KS3 Edexcel Physics: Formula and Theorems Quick Reference Handbook | KS3 Edexcel 物理：公式定理速查手册

📚 KS3 Edexcel Physics: Formula and Theorems Quick Reference Handbook | KS3 Edexcel 物理：公式定理速查手册

This quick reference handbook gathers the essential formulas and theorems you will encounter in KS3 Edexcel Physics. Understanding these relationships will help you describe motion, forces, energy, electricity, waves and matter with confidence. Each equation is presented with practical context, unit guidance and tips for applying it to real problems.

本速查手册汇集了 KS3 Edexcel 物理课程中的核心公式和定理。掌握这些关系式将帮助你自信地描述运动、力、能量、电学、波以及物质。每个公式都配有实际情景、单位指南和解题小提示。

1. Speed, Distance and Time | 速度、距离和时间

v = d / t

Speed is the distance an object travels in a certain time. To calculate average speed, divide the total distance by the total time taken. The standard unit of speed is metres per second (m/s).

速度是物体在某段时间内移动的距离。要计算平均速度，用总距离除以所用的总时间。速度的标准单位是米每秒 (m/s)。

In a distance-time graph, the gradient of the line represents speed. A steeper slope indicates faster motion; a horizontal line means the object is stationary.

在距离-时间图中，线的斜率代表速度。斜率越大表示运动越快；水平线表示物体静止。

If a cyclist covers 300 m in 20 s, her speed is v = 300 m ÷ 20 s = 15 m/s. To convert 72 km/h to m/s, divide by 3.6, giving 20 m/s.

若一名自行车手在 20 s 内骑行了 300 m，她的速度为 v = 300 m ÷ 20 s = 15 m/s。要将 72 km/h 换算为 m/s，除以 3.6，得到 20 m/s。

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2. Acceleration | 加速度

a = (v − u) / t

Acceleration tells us how quickly speed changes. It is the change in velocity per unit time. If the final speed v is greater than the initial speed u, acceleration is positive; if v is smaller, the object decelerates (negative acceleration).

加速度描述了速度变化快慢，是单位时间内速度的变化量。如果末速度 v 大于初速度 u，加速度为正；若 v 小于 u，物体做减速运动（负加速度）。

The unit of acceleration is metres per second squared (m/s²). A car that speeds up from 10 m/s to 30 m/s in 5 s has an acceleration of a = (30 − 10) / 5 = 4 m/s².

加速度的单位是米每二次方秒 (m/s²)。一辆汽车在 5 s 内从 10 m/s 加速到 30 m/s，其加速度为 a = (30 − 10) / 5 = 4 m/s²。

On a velocity-time graph, the gradient gives acceleration. A straight, sloping line means constant acceleration, while a horizontal line shows constant velocity and zero acceleration.

在速度-时间图中，斜率表示加速度。一条倾斜直线表示匀加速，水平直线表示匀速运动、加速度为零。

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3. Weight and Mass | 重量和质量

W = m × g

Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity acting on that mass, measured in newtons (N). The gravitational field strength on Earth, g, is approximately 10 N/kg.

质量是物体所含物质的多少，单位是千克 (kg)。重量是作用在质量上的重力，单位是牛顿 (N)。地球表面的引力场强度 g 约为 10 N/kg。

Weight depends on the gravitational field strength, so an object’s weight is different on the Moon, where g is only about 1.6 N/kg, while its mass remains unchanged.

重量取决于引力场强度，因此同一物体在月球上的重量不同，月球上的 g 大约只有 1.6 N/kg，而物体的质量保持不变。

Use a Newton meter to measure weight directly. Never confuse mass and weight: mass is scalar and weight is a vector that acts towards the centre of the Earth.

用弹簧秤可以直接测量重量。永远不要混淆质量和重量：质量是标量，而重量是方向指向地心的矢量。

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4. Density | 密度

ρ = m / V

Density is the mass per unit volume of a substance. It is measured in kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). 1 g/cm³ = 1000 kg/m³.

密度是物质单位体积的质量，单位是千克每立方米 (kg/m³) 或克每立方厘米 (g/cm³)。1 g/cm³ = 1000 kg/m³。

To find the density of an irregular solid, measure its mass with a balance and its volume by water displacement in a measuring cylinder. Then divide mass by volume.

要测量不规则固体的密度，先用天平测出质量，再用排水法用量筒测出体积，然后用质量除以体积。

Objects with lower density than a fluid will float; those with higher density sink. Understanding density helps to explain why some materials are used for buoyancy aids or shipbuilding.

密度小于流体的物体会上浮，密度大于流体的会下沉。理解密度有助于解释为什么某些材料用于浮力装置或造船。

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5. Pressure | 压强

P = F / A

Pressure is the force per unit area applied to a surface. The unit of pressure is the pascal (Pa), where 1 Pa = 1 N/m².

压强是作用在单位面积上的力。压强单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。

For a given force, decreasing the area increases the pressure. A sharp knife has a very small edge area, so it exerts high pressure and cuts easily. Flat shoes spread weight over a larger area, reducing pressure on soft ground.

在力一定的情况下，面积越小压强越大。锋利的刀刃面积非常小，因此能产生较大的压强，容易切割。平底鞋把重量分散到较大面积，降低了松软地面上的压强。

Pressure in a liquid depends on depth and density, but the basic P = F / A equation is used whenever a concentrated force acts on a surface.

液体压强与深度和密度有关，但只要力集中作用于表面，就可以使用 P = F / A 这一基本公式。

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6. Work Done | 做功

W = F × d

Work is done when a force moves an object in the direction of the force. Work is a measure of energy transfer and is measured in joules (J). 1 joule is the work done when a force of 1 newton moves an object 1 metre.

当力使物体沿力的方向移动时，我们说力做了功。功是能量转移的量度，单位是焦耳 (J)。1 焦耳即 1 牛顿的力使物体移动 1 米所做的功。

If the force and movement are not in the same direction, only the component of force in the direction of motion contributes to work done.

如果力和移动方向不在同一直线上，只有沿运动方向的分力才做功。

Lifting a book of weight 5 N onto a shelf 2 m high requires work W = 5 N × 2 m = 10 J. This energy is stored as gravitational potential energy.

将一本重 5 N 的书举到 2 m 高的书架上需要做功 W = 5 N × 2 m = 10 J。这部分能量转化为重力势能储存起来。

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7. Power | 功率

P = W / t

Power is the rate at which work is done or energy is transferred. The unit of power is the watt (W), where 1 W = 1 J/s.

功率是做功或能量转移的快慢，单位是瓦特 (W)，1 W = 1 J/s。

A machine that performs a large amount of work in a short time has high power. If two identical loads are lifted to the same height, the one lifted faster requires more power even though the work done is the same.

在短时间内做大量功的机器功率较高。若将两个相同重物提升到相同高度，提升较快的一台需要更大功率，尽管做的功相同。

A 60 W light bulb transfers 60 J of electrical energy into light and heat every second. Energy transferred can also be found from E = P × t, which links power and time.

一个 60 W 的灯泡每秒钟将 60 J 电能转化为光能和热能。转移的总能量也可通过 E = P × t 求得，该式把功率和时间联系起来。

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8. Ohm’s Law | 欧姆定律

V = I × R

Ohm’s Law states that the current through a conductor is directly proportional to the potential difference across it, provided temperature remains constant. Voltage V is measured in volts (V), current I in amperes (A) and resistance R in ohms (Ω).

欧姆定律指出，在温度不变的条件下，通过导体的电流与导体两端的电势差成正比。电压 V 的单位是伏特 (V)，电流 I 的单位是安培 (A)，电阻 R 的单位是欧姆 (Ω)。

A component that obeys Ohm’s Law has a constant resistance, and its current-voltage graph is a straight line passing through the origin. Resistors, especially metal wires, behave like this at constant temperature.

遵从欧姆定律的元件具有恒定电阻，其电流-电压图是一条通过原点的直线。金属导线等电阻器在恒温下即表现出此特性。

If a 12 V battery pushes a current of 3 A through a resistor, its resistance is R = V / I = 12 V ÷ 3 A = 4 Ω. Adding resistors in series increases total resistance; adding them in parallel decreases it.

如果一节 12 V 电池使 3 A 电流通过一个电阻器，其电阻为 R = V / I = 12 V ÷ 3 A = 4 Ω。串联电阻会增大总电阻，并联电阻会减小总电阻。

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9. Electrical Power | 电功率

P = I × V

Electrical power can be calculated by multiplying current and voltage. In circuits, power is also given by P = I²R or P = V² / R when resistance is known. The unit remains the watt (W).

电功率可以通过电流与电压相乘计算。在电路中，若已知电阻，还可使用 P = I²R 或 P = V² / R 计算。单位仍是瓦特 (W)。

Different forms of the power equation are useful when only some quantities are known. For a device with a fixed resistance, doubling the voltage quadruples the power dissipated because P ∝ V².

不同形式的功率公式在仅知道部分物理量时很有用。对于电阻固定的装置，电压加倍会使消耗的功率变为四倍，因为 P ∝ V²。

Energy transferred by an electrical appliance can be found using E = P × t. This is how electricity meters measure energy in kilowatt-hours (kWh), though in physics we often use joules.

用电器转移的能量可通过 E = P × t 计算。这正是电表以千瓦时 (kWh) 计量能量的原理，但在物理中我们更常用焦耳。

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10. Wave Speed Equation | 波速方程

v = f × λ

The wave speed equation links the speed of a wave (v, in m/s) to its frequency (f, in hertz, Hz) and wavelength (λ, in metres). Frequency is the number of complete waves passing a point per second.

波速方程将波速 (v, 单位 m/s)、频率 (f, 单位赫兹 Hz) 和波长 (λ, 单位米) 联系起来。频率是每秒通过某点的完整波的数目。

For all electromagnetic waves travelling in a vacuum, v is equal to the speed of light, about 300 000 000 m/s (3 × 10⁸ m/s). This means higher frequency waves have shorter wavelengths.

所有在真空中传播的电磁波，v 都等于光速，约为 300 000 000 m/s (3 × 10⁸ m/s)。这意味着频率越高的波，其波长越短。

Use the wave equation to rearrange for frequency or wavelength. For instance, a sound wave of frequency 500 Hz and wavelength 0.68 m has speed v = 500 Hz × 0.68 m = 340 m/s.

利用波方程可以求频率或波长。例如，一个频率 500 Hz、波长 0.68 m 的声波，其波速为 v = 500 Hz × 0.68 m = 340 m/s。

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11. Moments | 力矩

M = F × d

Moment is the turning effect of a force about a pivot. It is calculated by multiplying the force by the perpendicular distance from the pivot to the line of action of the force. The unit is newton metre (N m).

力矩是力对支点产生的转动效果。计算力矩时，用力乘以支点到力作用线的垂直距离。单位是牛顿米 (N m)。

The principle of moments states that for an object in rotational equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments. This is used to find unknown forces or distances in levers and seesaws.

力矩原理指出，当物体处于转动平衡时，顺时针力矩之和等于逆时针力矩之和。这用于计算杠杆和跷跷板中未知的力或距离。

To increase a moment, either apply a larger force or increase the distance from the pivot. That is why a spanner with a long handle makes it easier to loosen a tight nut.

要增大力矩，可以增大作用力或增加离支点的距离。这就是为什么长柄扳手更容易拧松紧螺母。

A balanced seesaw with a 300 N person sitting 2 m from the pivot can be balanced by a 400 N person sitting at 1.5 m on the other side, because 300 N × 2 m = 600 N m and 400 N × 1.5 m = 600 N m.

一架平衡的跷跷板，若一侧有一个重 300 N 的人坐在离支点 2 m 处，另一侧可由重 400 N 的人坐在 1.5 m 处维持平衡，因为 300 N × 2 m = 600 N m，而 400 N × 1.5 m = 600 N m。

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