📚 Year 8 WJEC Physics Formula & Theorem Quick Reference Handbook | Year 8 WJEC 物理：公式定理速查手册
This quick reference handbook compiles the essential formulas and theorems you need for Year 8 WJEC Physics. Each concept is paired with clear explanations, units, and example rearrangements to help you solve problems confidently. Whether you are revising forces, energy, electricity, or waves, this resource will keep the key relationships at your fingertips.
这本速查手册整理了Year 8 WJEC物理所需的关键公式和定理。每个概念都配有清晰的解释、单位和公式变形示例，帮助你自信地解决问题。不论你是在复习力、能量、电学还是波动，这份资料都能让你随时查阅核心关系式。
1. Speed, Distance and Time | 速度、距离和时间
Speed tells you how fast an object is moving. It is a scalar quantity, meaning it only has magnitude and no direction.
速度表示物体运动的快慢。它是一个标量，只有大小没有方向。
Average Speed (m/s) = Distance travelled (m) ÷ Time taken (s)
平均速度（m/s）= 行驶距离（m）÷ 所用时间（s）
earrange the formula: Distance = Speed × Time. To find time, use: Time = Distance ÷ Speed.
求距离时，可将公式变形为：距离 = 速度 × 时间。求时间时则用：时间 = 距离 ÷ 速度。
Always check that your units match. If distance is in kilometres and time in hours, speed will be in km/h. Convert to metres per second by dividing km/h by 3.6.
务必确保单位统一。若距离是千米、时间是小时，速度单位就是 km/h。将 km/h 除以 3.6 即可换算成 m/s。
2. Acceleration | 加速度
Acceleration measures how quickly the velocity of an object changes. It is a vector quantity, meaning it has both magnitude and direction.
加速度衡量物体速度变化的快慢。它是矢量，既有大小也有方向。
Acceleration (m/s²) = Change in velocity (m/s) ÷ Time taken (s)
加速度（m/s²）= 速度变化量（m/s）÷ 所用时间（s）
here v is the final velocity and u is the initial velocity. If the acceleration is negative, the object is decelerating.
这个公式常写作 a = (v - u) / t，其中 v 是末速度，u 是初速度。若加速度为负值，表示物体在减速。
On a speed–time graph, acceleration is the gradient of the line. A straight sloping line represents constant acceleration.
在速度–时间图上，加速度对应图线的斜率。一条倾斜的直线表示匀加速度。
3. Density | 密度
Density describes how much mass is packed into a given volume. It helps identify materials and predict whether objects will float or sink.
密度描述单位体积内所含质量的多少。它可以用来鉴别材料，并判断物体是会漂浮还是下沉。
Density (kg/m³) = Mass (kg) ÷ Volume (m³)
密度（kg/m³）= 质量（kg）÷ 体积（m³）
You may also see density in g/cm³. Remember 1 g/cm³ equals 1000 kg/m³. To measure an irregular solid's volume, use a displacement can and measuring cylinder.
密度也可能以 g/cm³ 为单位。记住 1 g/cm³ 等于 1000 kg/m³。测量不规则固体的体积时，可使用溢水罐和量筒。
| Substance | Density (kg/m³) | 物质 |
|---|---|---|
| Water | 1000 | 水 |
| Air | 1.3 | 空气 |
| Iron | 7900 | 铁 |
4. Mass, Weight and Gravity | 质量、重量与重力
Mass is the amount of matter in an object and is measured in kilograms (kg). It stays the same everywhere in the universe.
质量是物体所含物质的多少，单位是千克（kg）。它在宇宙中任何地方都保持不变。
Weight is the force of gravity pulling on an object. It depends on the gravitational field strength (g) and is measured in newtons (N).
重量是重力作用在物体上的力。它取决于重力场强度（g），单位是牛顿（N）。
Weight (N) = Mass (kg) × Gravitational field strength (N/kg)
重量（N）= 质量（kg）× 重力场强度（N/kg）
.8 N/kg). On the Moon, g is only about 1.6 N/kg, so objects weigh much less but their mass does not change.
在地球上，g ≈ 10 N/kg（更精确为 9.8 N/kg）。在月球上，g 仅约 1.6 N/kg，所以物体的重量小得多，但质量不变。
5. Pressure | 压强
Pressure is a measure of how concentrated a force is over a given area. A large force on a small area produces high pressure.
压强衡量力在给定面积上的集中程度。大力作用在小面积上会产生高压强。
Pressure (Pa or N/m²) = Force (N) ÷ Area (m²)
压强（Pa 或 N/m²）= 力（N）÷ 面积（m²）
The unit pascal (Pa) is equal to one newton per square metre. To increase pressure, you can either increase the force or decrease the area – for example, a sharp knife has a very small area at the edge.
帕斯卡（Pa）这个单位等于每平方米一牛顿。增大压强可以通过增大作用力或减小面积来实现——例如，锋利的刀刃接触面积极小。
at a point in a liquid can be found using P = h ρ g, but this is explored in later years.
在液体和气体中，压强向各个方向传递，并随深度增加而增大。液体中某点的压强可用 P = h ρ g 计算，但这一内容在更高年级学习。
6. Moments | 力矩
A moment is the turning effect of a force about a pivot. It depends on the size of the force and the perpendicular distance from the pivot.
力矩是力对支点的转动效应，它取决于力的大小以及从支点到力的作用线的垂直距离。
Moment (N m) = Force (N) × Perpendicular distance from pivot (m)
力矩（N m）= 力（N）× 支点到力作用线的垂直距离（m）
The principle of moments states that for an object in rotational equilibrium, the total clockwise moment equals the total anticlockwise moment.
力矩原理指出，对于处于转动平衡的物体，顺时针方向的总力矩等于逆时针方向的总力矩。
This allows you to calculate unknown forces or distances in lever systems, seesaws, and beam balances. Always measure the perpendicular distance from the pivot to the line of action of the force.
利用这一原理，可以计算杠杆、跷跷板和横梁平衡中的未知力或距离。记住总是测量从支点到力作用线的垂直距离。
7. Work Done | 做功
Work is done when a force causes an object to move in the direction of the force. Energy is transferred whenever work is done.
当一个力使物体沿力的方向移动时，力就对物体做了功。做功一定伴随着能量的转移。
Work done (J) = Force (N) × Distance moved in direction of force (m)
做功（J）= 力（N）× 沿力方向移动的距离（m）
One joule of work is done when a force of one newton moves an object one metre. If the object does not move, no work is done even if you feel tired holding it up.
当 1 N 的力使物体移动 1 m，所做的功就是 1 焦耳。如果物体没有移动，即使你举着它感到累，物理上也不做功。
Work done against friction is transferred to thermal energy, heating up the surfaces. Work done against gravity increases the object's gravitational potential energy.
克服摩擦力做功会转化为内能，使接触面温度升高。克服重力做功则会增加物体的重力势能。
8. Kinetic Energy and Gravitational Potential Energy | 动能与重力势能
Kinetic energy (KE) is the energy possessed by a moving object. Gravitational potential energy (GPE) is the energy stored due to an object's height above the ground.
动能是运动物体所具有的能量。重力势能是由于物体被举高而储存的能量。
KE (J) = ½ × Mass (kg) × (Velocity)²
动能（J）= ½ × 质量（kg）×（速度）²
GPE (J) = Mass (kg) × g (N/kg) × Height (m)
重力势能（J）= 质量（kg）× g（N/kg）× 高度（m）
In many situations, energy converts between KE and GPE. For a falling object with no air resistance, the loss of GPE equals the gain in KE.
在许多情况下，能量在动能和重力势能之间相互转换。对于不受空气阻力影响的落体，重力势能的减少量等于动能的增加量。
Using these formulas together with the principle of conservation of energy lets you predict speeds just before impact.
结合使用这两个公式和能量守恒原理，可以计算出物体撞击地面前的速度。
9. Power | 功率
Power is the rate at which work is done or energy is transferred. A more powerful machine does the same amount of work in less time.
功率是做功或能量转换的快慢程度。功率越大的机器，做同样的功所需时间越短。
Power (W) = Work done (J) ÷ Time (s)
功率（W）= 做功（J）÷ 时间（s）
You might also calculate power from energy transferred: Power = Energy transferred ÷ Time.
一瓦特相当于每秒一焦耳。你也可以用能量转移量来求功率：功率 = 转移的能量 ÷ 时间。
If you know the object' n find power output for a vehicle moving at constant velocity using Power = Force × Speed.
若已知物体的速度和阻力大小，还可以用 Power = Force × Speed 计算匀速行驶的车辆的功率输出。
10. Ohm's Law | 欧姆定律
Ohm's law links voltage, current, and resistance in a circuit. It applies to ohmic conductors at constant temperature.
欧姆定律描述了电路中电压、电流和电阻之间的关系。它适用于温度恒定条件下的欧姆导体。
Voltage (V) = Current (A) × Resistance (Ω)
电压（V）= 电流（A）× 电阻（Ω）
written as V = I R. To find current, rearrange: I = V ÷ R. To find resistance: R = V ÷ I.
该定律常写作 V = I R。求电流时可变形为 I = V ÷ R。求电阻时则用 R = V ÷ I。
In a series circuit, current is the same everywhere, and the total resistance is the sum of individual resistances. In a parallel circuit, voltage is the same across each branch.
在串联电路中，电流处处相等，总电阻为各电阻之和。在并联电路中，各支路两端的电压相等。
11. Wave Speed | 波速
Waves transfer energy without transferring matter. The speed of a wave depends on its frequency and wavelength.
波在传递能量时不传递物质。波速取决于波的频率和波长。
Wave speed (m/s) = Frequency (Hz) × Wavelength (m)
波速（m/s）= 频率（Hz）× 波长（m）
uency is the number of complete waves passing a point per second, and wavelength is the distance between two corresponding points on adjacent waves.
这个公式常写作 v = f λ。频率是每秒通过某点的完整波数，波长是相邻波上对应点之间的距离。
When a wave enters a different medium, its speed and wavelength may change, but its frequency stays the same. This explains refraction.
当波进入另一种介质，其速度和波长可能改变，但频率保持不变。这解释了折射现象。
12. Efficiency of Energy Transfers | 能量转换效率
Whenever energy is transferred, some is often wasted, typically as thermal energy. Efficiency tells us the proportion of input energy that is converted to useful output.
能量在传递过程中总有一部分被浪费掉，常常表现为内能。效率表示输入能量中被转化为有用输出能量的比例。
Efficiency = (Useful output energy ÷ Total input energy) × 100%
效率 =（有用的输出能量 ÷ 总输入能量）× 100%
culate efficiency from power: Efficiency = (Useful power output ÷ Total power input) × 100%. No device can be more than 100% efficient.
你也可以用功率来计算效率：效率 =（有用的输出功率 ÷ 总输入功率）× 100%。任何装置的效率都不可能超过 100%。
Reducing unwanted energy transfers, such as lubricating moving parts or adding insulation, improves efficiency and saves energy.
减少不必要的能量损耗，比如给运动部件加润滑油或增加隔热层，可以提高效率并节省能源。
Published by TutorHao | Physics Revision Series | aleveler.com
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