📚 Year 8 OCR Physics: Formula & Theorem Quick Reference Handbook | Year 8 OCR 物理：公式定理速查手册
This quick reference handbook gathers every essential formula and theorem from the Year 8 OCR Physics syllabus. Whether you are revising for an end‑of‑topic test or building a solid foundation for GCSE, use these clear statements, symbol meanings and worked examples to check your understanding and boost your confidence.
这本速查手册汇总了 Year 8 OCR 物理课程中所有核心公式与定理。无论你是在准备单元测验，还是为 GCSE 打基础，都可以利用这些清晰的表述、符号说明和计算示例来检验理解、增强信心。
1. Speed, Distance and Time | 速度、距离与时间
The speed of an object is the distance it travels per unit of time. The relationship is fundamental for interpreting motion graphs and solving distance–time problems.
物体的速度是单位时间内移动的距离。这个关系是解读运动图像、解决距离-时间问题的基础。
v = d / t
v is speed (metres per second, m/s), d is distance (metres, m), t is time (seconds, s). Always convert minutes or hours into seconds before using the formula.
v 是速度（米/秒，m/s），d 是距离（米，m），t 是时间（秒，s）。使用前务必将分钟或小时换算成秒。
Example: A runner completes 300 m in 25 s. Using v = 300 m ÷ 25 s gives a speed of 12 m/s.
示例：一名跑者 25 秒跑完 300 米。v = 300 m ÷ 25 s，速度为 12 m/s。
2. Force, Mass and Acceleration | 力、质量与加速度
Newton’s Second Law describes how an unbalanced force causes an object to accelerate. The size of the acceleration depends on the mass of the object and the net force acting on it.
牛顿第二定律描述了不平衡力如何使物体产生加速度。加速度的大小取决于物体的质量和作用在其上的合力。
F = m a
F is the resultant force (newtons, N), m is the mass (kilograms, kg), a is the acceleration (metres per second squared, m/s²). The acceleration is in the same direction as the net force.
F 是合力（牛顿，N），m 是质量（千克，kg），a 是加速度（米/秒²，m/s²）。加速度方向与合力方向一致。
If a 2 kg trolley is pushed with a resultant force of 10 N, its acceleration is a = F / m = 10 N ÷ 2 kg = 5 m/s².
如果用 10 N 的合力推动一辆 2 kg 的小车，加速度 a = F/m = 10 N ÷ 2 kg = 5 m/s²。
3. Weight and Gravitational Field Strength | 重量与重力场强度
Weight is the force of gravity acting on a mass. It is not the same as mass; weight changes with the strength of the gravitational field.
重量是重力作用在质量上的力。它与质量不同；重量随重力场强度的变化而改变。
W = m g
W is weight (N), m is mass (kg), g is gravitational field strength (N/kg). On Earth, g ≈ 9.8 N/kg (often rounded to 10 N/kg in calculations).
W 是重量（N），m 是质量（kg），g 是重力场强度（N/kg）。地球表面 g ≈ 9.8 N/kg（计算中通常近似为 10 N/kg）。
A 5 kg object on Earth has a weight of W = 5 kg × 10 N/kg = 50 N.
地球上质量为 5 kg 的物体，重量 W = 5 kg × 10 N/kg = 50 N。
4. Pressure | 压强
Pressure measures how concentrated a force is over an area. A larger area reduces pressure, while a smaller area increases it for the same force.
压强衡量力在面积上的集中程度。相同力下，面积越大压强越小，面积越小压强越大。
P = F / A
P is pressure (pascals, Pa, or N/m²), F is the force applied perpendicular to the surface (N), A is the area over which the force is spread (m²).
P 是压强（帕斯卡，Pa，即 N/m²），F 是垂直作用于表面的力（N），A 是力分布的面积（m²）。
If a 600 N force acts on an area of 0.3 m², the pressure is P = 600 N ÷ 0.3 m² = 2000 Pa.
若 600 N 的力作用在 0.3 m² 的面积上，压强 P = 600 N ÷ 0.3 m² = 2000 Pa。
5. Moments (Turning Effect) | 力矩（转动效应）
A moment is the turning effect produced by a force about a pivot. The size of the moment depends on both the force and its perpendicular distance from the pivot.
力矩是力对支点产生的转动效应。力矩的大小取决于力和力到支点的垂直距离。
M = F × d (perpendicular)
M is moment (newton‑metres, N m), F is the force (N), d is the perpendicular distance from the pivot to the line of action of the force (m).
M 是力矩（牛顿·米，N m），F 是力（N），d 是支点到力的作用线的垂直距离（m）。
The principle of moments states that for an object in equilibrium, total clockwise moment = total anticlockwise moment about the same pivot.
力矩原理指出：当物体平衡时，顺时针方向的总力矩等于逆时针方向的总力矩。
6. Work, Energy and Power | 功、能量和功率
Work is done when a force moves an object in the direction of the force. Energy is transferred mechanically when work is done.
当力使物体沿力的方向移动时，就做了功。做功时能量通过机械方式转移。
W = F × s
W is work done (joules, J), F is the force (N), s is the distance moved in the direction of the force (m). Work and energy share the same unit.
W 是功（焦耳，J），F 是力（N），s 是沿力方向移动的距离（m）。功和能量使用相同单位。
Gravitational potential energy gained by an object raised through a height h is GPE = m g h, where m is mass (kg), g is gravitational field strength (N/kg).
物体被举高 h 后增加的重力势能 GPE = m g h，m 为质量（kg），g 为重力场强度（N/kg）。
The kinetic energy of a moving object is KE = ½ m v², where v is speed (m/s). Energy is conserved; it is never created or destroyed, only transferred or stored.
运动物体的动能 KE = ½ m v²，v 为速度（m/s）。能量守恒，既不会创生也不会消灭，只会转移或储存。
Power is the rate of doing work or transferring energy: P = W / t, where t is time (s). Power is measured in watts (W), where 1 W = 1 J/s.
功率是做功或转移能量的快慢：P = W / t，t 为时间（s）。功率单位为瓦特（W），1 W = 1 J/s。
7. Electrical Circuits – Ohm’s Law | 电路 – 欧姆定律
Ohm’s Law links current, voltage and resistance in a conductor kept at a constant temperature. It allows you to predict one quantity when the other two are known.
欧姆定律将恒温导体中的电流、电压和电阻联系在一起。知道其中两个量，就能算出第三个。
V = I R
V is potential difference (volts, V), I is current (amperes, A), R is resistance (ohms, Ω). Resistance tells you how much the component opposes the flow of current.
V 是电势差（伏特，V），I 是电流（安培，A），R 是电阻（欧姆，Ω）。电阻表示元件对电流的阻碍程度。
For a lamp with a current of 0.5 A and a resistance of 8 Ω, the required voltage is V = 0.5 A × 8 Ω = 4 V.
一个电阻为 8 Ω 的灯泡，通过 0.5 A 电流时，电压 V = 0.5 A × 8 Ω = 4 V。
In a series circuit, total resistance is the sum of individual resistances: R_total = R₁ + R₂ + … . In parallel circuits, the total resistance is less than the smallest individual resistance.
串联电路中，总电阻等于各个电阻之和：R_total = R₁ + R₂ + … 。并联电路的总电阻小于最小的单个电阻。
8. Electrical Power | 电功率
Electrical power tells you the rate at which an appliance transfers electrical energy. The formula combines the two key electrical quantities, current and voltage.
电功率表示用电器转移电能的快慢。该公式结合了电流和电压这两个关键电学量。
P = I V
P is power (W), I is current (A), V is potential difference (V). For any component, energy transferred E = P × t = I V t.
P 是功率（W），I 是电流（A），V 是电势差（V）。对任何元件，转移的电能 E = P × t = I V t。
If a heater draws 4 A from a 230 V supply, its power is P = 4 A × 230 V = 920 W. In one minute (60 s), it transfers 920 W × 60 s = 55 200 J of energy.
若一个加热器从 230 V 电源取用 4 A 电流，功率 P = 4 A × 230 V = 920 W。一分钟（60 s）内它转移的电能为 920 W × 60 s = 55 200 J。
9. Density | 密度
Density is a property that tells you how much mass is packed into a given volume. It explains why some objects float while others sink.
密度是反映单位体积内所含质量的属性。它解释了为什么有些物体会漂浮，有些则会下沉。
ρ = m / V
ρ (Greek letter rho) is density (kg/m³ or g/cm³), m is mass (kg or g), V is volume (m³ or cm³). Be careful to match the units; 1 g/cm³ = 1000 kg/m³.
ρ（希腊字母 rho）是密度（kg/m³ 或 g/cm³），m 是质量（kg 或 g），V 是体积（m³ 或 cm³）。注意单位统一：1 g/cm³ = 1000 kg/m³。
A stone of mass 150 g occupies a volume of 50 cm³, so its density is ρ = 150 g ÷ 50 cm³ = 3 g/cm³, equivalent to 3000 kg/m³.
一块质量 150 g、体积 50 cm³ 的石头，密度 ρ = 150 g ÷ 50 cm³ = 3 g/cm³，相当于 3000 kg/m³。
10. Wave Speed | 波速
All waves transfer energy from one place to another without transferring matter. The speed of a wave depends on the medium and can be found from its frequency and wavelength.
所有波都能将能量从一处传递到另一处而不转移物质。波速取决于介质，可由频率和波长求出。
v = f λ
v is wave speed (m/s), f is frequency (hertz, Hz), λ (lambda) is wavelength (m). Frequency is the number of complete waves passing a point per second.
v 是波速（m/s），f 是频率（赫兹，Hz），λ（lambda）是波长（m）。频率是每秒通过某点的完整波数。
A sound wave in air has a frequency of 440 Hz and a wavelength of 0.78 m. Its speed is v = 440 Hz × 0.78 m = 343.2 m/s, which is close to the typical speed of sound.
空气中一个频率为 440 Hz、波长为 0.78 m 的声波，波速 v = 440 Hz × 0.78 m = 343.2 m/s，接近典型声速。
11. Hooke’s Law | 胡克定律
Hooke’s Law describes the behaviour of springs and many elastic materials when they are stretched, as long as the elastic limit is not exceeded.
胡克定律描述了弹簧和许多弹性材料在拉伸时的特性，前提是未超过弹性限度。
F = k e
F is the applied force (N), e is the extension (change in length, m), k is the spring constant (N/m), a measure of the stiffness of the spring. The extension is directly proportional to the force.
F 是施加的力（N），e 是伸长量（长度变化，m），k 是弹簧常数（N/m），表征弹簧的刚度。伸长量与力成正比。
If a spring extends by 0.05 m when a 10 N weight is hung on it, the spring constant is k = F / e = 10 N ÷ 0.05 m = 200 N/m.
若一个弹簧在悬挂 10 N 重物时伸长 0.05 m，其弹簧常数 k = F/e = 10 N ÷ 0.05 m = 200 N/m。
12. Law of Reflection | 反射定律
When light strikes a smooth surface, it obeys the law of reflection. This law governs how mirrors form images and is central to ray‑diagram constructions.
当光线射到光滑表面时，遵循反射定律。该定律决定了平面镜成像，也是光路图作图的核心。
∠i = ∠r
The angle of incidence (i) is the angle between the incident ray and the normal (the line perpendicular to the surface). The angle of reflection (r) is between the reflected ray and the normal. Both angles are measured from the normal, not from the surface.
入射角（i）是入射光线与法线（垂直于表面的线）之间的夹角。反射角（r）是反射光线与法线之间的夹角。两个角都是从法线量起，而非从表面量。
The incident ray, reflected ray and normal all lie in the same plane. This simple rule is the basis for understanding periscopes, mirrors and light paths.
入射光线、反射
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