📚 Year 9 SQA Science: Formula & Theorem Quick Reference Handbook | 九年级 SQA 科学：公式定理速查手册
This handy reference handbook summarises the key formulas and theorems needed for Year 9 SQA Science. Whether you are studying physics, chemistry or biology, these equations and principles will support your revision and help you solve problems confidently.
这本便捷的速查手册总结了九年级 SQA 科学所需的关键公式和定理。无论你学习的是物理、化学还是生物，这些方程和原理都将助力你的复习，帮助你自信地解决问题。
1. Speed, Distance and Time | 速度、距离和时间
The speed of an object is the distance it travels per unit time. It can be calculated using the equation:
v = d / t
where v is speed (metres per second, m/s), d is distance (metres, m) and t is time (seconds, s). The formula can be rearranged to find distance d = v × t or time t = d / v.
物体的速度是单位时间内通过的距离，可用下式计算：
v = d / t
其中 v 是速度（米/秒，m/s），d 是距离（米，m），t 是时间（秒，s）。该公式可变形为求距离 d = v × t 或求时间 t = d / v。
2. Acceleration | 加速度
Acceleration is the rate of change of velocity. For uniform acceleration, we use:
a = (v - u) / t
where a is acceleration (m/s²), v is final velocity (m/s), u is initial velocity (m/s) and t is time (s). A positive result means speeding up; a negative result means slowing down.
加速度是速度变化的快慢。对于匀加速运动，我们使用：
a = (v - u) / t
其中 a 是加速度（m/s²），v 是末速度（m/s），u 是初速度（m/s），t 是时间（s）。正值表示加速，负值表示减速。
3. Newton's Second Law | 牛顿第二定律
The resultant force acting on an object equals its mass multiplied by its acceleration. This relationship is written as:
F = m × a
where F is the resultant force (newtons, N), m is mass (kilograms, kg) and a is acceleration (m/s²). The force and acceleration act in the same direction.
作用在物体上的合力等于物体的质量乘以其加速度。这一关系写作：
F = m × a
其中 F 是合力（牛顿，N），m 是质量（千克，kg），a 是加速度（m/s²）。力与加速度的方向相同。
4. Weight and Gravity | 重量和重力
Weight is the force of gravity acting on a mass. It is calculated with:
W = m × g
where W is weight (N), m is mass (kg) and g is gravitational field strength (N/kg). On Earth, g ≈ 9.8 N/kg, often rounded to 10 N/kg for simple problems.
重量是作用在质量上的重力，由下式计算：
W = m × g
其中 W 是重量（N），m 是质量（kg），g 是重力场强度（N/kg）。在地球上，g ≈ 9.8 N/kg，常简化为 10 N/kg 以方便计算。
5. Density | 密度
Density measures how much mass is packed into a given volume. The formula is:
ρ = m / V
where ρ (rho) is density (kg/m³), m is mass (kg) and V is volume (m³). An object floats if its density is less than the density of the fluid it is placed in.
密度测量的是单位体积内所含的质量，公式为：
ρ = m / V
其中 ρ（rho）是密度（kg/m³），m 是质量（kg），V 是体积（m³）。如果物体的密度小于其所在流体的密度，物体就会浮起。
6. Pressure | 压强
Pressure is the force exerted per unit area. It is given by:
P = F / A
where P is pressure (pascals, Pa or N/m²), F is force (N) and A is area (m²). A smaller contact area produces a larger pressure for the same force.
压强是单位面积上所受的压力，由下式给出：
P = F / A
其中 P 是压强（帕斯卡，Pa 或 N/m²），F 是力（N），A 是面积（m²）。在相同作用力下，接触面积越小，压强越大。
7. Ohm's Law | 欧姆定律
For many conductors, the current flowing through them is directly proportional to the potential difference across them, provided the temperature remains constant. This is Ohm's Law:
V = I × R
where V is voltage (volts, V), I is current (amperes, A) and R is resistance (ohms, Ω). The formula can be rearranged to find resistance R = V / I.
对于许多导体，在温度保持不变的情况下，通过导体的电流与导体两端的电压成正比。这就是欧姆定律：
V = I × R
其中 V 是电压（伏特，V），I 是电流（安培，A），R 是电阻（欧姆，Ω）。该公式可变形为求电阻 R = V / I。
8. Power and Energy | 功率和能量
Power is the rate at which energy is transferred or work is done. The equation linking power, energy and time is:
P = E / t
where P is power (watts, W), E is energy transferred (joules, J) and t is time (s). The total energy transferred can be found using E = P × t.
功率是能量传递或做功的速率。功率、能量和时间的关系式为：
P = E / t
其中 P 是功率（瓦特，W），E 是转移的能量（焦耳，J），t 是时间（s）。总能量转移可用 E = P × t 求得。
9. Wave Equation | 波动方程
The speed of a wave is related to its frequency and wavelength. For all waves, the wave equation is:
v = f × λ
where v is wave speed (m/s), f is frequency (hertz, Hz) and λ (lambda) is wavelength (m). This applies to sound waves, light waves and water waves.
波速与频率和波长相关。对所有波都适用的波动方程为：
v = f × λ
其中 v 是波速（m/s），f 是频率（赫兹，Hz），λ（lambda）是波长（m）。该方程适用于声波、光波和水波。
10. Photosynthesis | 光合作用
Photosynthesis is the process by which green plants use light energy to produce glucose from carbon dioxide and water. The overall chemical equation is:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Light energy is absorbed by chlorophyll to drive this reaction. Oxygen is released as a by-product.
光合作用是绿色植物利用光能将二氧化碳和水转化为葡萄糖的过程。总化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
叶绿素吸收光能驱动此反应，氧气作为副产物释放。
11. Respiration | 呼吸作用
Aerobic respiration is the reaction that releases energy from glucose in the presence of oxygen. The summary equation is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
This process occurs in the mitochondria of cells and provides the energy needed for life processes. Carbon dioxide and water are produced as waste products.
有氧呼吸是在有氧条件下从葡萄糖中释放能量的反应，总方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
该过程发生在细胞的线粒体中，为生命活动提供所需的能量。二氧化碳和水作为废物产生。
12. Conservation of Mass | 质量守恒
In a chemical reaction, the total mass of the reactants always equals the total mass of the products. No atoms are lost or gained; they are simply rearranged to form new substances. This principle is known as the conservation of mass.
在化学反应中，反应物的总质量总是等于生成物的总质量。原子既不会消失也不会增加，它们只是重新组合形成新的物质。这一原理被称为质量守恒定律。
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