KS3 WJEC Science: Formula and Theorem Quick Reference Handbook | KS3 WJEC 科学：公式定理速查手册

📚 KS3 WJEC Science: Formula and Theorem Quick Reference Handbook | KS3 WJEC 科学：公式定理速查手册

This quick reference handbook brings together all the essential formulas and theorems you need for KS3 WJEC Science. Each section presents a key relationship, explains the units, and gives a worked example so that you can apply the formula confidently in tests and practical work.

这本速查手册汇总了 KS3 WJEC 科学课程中你需要的所有关键公式和定理。每一部分展示一个重要的关系式，解释单位，并附上计算示例，帮助你在考试和实验操作中自信地运用这些公式。

1. Speed, Distance and Time | 速度、距离与时间公式

Speed is a measure of how fast an object moves. It is calculated using the formula:

速度衡量物体移动的快慢，用以下公式计算：

speed = distance ÷ time

where speed is in metres per second (m/s), distance in metres (m) and time in seconds (s).

其中速度单位是米每秒 (m/s)，距离单位是米 (m)，时间单位是秒 (s)。

The formula can be rearranged to find distance: distance = speed × time, or time: time = distance ÷ speed.

该公式可变换以计算距离：距离 = 速度 × 时间；或时间：时间 = 距离 ÷ 速度。

Example: A cyclist travels 300 m in 20 s. Speed = 300 ÷ 20 = 15 m/s.

示例：一名自行车手 20 秒行驶 300 米。速度 = 300 ÷ 20 = 15 m/s。

Speed units can also be kilometres per hour (km/h). To convert m/s to km/h multiply by 3.6. Average speed is the total distance divided by total time even if the speed changes during the journey.

速度单位也可以是千米每小时 (km/h)。将 m/s 转换为 km/h 需要乘以 3.6。平均速度是总距离除以总时间，即使途中速度发生变化也如此计算。

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2. Density, Mass and Volume | 密度、质量与体积公式

Density tells us how much mass is packed into a certain volume. The formula is:

密度表示单位体积内所含的质量，公式为：

density = mass ÷ volume

Often the symbol ρ (rho) is used: ρ = m ÷ V. Mass is in kilograms (kg) or grams (g), volume in cubic metres (m³) or cubic centimetres (cm³). Density is measured in kg/m³ or g/cm³.

常用符号 ρ 表示：ρ = m ÷ V。质量单位为千克 (kg) 或克 (g)，体积单位为立方米 (m³) 或立方厘米 (cm³)。密度单位为 kg/m³ 或 g/cm³。

Example: A block of mass 200 g has a volume of 50 cm³. Its density is 200 ÷ 50 = 4 g/cm³.

示例：一块质量为 200 g 的物体体积为 50 cm³，其密度为 200 ÷ 50 = 4 g/cm³。

Objects with density greater than water (1 g/cm³) sink, while those with lower density float. To find the volume of an irregular solid, you can submerge it in water and measure the displaced volume using a Eureka can.

密度大于水 (1 g/cm³) 的物体会下沉，密度小于水的物体则上浮。要测量不规则固体的体积，可将其浸入水中并用溢流杯测量排开的水的体积。

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3. Pressure, Force and Area | 压力、力与面积公式

Pressure measures the concentration of a force over an area. Use the equation:

压力衡量力作用在面积上的集中程度，公式为：

pressure = force ÷ area

where pressure is in pascals (Pa) or N/m², force in newtons (N), and area in square metres (m²).

其中压力单位是帕斯卡 (Pa) 或 N/m²，力单位是牛顿 (N)，面积单位是平方米 (m²)。

Larger area reduces pressure for the same force – this explains why snowshoes prevent sinking into snow. High-heeled shoes exert high pressure because the force is concentrated on a small area, whereas a tractor’s wide tyres spread the force to reduce pressure.

相同力下面积越大压力越小——这解释了为什么雪鞋可以防止陷入雪中。高跟鞋产生高压力因为力集中在小的面积上，而拖拉机宽轮胎将力分散以减小压力。

Example: A force of 100 N acts on an area of 0.5 m². Pressure = 100 ÷ 0.5 = 200 Pa.

示例：100 N 的力作用在 0.5 m² 的面积上。压力 = 100 ÷ 0.5 = 200 Pa。

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4. Work, Energy and Power | 功、能与功率公式

Work is done when a force moves an object, transferring energy. The equation is:

力使物体移动时就做了功，能量发生了转移。功的公式为：

work done = force × distance

Work (W) is measured in joules (J), force in newtons (N), and distance in metres (m). 1 J = 1 N m.

功 (W) 的单位是焦耳 (J)，力单位是牛顿 (N)，距离单位是米 (m)。1 J = 1 N m。

Power is the rate of doing work or transferring energy. The formulas are:

功率是做功或能量转移的速率，公式为：

power = work done ÷ time or power = energy transferred ÷ time

Power is measured in watts (W

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