📚 Year 7 AQA Science: Formulas & Theorems Quick Reference | Year 7 AQA 科学：公式定理速查手册
This handbook gathers the essential formulas and principles you will meet in Year 7 AQA Science. Use it to quickly check a relationship, practise rearranging equations, or remind yourself of the key scientific laws behind the topics of forces, energy, electricity, chemistry and biology.
本手册汇集了你在 Year 7 AQA 科学中将遇到的核心公式和定理。你可以用它快速查阅某个关系、练习公式变形，或者重温力学、能量、电学、化学和生物学主题背后的关键科学定律。
1. Speed Formula | 速度公式
Speed describes how fast an object moves. It is calculated by dividing the distance travelled by the time taken.
速度描述物体运动的快慢。它等于物体通过的距离除以所用的时间。
speed = distance / time
The standard unit of speed is metres per second (m/s). Distance should be measured in metres (m) and time in seconds (s).
速度的标准单位是米每秒 (m/s)。距离应以米 (m) 为单位，时间以秒 (s) 为单位。
ormula to find the other quantities: distance = speed × time, and time = distance / speed.
你可以对公式进行变形来求其他量：距离 = 速度 × 时间，时间 = 距离 / 速度。
2. Density Formula | 密度公式
Density tells us how much mass is packed into a given volume. It is the mass per unit volume of a substance.
密度表示单位体积内所含物质的质量，即物质的质量与体积之比。
density = mass / volume
Mass is measured in kilograms (kg) or grams (g), and volume is measured in cubic metres (m³) or cubic centimetres (cm³). Density is often given in kg/m³ or g/cm³.
质量用千克 (kg) 或克 (g) 表示，体积用立方米 (m³) 或立方厘米 (cm³) 表示。密度的常用单位是 kg/m³ 或 g/cm³。
Materials with a density lower than water (1 g/cm³) will float; those with higher density will sink.
密度小于水 (1 g/cm³) 的物体会浮在水面；密度大于水的物体则会下沉。
3. Pressure Formula | 压强公式
Pressure measures how much force is applied over a certain area. It explains why sharp knives cut easily and wide tyres do not sink into mud.
压强衡量单位面积上所受的压力大小。它解释了为什么锋利的刀更容易切割，而宽轮胎不会陷入泥里。
pressure = force / area
Force is measured in newtons (N) and area in square metres (m²). The unit of pressure is the pascal (Pa), which is equal to one newton per square metre (N/m²).
力的单位是牛顿 (N)，面积单位是平方米 (m²)。压强的单位是帕斯卡 (Pa)，1 Pa 等于 1 N/m²。
To reduce pressure, increase the area over which the force acts; to increase pressure, concentrate the force on a smaller area.
要减小压强，可以增大受力面积；要增大压强，则把力集中在更小的面积上。
4. Weight and Mass | 重量与质量
Weight is the force of gravity acting on an object. It depends on the object's mass and the strength of the gravitational field.
重量是作用在物体上的重力。它取决于物体的质量以及重力场的强度。
weight = mass × gravitational field strength
W = m × g
On Earth, the gravitational field strength (g) is approximately 10 N/kg. Mass is measured in kilograms (kg), so weight comes out in newtons (N).
在地球上，重力场强度 (g) 约为 10 N/kg。质量以千克 (kg) 为单位，因此重量以牛顿 (N) 为单位。
Mass is the amount of matter in an object and does not change with location, whereas weight would be different on the Moon because g is smaller.
质量是物体所含物质的多少，不随位置改变；而重量在月球上会变小，因为月球上的 g 值更小。
5. Hooke's Law | 胡克定律
Hooke's Law describes how springs and elastic objects behave when forces are applied. The extension of a spring is directly proportional to the force stretching it, as long as the elastic limit is not exceeded.
胡克定律描述了弹簧和弹性物体在受力时的行为。在不超过弹性限度的情况下，弹簧的伸长量与作用在它上面的力成正比。
force = spring constant × extension
F = k × e
Force (F) is in newtons (N), extension (e) in metres (m), and the spring constant (k) in newtons per metre (N/m). The spring constant tells you how stiff the spring is.
力 (F) 的单位是牛顿 (N)，伸长量 (e) 的单位是米 (m)，弹簧常数 (k) 的单位是牛顿每米 (N/m)。弹簧常数表示弹簧的劲度。
If you plot force against extension on a graph, you will see a straight line through the origin until the elastic limit is reached.
将力与伸长量绘制成图，会看到一条过原点的直线，直到达到弹性极限为止。
6. Newton's First Law of Motion | 牛顿第一运动定律
Newton's First Law states that an object will remain at rest, or continue moving at a constant speed in a straight line, unless acted upon by an external resultant force.
牛顿第一定律指出，任何物体在不受外力作用时，总保持静止或匀速直线运动状态。
This is why a book stays still on a table until pushed, and why a rolling ball slows down — because friction and air resistance act as unbalanced forces.
这就解释了为什么桌上的书没人推就保持静止，以及为什么滚动的球会慢下来——因为摩擦力和空气阻力充当了不平衡的力。
Balanced forces mean no change in motion; unbalanced forces cause acceleration, deceleration or a change in direction.
平衡力意味着运动状态不改变；不平衡力则导致加速、减速或改变方向。
7. Ohm's Law | 欧姆定律
Ohm's Law links voltage, current and resistance in an electrical circuit. The current through a resistor is directly proportional to the voltage across it, provided the temperature remains constant.
欧姆定律把电路中的电压、电流和电阻联系了起来。在温度不变的情况下，通过一个电阻的电流与它两端的电压成正比。
voltage = current × resistance
V = I × R
Voltage (V) is measured in volts (V), current (I) in amperes (A), and resistance (R) in ohms (Ω). If you know two of these, you can calculate the third.
电压 (V) 的单位是伏特 (V)，电流 (I) 的单位是安培 (A)，电阻 (R) 的单位是欧姆 (Ω)。知道其中任意两个量，就可以求出第三个。
8. Work Done (Energy Transfer) | 做功（能量转移）
Work is done whenever a force moves an object. The amount of work done equals the energy transferred.
只要力使物体发生移动，就做了功。做功的大小等于转移的能量。
work done = force × distance
W = F × d
Work done (W) is measured in joules (J), force (F) in newtons (N), and distance (d) moved in the direction of the force in metres (m).
功 (W) 的单位是焦耳 (J)，力 (F) 的单位是牛顿 (N)，物体在力的方向上移动的距离 (d) 单位是米 (m)。
If you push a box with a force of 5 N and it slides 2 m across the floor, the work done is 10 J.
如果你用 5 N 的力推动一个箱子，使它在地面上滑行 2 m，那么做的功就是 10 J。
9. Conservation of Mass | 质量守恒定律
In a chemical reaction, the total mass of the reactants equals the total mass of the products. Atoms are rearranged, not created or destroyed.
在化学反应中，反应物的总质量等于生成物的总质量。原子只是重新排列，既没有凭空产生也没有凭空消失。
A simple example: when magnesium burns in oxygen, magnesium oxide is formed. If you measure the mass carefully in a closed system, the total mass remains unchanged.
一个简单的例子：镁在氧气中燃烧生成氧化镁。如果在一个封闭系统中仔细测量质量，总质量保持不变。
magnesium + oxygen → magnesium oxide
Open containers may appear to show a mass change because a gas escapes or enters; always think about whether the system is closed.
敞口容器可能表现出质量变化，因为有气体逸出或进入；一定要考虑系统是否封闭。
10. Photosynthesis Equation | 光合作用方程式
Plants make their own food using sunlight. Photosynthesis takes place in the chloroplasts and converts carbon dioxide and water into glucose and oxygen.
植物利用阳光制造自己的食物。光合作用在叶绿体中进行，将二氧化碳和水转化为葡萄糖和氧气。
The word equation for photosynthesis is:
光合作用的文字表达式为：
carbon dioxide + water → glucose + oxygen
The balanced chemical equation uses the symbols:
配平的化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Light energy is absorbed by chlorophyll, so photosynthesis only occurs when light is available.
叶绿素吸收光能，因此只有在有光的情况下光合作用才能进行。
11. Respiration Equation | 呼吸作用方程式
Aerobic respiration is the process that releases energy from glucose in the presence of oxygen. It occurs in the mitochondria of cells.
有氧呼吸是在氧气参与下从葡萄糖中释放能量的过程。它发生在细胞的线粒体中。
The word equation is:
文字表达式为：
glucose + oxygen → carbon dioxide + water (+ energy)
The balanced chemical equation is the reverse of photosynthesis:
配平的化学方程式正好是光合作用的逆反应：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
All living cells carry out respiration continuously to provide the energy needed for life processes such as growth, movement and repair.
所有活细胞都在持续进行呼吸作用，为生长、运动和修复等生命过程提供所需的能量。
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