📚 SQA Year 7 Physics: Formula & Theorem Quick-Reference Handbook | SQA 七年级物理：公式定理速查手册
Welcome to your Year 7 SQA Physics Quick-Reference Handbook. This guide brings together all the key formulas and theorems you need for your physics course, clearly explained in both English and Chinese to support bilingual learning. Use it to revise, check your understanding, and build confidence before tests.
欢迎使用七年级 SQA 物理公式定理速查手册。本手册汇集了物理课程所需的所有关键公式和定理，并用中英双语清晰解释，以辅助双语学习。你可以用它进行复习、检查理解，并在考试前建立信心。
1. Speed, Distance and Time | 速度、距离与时间
v = d / t
Speed (v) is the distance (d) travelled divided by the time (t) taken. The standard units are metres per second (m/s) for speed, metres (m) for distance and seconds (s) for time. You can rearrange the formula to find distance: d = v × t or time: t = d / v.
速度 (v) 等于通过的距离 (d) 除以所用的时间 (t)。标准单位是速度用米/秒 (m/s)，距离用米 (m)，时间用秒 (s)。公式可变形为求距离：d = v × t 或求时间：t = d / v。
2. Density | 密度
ρ = m / V
Density (ρ, the Greek letter rho) is mass (m) per unit volume (V). It is usually measured in kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). To find the mass, use m = ρ × V; to find the volume, use V = m / ρ.
密度 (ρ, 希腊字母 rho) 是每单位体积 (V) 的质量 (m)。常用单位是千克/立方米 (kg/m³) 或克/立方厘米 (g/cm³)。求质量用 m = ρ × V；求体积用 V = m / ρ。
3. Weight and Mass | 重量与质量
W = m × g
Weight (W) is the force due to gravity acting on an object. It is equal to the mass (m) multiplied by the gravitational field strength (g). On Earth, g = 9.8 N/kg, often approximated as 10 N/kg. Weight is measured in newtons (N), mass in kilograms (kg).
重量 (W) 是由于重力作用在物体上的力。它等于质量 (m) 乘以引力场强度 (g)。在地球上，g = 9.8 N/kg，通常可取 10 N/kg 近似。重量单位是牛顿 (N)，质量单位是千克 (kg)。
4. Hooke’s Law | 胡克定律
F = k × x
Hooke’s Law states that the force (F) needed to extend or compress a spring is directly proportional to the extension or compression (x), as long as the elastic limit is not exceeded. k is the spring constant (N/m). The formula is F = k × x. Beyond the elastic limit, the spring deforms permanently.
胡克定律指出，在未超过弹性限度时，拉伸或压缩弹簧所需的力 (F) 与伸长量或压缩量 (x) 成正比。k 是弹簧常数 (N/m)。公式为 F = k × x。超过弹性限度后，弹簧将发生永久变形。
5. Pressure | 压强
P = F / A
Pressure (P) is the force (F) acting per unit area (A). It is measured in pascals (Pa), where 1 Pa = 1 N/m². This relationship shows that a given force produces higher pressure when applied over a smaller area.
压强 (P) 是作用在单位面积 (A) 上的力 (F)。单位为帕斯卡 (Pa)，其中 1 Pa = 1 N/m²。该关系表明，在较小面积上施加给定力时，产生的压强更大。
6. Work Done | 做功
W = F × d
Work (W) is done when a force (F) moves an object through a distance (d) in the direction of the force. Work is measured in joules (J). If the force is perpendicular to the motion, no work is done on the object.
当力 (F) 使物体沿力的方向移动一段距离 (d) 时，就做了功 (W)。功的单位是焦耳 (J)。如果力的方向与运动方向垂直，则不做功。
7. Power | 功率
P = E / t
Power (P) is the rate at which energy is transferred or work is done. It equals the energy (E) or work transferred divided by the time (t) taken. Power is measured in watts (W), where 1 W = 1 J/s.
功率 (P) 是能量传递或做功的速率。它等于传递的能量 (E) 或功除以所用的时间 (t)。功率单位是瓦特 (W)，1 W = 1 J/s。
8. Ohm’s Law | 欧姆定律
V = I × R
Ohm’s Law relates voltage (V), current (I) and resistance (R) in a conductor: V = I × R. Voltage is in volts (V), current in amperes (A) and resistance in ohms (Ω). This law holds for ohmic conductors at constant temperature.
欧姆定律描述了导体中电压 (V)、电流 (I) 和电阻 (R) 的关系：V = I × R。电压的单位是伏特 (V)，电流是安培 (A)，电阻是欧姆 (Ω)。该定律适用于温度恒定的欧姆导体。
9. Wave Speed | 波速
v = f × λ
The speed of a wave (v) is the product of its frequency (f) and wavelength (λ, lambda). Frequency is the number of waves per second (hertz, Hz), and wavelength is the distance between two consecutive crests (metres, m). This equation applies to all types of waves, including sound and light.
波速 (v) 是波的频率 (f) 与波长 (λ, lambda) 的乘积。频率是每秒波的数量 (赫兹, Hz)，波长是连续两个波峰间的距离 (米, m)。该方程适用于所有类型的波，包括声波和光波。
10. Efficiency | 效率
η = (Useful output / Total input) × 100%
Efficiency (η, eta) measures how much of the total energy input is converted into useful output. It is calculated as useful output energy (or power) divided by total input energy (or power), multiplied by 100%. No device can be 100% efficient due to energy losses, usually as heat.
效率 (η, eta) 衡量总输入能量有多少转换为有用输出。计算为有用输出能量 (或功率) 除以总输入能量 (或功率)，再乘以 100%。由于存在能量损耗 (通常以热量形式)，任何设备的效率都不可能达到 100%。
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