📚 Year 7 Cambridge Science Formula and Theorem Quick Reference Handbook | Year 7 剑桥科学公式定理速查手册
This quick reference handbook brings together all the essential formulas and theorems you will meet in Year 7 Cambridge Science. From calculating speed and density to understanding the laws that govern energy, electricity and living things, each key idea is presented with a clear equation or statement, worked examples and careful explanations. Use this guide to review for tests, complete homework with confidence and build strong foundations for future study.
这本速查手册汇集了 Year 7 剑桥科学课程中你将会遇到的所有核心公式与定理。从计算速度和密度，到理解支配能量、电学与生物的那些定律，每一个关键概念都以清晰的方程式或陈述呈现，并配有例题和详细解释。你可以用它来复习测验、自信地完成作业，并为未来的学习打下扎实的基础。
1. Speed and Motion | 速度与运动
The speed of a moving object tells us how far it travels in a certain amount of time. To calculate average speed, you divide the total distance moved by the time taken. This relationship is one of the most useful equations in physics.
运动物体的速度告诉我们它在一定时间内移动了多远。要计算平均速度，你可以用移动的总距离除以所用的时间。这个关系是物理学中最有用的方程之一。
speed = distance ÷ time
速度 = 距离 ÷ 时间
| Symbol | Quantity | SI unit | Other common units |
|---|---|---|---|
| v or s | speed | metres per second (m/s) | km/h, mph |
| d | distance | metre (m) | km, cm |
| t | time | second (s) | minute, hour |
| 符号 | 物理量 | 国际单位 | 其他常用单位 |
|---|---|---|---|
| v 或 s | 速度 | 米每秒 (m/s) | 千米/时，英里/时 |
| d | 距离 | 米 (m) | 千米，厘米 |
| t | 时间 | 秒 (s) | 分钟，小时 |
If a cyclist travels 150 metres in 30 seconds, her speed is 150 ÷ 30 = 5 m/s. The same formula can be rearranged: distance = speed × time and time = distance ÷ speed.
如果一位自行车手在 30 秒内骑行了 150 米，她的速度就是 150 ÷ 30 = 5 m/s。同一个公式可以变形：距离 = 速度 × 时间，时间 = 距离 ÷ 速度。
2. Density | 密度
Density measures how much mass is packed into a given volume. Dense materials feel heavy for their size. The density of a substance is found by dividing its mass by its volume.
密度衡量一定体积内包含有多少质量。密度大的材料相对于其大小会显得更重。一种物质的密度可以通过将其质量除以体积求得。
density = mass ÷ volume
密度 = 质量 ÷ 体积
| Symbol | Quantity | SI unit | Other units |
|---|---|---|---|
| ρ (rho) or D | density | kilograms per cubic metre (kg/m³) | g/cm³ |
| m | mass | kilogram (kg) | g |
| V | volume | cubic metre (m³) | cm³, mL |
| 符号 | 物理量 | 国际单位 | 其他单位 |
|---|---|---|---|
| ρ (rho) 或 D | 密度 | 千克每立方米 (kg/m³) | 克每立方厘米 (g/cm³) |
| m | 质量 | 千克 (kg) | 克 (g) |
| V | 体积 | 立方米 (m³) | 立方厘米 (cm³)，毫升 (mL) |
A block of metal with a mass of 200 g and a volume of 40 cm³ has a density of 200 ÷ 40 = 5 g/cm³. Objects with a density less than that of water (1 g/cm³) will float; those with a greater density sink.
一块质量为 200 g、体积为 40 cm³ 的金属，密度为 200 ÷ 40 = 5 g/cm³。密度小于水（1 g/cm³）的物体会浮起；密度更大的物体则会下沉。
3. Pressure | 压力
Pressure tells us how concentrated a force is over an area. The same force creates high pressure when spread over a small area, and low pressure when spread over a large area. The formula relates force and area.
压力告诉我们力在某一面积上的集中程度。相同大小的力作用在较小的面积上会产生较大的压强，而作用在较大的面积上则压强较小。这个公式将力与面积联系起来。
pressure = force ÷ area
压强 = 力 ÷ 面积
| Symbol | Quantity | Unit |
|---|---|---|
| P | pressure | pascal (Pa) or N/m² |
| F | force | newton (N) |
| A | area | square metre (m²) |
| 符号 | 物理量 | 单位 |
|---|---|---|
| P | 压强 | 帕斯卡 (Pa) 或 N/m² |
| F | 力 | 牛顿 (N) |
| A | 面积 | 平方米 (m²) |
A person weighing 600 N standing on a board with an area of 2 m² exerts a pressure of 600 ÷ 2 = 300 Pa. Snowshoes work by increasing area to reduce pressure, preventing you from sinking into the snow.
一个体重 600 N 的人站在面积为 2 m² 的板上，产生的压强为 600 ÷ 2 = 300 Pa。雪地靴通过增大面积来减小压强，防止你陷入雪中。
4. Weight and Mass | 重量与质量
Weight is the force of gravity pulling on a mass. Mass is the amount of matter in an object and does not change with location, whereas weight depends on the gravitational field strength. On Earth the gravitational field strength is approximately 10 N/kg.
重量是作用在质量上的重力。质量是物体所含物质的多少，不会因位置而改变；而重量则取决于引力场强度。在地球表面，引力场强度约为 10 N/kg。
weight = mass × gravitational field strength
W = m × g
On Earth: g ≈ 10 N/kg
重量 = 质量 × 引力场强度
W = m × g
在地球上：g ≈ 10 N/kg
| Symbol | Quantity | Unit |
|---|---|---|
| W | weight | newton (N) |
| m | mass | kilogram (kg) |
| g | gravitational field strength | newtons per kilogram (N/kg) |
| 符号 | 物理量 | 单位 |
|---|---|---|
| W | 重量 | 牛顿 (N) |
| m | 质量 | 千克 (kg) |
| g | 引力场强度 | 牛顿每千克 (N/kg) |
A 5 kg medicine ball on Earth has a weight W = 5 × 10 = 50 N. On the Moon, where g ≈ 1.6 N/kg, the same ball would weigh only 8 N, although its mass is still 5 kg.
地球上一个 5 kg 的药球，重量 W = 5 × 10 = 50 N。在月球上，g ≈ 1.6 N/kg，同一个球的重量只有 8 N，但其质量依然是 5 kg。
5. Moments | 力矩
A moment is the turning effect of a force. It depends on two things: the size of the force and the perpendicular distance from the pivot (the point about which the object turns). Moments explain how levers work and why a longer spanner makes it easier to undo a tight nut.
力矩是力的转动效应。它取决于两个因素：力的大小以及力到支点（物体绕其转动的点）的垂直距离。力矩解释了杠杆的原理，也说明了为什么较长的扳手更容易拧松紧固的螺母。
moment = force × perpendicular distance from pivot
M = F × d
力矩 = 力 × 支点到力作用线的垂直距离
M = F × d
| Symbol | Quantity | Unit |
|---|---|---|
| M | moment | newton metre (Nm) |
| F | force | newton (N) |
| d | perpendicular distance | metre (m) |
| 符号 | 物理量 | 单位 |
|---|---|---|
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