📚 Year 9 AQA Physics: Formula & Theorem Quick Reference Handbook | Year 9 AQA 物理：公式定理速查手册
This quick‑reference handbook brings together the essential formulas, theorems and units from the Year 9 AQA Physics curriculum. Keep it handy when you are doing past‑paper questions, checking homework or brushing up on the basics before an end‑of‑topic test.
这本速查手册汇集了 Year 9 AQA 物理课程中的关键公式、定理和单位。在做历年真题、检查作业或在单元测验前巩固基础时，它可以随时为你提供帮助。
1. Speed | 速度
Speed describes how fast an object is moving. The average speed of an object can be calculated using the equation
v = s / t
where v is the speed in metres per second (m/s), s is the distance travelled in metres (m) and t is the time taken in seconds (s). This formula works only for uniform (steady) motion or when you need the average speed over a journey.
速度描述物体运动的快慢。物体的平均速度可用公式计算，其中 v 是速度（米/秒），s 是行驶距离（米），t 是所用时间（秒）。该公式仅适用于匀速运动或计算全程的平均速度。
2. Weight and Gravitational Field Strength | 重量与重力场强度
Weight is the force of gravity acting on an object. It is directly proportional to the object’s mass and can be found using
W = m g
where W is weight in newtons (N), m is mass in kilograms (kg) and g is the gravitational field strength in newtons per kilogram (N/kg). On Earth, g d in classroom calculations. Remember that mass stays the same everywhere, but weight changes with the strength of gravity.
重量是作用在物体上的重力。它与物体的质量成正比，可由公式求得。其中 W 是重量（牛顿），m 是质量（千克），g 是重力场强度（牛/千克）。在地球表面，g 约为 9.8 N/kg，课堂计算常取 10 N/kg。记住，质量处处相同，但重量会随重力强度而变。
3. Work Done (Energy Transfer) | 做功（能量转移）
Work is done whenever a force makes an object move. The amount of work done (which equals the energy transferred) is given by
W = F s
where W is work done in joules (J), F is the force applied in newtons (N) and s is the distance moved in the direction of the force in metres (m). One joule is the work done when a force of 1 N moves an object 1 m. If the force is not in the direction of motion, only the component along the motion does work.
只要力使物体移动，就做了功。做功的大小（等于转移的能量）由公式给出。其中 W 是做功（焦耳），F 是施加的力（牛顿），s 是沿力的方向移动的距离（米）。1 焦耳就是 1 牛顿的力使物体移动 1 米所做的功。如果力的方向与运动方向不一致，只有沿运动方向的分力才做功。
4. Kinetic Energy | 动能
Any moving object possesses kinetic energy. The kinetic energy depends on the object’s mass and speed:
KE = ½ m v²
where KE is kinetic energy in joules (J), m is mass in kilograms (kg) and v is speed in metres per second (m/s). Notice that doubling the speed quadruples the kinetic energy because velocity is squared.
任何运动的物体都具有动能。动能取决于物体的质量和速度。其中 KE 是动能（焦耳），m 是质量（千克），v 是速度（米/秒）。注意，速度加倍会使动能变为原来的四倍，因为速度是平方项。
5. Gravitational Potential Energy | 重力势能
An object lifted above the ground stores gravitational potential energy (GPE). The amount depends on its mass, height and the gravitational field strength:
GPE = m g h
where GPE is gravitational potential energy in joules (J), m is mass in kilograms (kg), g is gravitational field strength in N/kg and h is the change in height in metres (m). When an object falls, its GPE is converted into kinetic energy.
被举高的物体会储存重力势能。其大小取决于物体的质量、高度和重力场强度。其中 GPE 是重力势能（焦耳），m 是质量（千克），g 是重力场强度（牛/千克），h 是高度变化（米）。物体下落时，重力势能转化为动能。
6. Power | 功率
Power is the rate at which energy is transferred or work is done. It can be calculated in two equivalent ways:
P = W / t or P = ΔE / t
where P is power in watts (W), W is work done in joules (J), ΔE is energy transferred in joules (J) and t is time in seconds (s). One watt equals one joule per second. A powerful machine does the same amount of work in less time, or more work in the same time.
功率是能量转移或做功的快慢。它有两种等效的计算方式。其中 P 是功率（瓦特），W 是做功（焦耳），ΔE 是转移的能量（焦耳），t 是时间（秒）。1 瓦特等于 1 焦耳/秒。一台大功率的机器能用更短的时间做同样多的功，或者在相同时间内做更多的功。
7. Efficiency | 效率
No device is 100% efficient; some energy is always transferred to less useful stores (often thermal energy). Efficiency compares useful output energy to total input energy:
Efficiency = (useful output energy / total input energy) × 100%
ul power output and total power input can be used in the same way. A high efficiency means less energy is wasted.
任何设备都不可能 100% 高效；一部分能量总是会转移到用处不大的储存中（通常是热内能）。效率是有用输出能量与总输入能量之比。效率也可用小数表示（不乘 100）。有用输出功率与总输入功率的比值同样适用。效率高意味着能量浪费少。
8. Electrical Charge and Current | 电荷与电流
Electric current is a flow of charge. The size of the current depends on the amount of charge passing a point per second:
Q = I t
where Q is charge in coulombs (C), I is current in amperes (A) and t is time in seconds (s). This relationship is often used to calculate how long a battery can supply a given current or to find the charge transferred in a circuit.
电流是电荷的流动。电流的大小取决于每秒通过某点的电荷量。其中 Q 是电荷（库仑），I 是电流（安培），t 是时间（秒）。这个关系常用来计算电池能提供给定电流多长时间，或计算电路中转移的电荷量。
9. Ohm’s Law and Resistance | 欧姆定律与电阻
For an ohmic conductor at constant temperature, the current through it is directly proportional to the potential difference across it. This is summarised by
V = I R
where V is potential difference in volts (V), I is current in amperes (A) and R is resistance in ohms (Ω). The resistance tells you how difficult it is for current to flow. Components such as a fixed resistor follow Ohm’s Law, but non‑ohmic components (e.g. a filament lamp or diode) do not give a straight‑line I–V graph.
对于温度恒定的欧姆导体，通过它的电流与两端电压成正比。这概括为欧姆定律。其中 V 是电压（伏特），I 是电流（安培），R 是电阻（欧姆）。电阻反映了电流流动的难易程度。像定值电阻这样的元件遵守欧姆定律，而非欧姆元件（如灯丝灯泡或二极管）的 I–V 图不是一条直线。
10. Electrical Power and Energy | 电功率与电能
Electrical power tells you how quickly an appliance transfers energy. The two most useful formulas are
P = V I and P = I² R
where P is power in watts (W), V is potential difference in volts (V), I is current in amperes (A) and R is resistance in ohms (Ω). The first equation is general; the second applies when all the electrical power is converted to heat in a resistor. You can also calculate the energy transferred using E = P t, where energy is in joules (J) and time in seconds (s).
电功率表示用电器转移能量的快慢。最常用的两个公式是 P = V I 和 P = I² R。其中 P 是功率（瓦特），V 是电压（伏特），I 是电流（安培），R 是电阻（欧姆）。第一个公式是通用的；第二个适用于所有电功率都转化为热量（在电阻上）的情况。你还可以用 E = P t 计算转移的能量，能量单位是焦耳（J），时间单位是秒（s）。
11. Density | 密度
Density measures how much mass is packed into a given volume. It is a property of materials and does not depend on the size of the sample:
ρ = m / V
where ρ (Greek letter rho) is density in kilograms per cubic metre (kg/m³), m is mass in kilograms (kg) and V is volume in cubic metres (m³). Objects with a density lower than water (1000 kg/m³) float, while denser objects sink.
密度衡量单位体积内所含质量的大小。它是材料的一种属性，与样品大小无关。其中 ρ（希腊字母 rho）是密度（千克/立方米），m 是质量（千克），V 是体积（立方米）。密度低于水（1000 kg/m³）的物体上浮，密度更大的物体下沉。
12. Wave Speed | 波速
All waves (sound, water, light, etc.) obey the same wave‑speed equation:
v = f λ
where v is wave speed in metres per second (m/s), f is frequency in hertz (Hz) and λ (Greek lambda) is wavelength in metres (m). Frequency is the number of complete waves passing a point per second. For a fixed speed, a higher frequency results in a shorter wavelength.
所有波（声波、水波、光波等）都遵循相同的波速公式。其中 v 是波速（米/秒），f 是频率（赫兹），λ（希腊字母 lambda）是波长（米）。频率即每秒通过某点的完整波数目。波速固定时，频率越高，波长越短。
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