转移到另一个储存库，或者以热能的形式散失（扩散）。发生变化之前的总能量总是等于之后的总能量。
Total energy before = Total energy after
Etotal (before) = Etotal (after)
This theorem is useful when analysing energy changes, such as a falling object where gravitational potential energy is converted into kinetic energy (ignoring air resistance).
这个定理在分析能量变化时非常有用，例如下落的物体中，重力势能转化为动能（忽略空气阻力）。
In real situations, some energy is always transferred to the thermal store of the surroundings because of friction or air resistance.
在实际情况中，由于摩擦或空气阻力，总有一部分能量转移到周围环境的热能储存库中。
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