📚 Year 9 AQA Science: Quick Reference Handbook of Formulas and Theorems | 九年级AQA科学：公式定理速查手册
This handbook provides a quick reference to all the key formulas and theorems covered in Year 9 AQA Science, including Physics, Chemistry and Biology. Each entry is presented with clear notation, units and brief explanations to help you revise efficiently and build confidence before assessments.
本手册为Year 9 AQA科学课程中涵盖的所有关键公式和定理提供速查参考，包括物理、化学和生物。每个条目均配有清晰的符号、单位及简要解释，帮助你高效复习，在考试前树立信心。
1. Speed, Distance and Time | 速度、距离和时间
v = d ÷ t
Average speed (v, measured in m/s) is calculated by dividing the total distance travelled (d, in m) by the time taken (t, in s). The same equation can be rearranged to find distance (d = v × t) or time (t = d ÷ v).
平均速度（v，单位m/s）等于总移动距离（d，单位m）除以所用时间（t，单位s）。该公式可变形为距离（d = v × t）或时间（t = d ÷ v）。
2. Acceleration | 加速度
a = (v − u) ÷ t
Acceleration (a, in m/s²) is the change in velocity per unit time. Here u is the initial velocity (m/s), v is the final velocity (m/s), and t is the time taken (s). A negative value indicates deceleration.
加速度（a，单位m/s²）是单位时间内速度的变化量。u为初速度（m/s），v为末速度（m/s），t为时间（s）。负值表示减速。
3. Force, Mass and Acceleration | 力、质量和加速度
F = m × a
The resultant force (F, in newtons, N) acting on an object is equal to its mass (m, in kg) multiplied by its acceleration (a, in m/s²). This is Newton’s second law of motion, linking force, mass and acceleration.
作用在物体上的合力（F，单位牛顿N）等于物体的质量（m，单位kg）乘以其加速度（a，单位m/s²）。这是牛顿第二运动定律，将力、质量和加速度联系起来。
4. Weight and Gravitational Field Strength | 重量与引力场强度
W = m × g
Weight (W, in N) is the force due to gravity acting on a mass (m, in kg). On Earth the gravitational field strength (g) is approximately 9.8 N/kg (often taken as 10 N/kg). Weight varies on different planets, while mass stays the same.
重量（W，单位N）是由于重力作用在质量（m，单位kg）上的力。地球上的引力场强度（g）约9.8 N/kg（常取10 N/kg）。重量在不同行星上会变化，而质量保持不变。
5. Moments | 力矩
M = F × d
The moment of a force (M, in N m) is the turning effect about a pivot. It is calculated as the force (F, in N) multiplied by the perpendicular distance (d, in m) from the pivot to the line of action of the force. For equilibrium, total clockwise moments = total anticlockwise moments.
力矩（M，单位N m）是力绕支点的转动效应。它等于力（F，单位N）乘以从支点到力作用线的垂直距离（d，单位m）。平衡时，顺时针力矩总和等于逆时针力矩总和。
6. Pressure | 压强
p = F ÷ A
Pressure (p, in pascals, Pa, or N/m²) is the force (F, in N) acting per unit area (A, in m²). A smaller contact area produces a greater pressure for the same force, which explains why sharp objects cut more easily.
压强（p，单位帕斯卡Pa或N/m²）是单位面积（A，单位m²）上所作用的力（F，单位N）。相同力下，接触面积越小压强越大，这解释了锋利物体更易切割的原因。
7. Work, Energy and Power | 功、能量和功率
W = F × d
Work done (W, in joules, J) equals the force (F, in N) multiplied by the distance moved in the direction of the force (d, in m). When energy is transferred, work is done.
做功（W，单位焦耳J）等于力（F，单位N）乘以沿力的方向移动的距离（d，单位m）。能量转移时即做了功。
Eₖ = ½ m v²
Kinetic energy (Eₖ, in J) of a moving object depends on its mass (m, in kg) and the square of its velocity (v, in m/s). Doubling the speed quadruples the kinetic energy.
物体的动能（Eₖ，单位J）取决于质量（m，单位kg）和速度的平方（v，单位m/s）。速度加倍会使动能变为原来的四倍。
Eₚ = m g h
Gravitational potential energy (Eₚ, in J) gained or lost by an object is the product of its mass (m, in kg), gravitational field strength (g, in N/kg) and change in height (h, in m).
物体增加或减少的重力势能（Eₚ，单位J）是其质量（m，单位kg）、引力场强度（g，单位N/kg）和高度变化（h，单位m）的乘积。
P = W ÷ t
Power (P, in watts, W) is the rate of doing work or transferring energy. It is the work done (W, in J) divided by the time taken (t, in s). 1 watt = 1 joule per second.
功率（P，单位瓦特W）是做功或转移能量的速率。它等于做功（W，单位J）除以时间（t，单位s）。1瓦特表示每秒1焦耳。
8. Electrical Quantities | 电学量
Q = I × t
Electric charge (Q, in coulombs, C) transferred in a circuit equals current (I, in amperes, A) multiplied by time (t, in s).
电路中转移的电荷量（Q，单位库仑C）等于电流（I，单位安培A）乘以时间（t，单位s）。
V = I × R
Ohm’s law links potential difference (V, in volts, V), current (I, in A) and resistance (R, in ohms, Ω). For a fixed resistor, if V increases, I increases proportionally at constant temperature.
欧姆定律联系了电势差（V，单位伏特V）、电流（I，单位A）和电阻（R，单位欧姆Ω）。对于定值电阻，在温度恒定时，V增大I成比例增大。
P = I × V
Electrical power (P, in W) consumed by a component is the product of the current (I, in A) and the potential difference (V, in V). This can be combined with Ohm’s law to give P = I² R = V² / R.
用电器消耗的电功率（P，单位W）是电流（I，单位A）与电势差（V，单位V）的乘积。结合欧姆定律可得 P = I² R = V² / R。
E = P × t
Energy transferred (E, in J) equals power (P, in W) multiplied by time (t, in s). In electrical contexts, this can also be expressed as E = I V t.
转移的能量（E，单位J）等于功率（P，单位W）乘以时间（t，单位s）。在电学中也可写作 E = I V t。
9. Wave Speed | 波速
v = f × λ
The speed of a wave (v, in m/s) is the product of its frequency (f, in hertz, Hz) and its wavelength (λ, in m). This equation applies to all types of waves, including sound and light.
波速（v，单位m/s）等于波的频率（f，单位赫兹Hz）乘以波长（λ，单位m）。该公式适用于所有波，包括声波和光波。
10. Magnification | 放大倍率
M = eyepiece magnification × objective magnification
Total magnification (M) of a light microscope is found by multiplying the magnifying power of the eyepiece
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