📚 Year 7 WJEC Science: Formulas and Theorems Quick Reference Handbook | 七年级 WJEC 科学：公式定理速查手册
This handbook brings together all the essential formulas, equations and key principles you will meet in Year 7 WJEC Science. Use it to check units, practise rearranging equations and build confidence in calculations for physics, chemistry and biology.
本手册汇集了七年级 WJEC 科学课程中所有重要的公式、方程和关键原理。你可以用它核实单位、练习变形公式，并在物理、化学和生物的计算中建立信心。
1. Speed, Distance and Time | 速度、路程与时间
To find the average speed of an object that travels in a straight line, divide the total distance travelled by the time taken.
要计算直线运动的物体的平均速度，用经过的总路程除以所花费的时间。
speed = distance ÷ time
tten in symbols as v = d / t, where v is speed (m/s), d is distance (m) and t is time (s).
文字方程可用符号表示为 v = d / t，其中 v 是速度 (m/s)，d 是路程 (m)，t 是时间 (s)。
| Symbol | Quantity | SI Unit |
|---|---|---|
| v | speed | metres per second (m/s) |
| d | distance travelled | metres (m) |
| t | time taken | seconds (s) |
the quantities, you can rearrange the equation to find the third: d = v × t or t = d / v.
如果你知道其中任意两个量，就可以变形公式求出第三个量：d = v × t 或 t = d / v。
2. Density | 密度
Density describes how much mass is packed into a given volume. Materials with closely packed particles have a higher density.
密度描述的是单位体积内所含的质量。粒子排列越紧密的材料密度越大。
density = mass ÷ volume
is density (kg/m³), m is mass (kg) and V is volume (m³). For smaller samples units of g/cm³ are often used.
符号方程为 ρ = m / V，其中 ρ 为密度 (kg/m³)，m 为质量 (kg)，V 为体积 (m³)。测量较小的样品常用 g/cm³ 为单位。
of wood has a mass of 400 g and a volume of 500 cm³. Its density is 400 ÷ 500 = 0.8 g/cm³.
例题：一块木头的质量为 400 g，体积为 500 cm³。它的密度是 400 ÷ 500 = 0.8 g/cm³。
3. Force, Mass and Weight | 力、质量与重量
Weight is the force of gravity acting on an object. It is not the same as mass – mass is the amount of matter and does not change with location.
重量是作用在物体上的引力。它不同于质量——质量是物体所含物质的多少，不随位置变化。
weight = mass × gravitational field strength
g is gravitational field strength (N/kg). On Earth g ≈ 9.8 N/kg, often rounded to 10 N/kg.
用符号表示：W = m × g，W 为重量 (N)，m 为质量 (kg)，g 为引力场强度 (N/kg)。地球表面的 g 约等于 9.8 N/kg，通常可近似取 10 N/kg。
For instance, an object weighing 50 N on Earth has a mass of about 5 kg (50 N ÷ 10 N/kg).
变形求质量：m = W / g。例如，地面上一个重 50 N 的物体，其质量约为 5 kg (50 N ÷ 10 N/kg)。
4. Pressure | 压强
Pressure measures how concentrated a force is over an area. A sharp knife exerts a higher pressure than a blunt one because the same force acts over a smaller area.
压强表示力作用在面积上的集中程度。锋利的刀比钝刀产生的压强大，因为相同的力作用在更小的面积上。
pressure = force ÷ area
P in pascals (Pa), force F in newtons (N) and area A in square metres (m²). 1 Pa = 1 N/m².
符号方程：P = F / A，压强 P 的单位是帕斯卡 (Pa)，力 F 的单位是牛顿 (N)，面积 A 的单位是平方米 (m²)。1 Pa = 1 N/m²。
| Variable | Meaning | Unit |
|---|---|---|
| P | pressure | pascal (Pa) |
| F | force | newton (N) |
| A | area | square metre (m²) |
Liquids and gases also exert pressure. In a liquid, pressure increases with depth due to the weight of the water above.
液体和气体也会产生压强。在液体中，由于上方水的重量，压强随深度增加而增大。
5. Work Done, Energy Transferred and Power | 做功、能量传递与功率
When a force moves an object through a distance, work is done. Energy is transferred mechanically from one store to another.
当一个力使物体在力的方向上移动一段距离时，就做了功。能量通过机械方式从一个储存体传递到另一个。
work done = force × distance moved (in the direction of the force)
e (J), F is force (N) and d is distance moved in metres (m). Work and energy are both measured in joules.
用符号表示：W = F × d，W 为做功 (J)，F 为力 (N)，d 为在力的方向上移动的距离 (m)。功和能量的单位都是焦耳。
taken, or P = E / t, where P is power (W), E is energy transferred (J) and t is time (s).
功率是能量传递或做功的速率。功率 = 做的功 ÷ 所用时间，或 P = E / t，P 为功率 (W)，E 为传递的能量 (J)，t 为时间 (s)。
lamp transfers 600 J of electrical energy in 30 seconds. Its power is 600 J ÷ 30 s = 20 W.
例题：一盏灯在 30 秒内传递了 600 J 的电能。它的功率为 600 J ÷ 30 s = 20 W。
6. Gravitational Potential Energy | 重力势能
An object lifted upwards gains gravitational potential energy (GPE). The increase in GPE depends on its mass, the height gained and the strength of gravity.
物体被抬高时会获得重力势能 (GPE)。重力势能的增加量取决于物体的质量、升高的高度以及重力场强度。
change in GPE = mass × gravitational field strength × change in height
is gravitational potential energy (J), m is mass (kg), g is gravitational field strength (N/kg) and h is height (m).
符号方程：Eₚ = m × g × h，Eₚ 为重力势能 (J)，m 为质量 (kg)，g 为引力场强度 (N/kg)，h 为高度 (m)。
ook is lifted 1.5 m onto a shelf, and g = 10 N/kg, the gain in GPE is 2 × 10 × 1.5 = 30 J.
如果把一本 2 kg 的书抬高 1.5 m 放到书架上，g 取 10 N/kg，增加的重力势能为 2 × 10 × 1.5 = 30 J。
7. Ohm's Law: Voltage, Current and Resistance | 欧姆定律：电压、电流与电阻
In an electrical circuit, the current flowing through a resistor is directly proportional to the potential difference (voltage) across it, provided the temperature remains constant.
在电路中，只要温度保持恒定，通过电阻器的电流就与它两端的电势差（电压）成正比。
potential difference = current × resistance
V = I × R, where V is potential difference (V), I is current (A) and R is resistance (Ω).
符号方程：V = I × R，V 为电压 (V)，I 为电流 (A)，R 为电阻 (Ω)。
| Symbol | Quantity | Unit |
|---|---|---|
| V | potential difference (voltage) | volt (V) |
| I | current | ampere (A) |
| R | resistance | ohm (Ω) |
resistance of 4 Ω connected to a 6 V battery draws a current of I = V / R = 6 / 4 = 1.5 A.
一个电阻为 4 Ω 的元件连接在 6 V 的电池上时，通过的电流为 I = V / R = 6 / 4 = 1.5 A。
8. Wave Speed, Frequency and Wavelength | 波速、频率与波长
Waves transfer energy without transferring matter. The speed of a wave depends on its frequency and its wavelength.
波传递能量而不传递物质。波速取决于波的频率和波长。
wave speed = frequency × wavelength
f × λ, where v is wave speed (m/s), f is frequency (Hz) and λ (lambda) is wavelength (m).
符号方程：v = f × λ，v 为波速 (m/s)，f 为频率 (Hz)，λ (lambda) 为波长 (m)。
s a frequency of 500 Hz and a wavelength of 0.68 m, its speed is v = 500 × 0.68 = 340 m/s.
如果空气中的声波频率为 500 Hz，波长为 0.68 m，则波速为 v = 500 × 0.68 = 340 m/s。
You can also arrange the equation to find frequency: f = v / λ, or wavelength: λ = v / f.
你也可以将公式变形以求出频率：f = v / λ，或求波长：λ = v / f。
9. Magnification (Biology) | 放大倍率（生物）
When using a microscope, you can calculate how many times larger the image appears compared with the actual size of the specimen.
使用显微镜时，你可以计算出图像比标本实际尺寸放大了多少倍。
magnification = image size ÷ actual size
written as ×10, ×40), I is image size and A is actual size. Both must be in the same unit.
用符号表示：M = I / A，M 为放大倍率（无单位，常写作 ×10、×40），I 为图像尺寸，A 为实际尺寸。两者必须使用相同的单位。
Example: A cell image measures 8 cm across, but the cell's actual diameter is 0.02 cm. Magnification = 8 ÷ 0.02 = 400×.
例题：一个细胞的图像宽度为 8 cm，而细胞实际直径为 0.02 cm。放大倍率 = 8 ÷ 0.02 = 400×。
10. Reaction Rate (Chemistry) | 反应速率（化学）
The rate of a chemical reaction tells us how quickly a reactant is used up or a product is formed. It can be found by measuring changes over time.
化学反应速率表示反应物被消耗或生成物产生的快慢。可以通过测量随时间的变化而求出。
mean rate of reaction = quantity of reactant used or product formed ÷ time
The quantity can be measured as mass (g) for solids, volume (cm³) for gases, or change in concentration (g/cm³). Time is normally measured in seconds (s).
反应物的使用量或生成物的量可以用固体质量 (g)、气体体积 (cm³) 或浓度变化 (g/cm³) 来衡量。时间通常以秒 (s) 为单位。
if 30 cm³ of hydrogen gas is produced in 15 seconds, the mean rate = 30 ÷ 15 = 2.0 cm³/s.
例如，如果 15 秒内生成了 30 cm³ 的氢气，则平均速率 = 30 ÷ 15 = 2.0 cm³/s。
11. Conservation of Mass | 质量守恒
In a chemical reaction, the total mass of the products is always equal to the total mass of the reactants. This is the law of conservation of mass.
在化学反应中，生成物的总质量总是等于反应物的总质量。这就是质量守恒定律。
id, the total mass of products formed will be 5.3 + 3.6 = 8.9 g, provided nothing escapes.
如果 5.3 g 碳酸钠与 3.6 g 盐酸反应，只要没有物质逸出，生成物的总质量就是 5.3 + 3.6 = 8.9 g。
In an open container, gas may escape and the measured mass can decrease, but the atoms have not been destroyed – they have just moved away.
在敞口容器中，气体可能会逸出，测得的质量会减小，但这并不代表原子被消灭了——它们只是散逸到空气中了。
12. Energy Efficiency and Energy Conservation | 能量效率与能量守恒
Energy cannot be created or destroyed, only transferred from one store to another or dissipated (spread out) to the surroundings. This is the principle of conservation of energy.
能量既不会凭空产生，也不会凭空消失，它只能从一个储存体转移到另一个，或耗散（扩散）到周围环境中。这就是能量守恒原理。
Efficiency tells us how much of the energy supplied to a device is transferred usefully. Unwanted energy is often dissipated as heat.
效率表示供给设备的能量中有多少被有效地传递。无用的能量通常以热的形式耗散。
efficiency = useful output energy transfer ÷ total input energy transfer
Efficiency can be written as a decimal between 0 and 1, or as a percentage by multiplying by 100.
效率可以用 0 到 1 之间的小数表示，也可以乘以 100 转化为百分数。
GPE energy while drawing 100 J of electrical energy. Efficiency = 80 J ÷ 100 J = 0.8 or 80%.
例题：一台电动机将重物提起，有效地传递了 80 J 的动能和重力势能，而消耗了 100 J 的电能。效率 = 80 J ÷ 100 J = 0.8 或 80%。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图