📚 Year 9 Edexcel Physics Formula & Theorem Quick Reference | Year 9 Edexcel 物理公式定理速查手册
This quick reference guide gathers the essential formulas, principles, and key relationships you need to master for Year 9 Edexcel Physics. Each entry is explained with core ideas and accompanied by a Chinese translation to support dual-language learning. Use it for revision, homework, and exam preparation.
本速查手册汇集了 Year 9 Edexcel 物理课程中必须掌握的核心公式、定理和关键关系。每个条目都配有核心解释和中文翻译，助力双语学习。适用于复习、作业与备考。
1. Speed, Distance and Time | 速度、路程与时间
Average speed is defined as the total distance travelled divided by the total time taken. The formula links these three quantities and can be rearranged to find distance or time when the other two are known. Speed is a scalar; it has magnitude only.
平均速度的定义是总路程除以总时间。这个公式将三个量联系起来，当已知其中两个量时，可以变形求出第三个量。速度是标量，只有大小。
speed = distance ÷ time v = s / t
- v = speed (m/s)
- s = distance (m)
- t = time (s)
When motion is in a straight line and at a constant speed, the distance–time graph is a straight line. The gradient (slope) of a distance–time graph gives the speed.
当物体沿直线做匀速运动时，路程–时间图像是一条直线。路程–时间图像的斜率（坡度）表示速度。
For a journey with varying speed, the average speed is still calculated by total distance over total time, even if the graph is curved.
对于速度变化的行程，即便图像是曲线，平均速度仍由总路程除以总时间求得。
2. Acceleration | 加速度
Acceleration describes how quickly the velocity of an object changes. It is a vector quantity, so it has both magnitude and direction. An object accelerates if it speeds up, slows down (deceleration) or changes direction.
加速度描述物体速度变化的快慢。它是矢量，既有大小又有方向。物体加速、减速或改变方向时都有加速度。
acceleration = change in velocity ÷ time taken a = (v – u) / t
- a = acceleration (m/s²)
- v = final velocity (m/s)
- u = initial velocity (m/s)
- t = time (s)
On a velocity–time graph, the gradient gives the acceleration. A straight line indicates constant acceleration. The area under the graph represents the distance travelled.
在速度–时间图像中，斜率表示加速度。直线表示匀加速。图像下方的面积表示物体的位移/路程。
If the velocity–time graph slopes downwards, the acceleration is negative, meaning the object is decelerating.
如果速度–时间图像向下倾斜，加速度为负，说明物体在减速。
3. Forces and Newton's Laws | 力与牛顿定律
Forces are pushes or pulls that can change the shape, speed or direction of an object. The unit of force is the newton (N). Forces can be contact (e.g. friction) or non-contact (e.g. gravity, magnetic).
力是推或拉，可以改变物体的形状、速度或方向。力的单位是牛顿（N）。力可分为接触力（如摩擦力）和非接触力（如重力、磁力）。
Newton's First Law (Law of Inertia): An object remains at rest or moves with constant velocity unless acted on by a resultant force.
牛顿第一定律（惯性定律）： 除非受到合外力作用，物体将保持静止或匀速直线运动状态。
Newton's Second Law: The acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass.
牛顿第二定律： 物体的加速度与合外力成正比，与物体的质量成反比。
resultant force = mass × acceleration F = m a
- F = resultant force (N)
- m = mass (kg)
- a = acceleration (m/s²)
Newton's Third Law: For every action force there is an equal and opposite reaction force. These forces act on different objects.
牛顿第三定律： 每一个作用力都有一个大小相等、方向相反的反作用力。这两个力作用在不同物体上。
4. Weight, Mass and Gravity | 重量、质量与重力
Weight is the force acting on an object due to gravity. It is not the same as mass, which is the amount of matter in an object. Mass is measured in kilograms (kg) and is the same everywhere; weight is measured in newtons (N) and depends on the gravitational field strength.
重量是重力作用在物体上的力。它与质量不同，质量是物体所含物质的多少。质量以千克（kg）为单位，在任何地方都相同；重量以牛顿（N）为单位，取决于引力场强度。
weight = mass × gravitational field strength W = m g
- W = weight (N)
- m = mass (kg)
- g field strength (N/kg). On Earth, g ≈ 9.8 N/kg (often rounded to 10 N/kg for calculations).
The gravitational field strength on the Moon is about 1.6 N/kg, so an object's weight is much smaller there, but its mass remains unchanged.
月球的引力场强度约为 1.6 N/kg，因此物体在月球上的重量小很多，但质量保持不变。
Weight is a force, so it is a vector quantity and always acts towards the centre of the planet.
重量是一种力，因此是矢量，方向总是指向行星中心。
5. Work Done and Energy Transfer | 做功与能量转移
When a force moves an object, work is done. Work done measures the energy transferred by the force. It is a scalar quantity measured in joules (J). One joule is the work done when a force of one newton moves an object one metre in the direction of the force.
当一个力使物体移动时，就做了功。功衡量力所传递的能量，是标量，单位是焦耳（J）。1 焦耳是 1 牛顿的力使物体沿力的方向移动 1 米所做的功。
work done = force × distance moved in direction of force W = F d
- W = work done (J)
- F = force (N)
- d = distance moved (m)
The distance must be measured parallel to the force. If the force is perpendicular to the movement, no work is done.
距离必须沿力的方向测量。如果力与运动方向垂直，则不做功。
Work done is equal to the energy transferred. For example, lifting a book against gravity does work and increases the book's gravitational potential energy.
做功等于转移的能量。例如，将书向上提升克服重力做功，增加了书的重力势能。
6. Gravitational Potential Energy and Kinetic Energy | 重力势能与动能
Energy exists in different forms. Two important mechanical forms are gravitational potential energy (GPE) and kinetic energy (KE). GPE is the energy stored in an object because of its height above the ground. KE is the energy an object has due to its motion.
能量以不同形式存在。两种重要的机械能形式是重力势能（GPE）和动能（KE）。GPE 是物体由于离地高度而储存的能量。KE 是物体由于运动而具有的能量。
GPE = mass × gravitational field strength × height Eₚ = m g h
- Eₚ = gravitational potential energy (J)
- m = mass (kg)
- g = gravitational field strength (N/kg or m/s²)
- h = height (m)
KE = ½ × mass × velocity² Eₖ = ½ m v²
- Eₖ = kinetic energy (J)
- m = mass (kg)
- v = velocity (m/s)
In many situations, energy converts between GPE and KE. If air resistance is negligible, the sum of GPE and KE remains constant (conservation of mechanical energy). For example, a falling object loses GPE and gains KE.
在许多情况下，能量在 GPE 和 KE 之间转换。如果忽略空气阻力，GPE 与 KE 之和保持不变（机械能守恒）。例如，下落的物体会失去 GPE 并增加 KE。
7. Power and Efficiency | 功率与效率
Power is the rate at which work is done or energy is transferred. A higher power means more energy is transferred per second. Power is measured in watts (W). One watt equals one joule per second.
功率是做功或能量转移的速率。功率越高，每秒转移的能量越多。功率的单位是瓦特（W）。1 瓦特等于每秒 1 焦耳。
power = work done ÷ time P = W / t
Since work done = energy transferred, you can also write P = E / t.
由于功等于能量转移，你也可以写成 P = E / t。
- P = power (W)
- W or E = work or energy (J)
- t = time (s)
Efficiency tells us how good a device is at transferring input energy into useful output energy. It can be expressed as a decimal or a percentage.
效率 表示设备将输入能量转换为有用输出能量的能力。可以用小数或百分比表示。
efficiency = useful output energy ÷ total input energy
efficiency (%) = (useful output energy / total input energy) × 100%
Efficiency has no unit because it is a ratio. No device can be 100% efficient because some energy is always dissipated as heat to the surroundings.
效率没有单位，因为它是一个比值。没有设备能达到 100% 的效率，因为总有一部分能量以热能形式散失到环境中。
8. Current, Voltage and Resistance | 电流、电压与电阻
Electric current is the rate of flow of charge. The unit of current is the ampere (A). In a circuit, current flows from the positive terminal to the negative terminal of a battery (conventional current). Voltage (potential difference) measures the energy transferred per unit of charge. Resistance measures how much a component opposes the flow of current.
电流是电荷流动的速率，单位是安培（A）。在电路中，电流从电池正极流向负极（传统电流方向）。电压（电势差）衡量每单位电荷转移的能量。电阻衡量元件对电流阻碍作用的大小。
charge = current × time Q = I t
- Q = charge (coulombs, C)
- I = current (A)
- t = time (s)
voltage = current × resistance V = I R
- V = voltage (volts, V)
- I = current (A)
- R = resistance (ohms, Ω)
Ohm's Law states that, at constant temperature, the current through a conductor is directly proportional to the voltage across it. The resistance of a wire depends on its material, length, and cross-sectional area.
欧姆定律指出，在温度恒定下，通过导体的电流与导体两端的电压成正比。导线的电阻取决于材料、长度和横截面积。
9. Series and Parallel Circuits | 串联与并联电路
In a series circuit, components are connected end to end. The current is the same through all components. The total voltage supplied by the battery is shared across the components, and the total resistance is the sum of individual resistances.
在串联电路中，元件首尾相连。电流处处相等。电池提供的总电压由各元件分担，总电阻等于各个电阻之和。
- I (total) = I₁ = I₂
- V (total) = V₁ + V₂
- R (total) = R₁ + R₂ + ...
In a parallel circuit, components are connected on separate branches. The voltage across each branch is equal to the supply voltage. The total current is the sum of the currents in the branches. The total resistance is less than the smallest individual resistance.
在并联电路中，元件连接在不同的支路上。各支路两端的电压相等，等于电源电压。总电流等于各支路电流之和。总电阻小于最小的单个电阻。
- V (total) = V₁ = V₂
- I (total) = I₁ + I₂
- 1 / R (total) = 1/R₁ + 1/R₂
Adding more resistors in series increases total resistance. Adding more resistors in parallel decreases total resistance.
串联增加电阻会使总电阻增大。并联增加电阻会使总电阻减小。
10. Waves: Speed, Frequency and Wavelength | 波：波速、频率与波长
Waves transfer energy without transferring matter. Transverse waves (e.g. light, water waves) have oscillations perpendicular to the direction of energy transfer. Longitudinal waves (e.g. sound) have oscillations parallel to the direction of energy transfer.
波传递能量而不传递物质。横波（如光波、水波）的振动方向与能量传递方向垂直。纵波（如声波）的振动方向与能量传递方向平行。
wave speed = frequency × wavelength v = f λ
- v = wave speed (m/s)
- f = frequency (hertz, Hz)
- λ (lambda) = wavelength (m)
Frequency is the number of complete waves passing a point per second. The period (T) is the time for one complete wave, and f = 1 / T.
频率是每秒通过某点的完整波的数量。周期（T）是一个完整波所需的时间，并且 f = 1 / T。
vacuum: c ≈ 3.0 × 10⁸ m/s. This constant can be used with the wave equation for EM waves: c = f λ.
所有电磁波在真空中的传播速度相同：c ≈ 3.0 × 10⁸ m/s。这个常数可以代入波速方程用于电磁波：c = f λ。
When waves change medium, speed and wavelength may change, but frequency remains constant. This explains refraction.
当波改变介质时，波速和波长可能改变，但频率保持不变。这可以解释折射现象。
11. Pressure in Fluids | 流体中的压强
Pressure is the force applied per unit area. It is a scalar quantity measured in pascals (Pa). One pascal is equivalent to one newton per square metre.
压强是单位面积上施加的力，是标量，单位为帕斯卡（Pa）。1 帕斯卡等于每平方米 1 牛顿。
pressure = force ÷ area p = F / A
- p = pressure (Pa)
- F = force (N)
- A = area (m²)
For a given force, a smaller area gives a larger pressure. This is why sharp objects cut more easily.
当力一定时，面积越小压强越大。这就是尖锐物体更容易切割的原因。
In a liquid, pressure increases with depth and with the density of the liquid. The formula for pressure at a depth h in a liquid of density ρ is:
在液体中，压强随深度和液体密度的增大而增大。密度为 ρ 的液体在深度 h 处的压强公式为：
p = ρ g h
- ρ = density (kg/m³)
- g = gravitational field strength (N/kg)
- h = depth (m)
Pressure in a liquid acts equally in all directions at a given depth.
在液体中某一深度，压强向各个方向大小相等。
12. Density and States of Matter | 密度与物质状态
Density is the mass per unit volume of a substance. It tells us how tightly matter is packed. Solids and liquids are often much denser than gases. Density is a property of materials, not of objects.
密度是单位体积的质量，表示物质排列的紧密程度。固体和液体通常比气体密度大得多。密度是材料的属性，而不是物体的属性。
density = mass ÷ volume ρ = m / V
- ρ (rho) = density (kg/m³ or g/cm³)
- m = mass (kg or g)
- V = volume (m³ or cm³)
To measure the density of a regular solid, find its mass using a balance, calculate its volume from length measurements, then apply the formula. For an irregular solid, use a displacement method (e.g. Eureka can) to find volume.
测量规则固体的密度时，用天平测质量，根据长度测量计算体积，然后代入公式。对于不规则固体，用排水法（如溢水罐）测量体积。
For a liquid, measure the mass of an empty measuring cylinder, add the liquid, measure the new mass, and read the volume directly from the cylinder.
测量液体密度时，先测量空量筒的质量，加入液体后再测总质量，体积直接从量筒读取。
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