📚 5.5.1 Pressure in Gases and the Particle Model | 5.5.1 气体压强与粒子模型
Gas pressure is a fundamental concept in physics that explains everything from inflating a balloon to breathing. In IGCSE Edexcel Science, understanding how particles in a gas create pressure, and how pressure changes with volume and temperature, is essential. This article explores the particle model, Boyle’s law, and real‑world applications of gas pressure.
气体压强是物理学中的一个基本概念，它解释了从给气球充气到人体呼吸的各种现象。在 IGCSE Edexcel 科学课程中，理解气体中的粒子如何产生压强，以及压强如何随体积和温度变化至关重要。本文将探讨粒子模型、玻意耳定律以及气体压强在实际生活中的应用。
1. What Is Pressure? | 什么是压强？
Pressure is defined as the force acting perpendicularly per unit area. It is measured in pascals (Pa), where 1 Pa = 1 N/m². A gas confined in a container exerts pressure on all inner surfaces because its particles collide with the walls.
压强定义为单位面积上垂直作用的力。压强的单位是帕斯卡（Pa），1 Pa = 1 N/m²。限制在容器内的气体会对所有内壁施加压强，因为其粒子与容器壁发生碰撞。
The formula for pressure is:
压强的公式为：
pressure = force ÷ area
An object like a sharp nail exerts high pressure with a small force because the area is tiny, while a wide tyre exerts lower pressure over a larger area.
像尖锐的钉子这样的物体，由于面积很小，只需很小的力就能产生很大的压强；而宽大的轮胎则在较大面积上产生较低的压强。
2. The Particle Model of Gases | 气体的粒子模型
All matter is made of tiny particles in constant random motion. In a gas, the particles are much further apart than in liquids or solids, move rapidly in all directions, and have negligible forces of attraction between them. This kinetic particle model explains why gases fill their containers and are easily compressed.
所有物质都是由不断进行随机运动的微小粒子组成的。在气体中，粒子之间的距离比液体或固体中远得多，朝各个方向快速运动，并且粒子之间的吸引力几乎可以忽略不计。这一动力学粒子模型解释了为什么气体会充满整个容器并且容易被压缩。
The key points of the gas particle model are:
气体粒子模型的要点如下：
- Particles move at high speeds in straight lines until they collide.
- Collisions with container walls and with each other are perfectly elastic (no kinetic energy is lost).
- The volume of the particles themselves is negligible compared to the total volume of the gas.
- There are no intermolecular forces between particles except during collisions.
- 粒子以高速沿直线运动，直至发生碰撞。
- 与容器壁和粒子之间的碰撞是完全弹性的（不损失动能）。
- 粒子本身的体积与气体的总体积相比可忽略不计。
- 除碰撞瞬间外，粒子间没有分子间作用力。
3. How Gas Particles Create Pressure | 气体粒子如何产生压强
Each time a gas particle strikes a container wall, it exerts a tiny force. Billions of such collisions every second produce a steady, average force over the wall’s area – this is the pressure we measure. The faster and more frequent the collisions, the greater the pressure.
每当一个气体粒子撞击容器壁时，都会施加一个微小的力。每秒数以十亿计的碰撞在壁面上产生了一个稳定的平均力——这就是我们所测得的压强。碰撞速度越快、越频繁，压强就越大。
If the gas is heated, particles gain kinetic energy, move faster, and hit the walls harder and more often. If the volume is reduced, particles have less space to move and collide with the walls more frequently. Both effects increase pressure.
如果气体受热，粒子获得动能，运动速度加快，碰撞壁面时力度更大、频率更高。如果体积减小，粒子活动的空间变小，与壁面碰撞的频率增加。这两种情况都会使压强升高。
4. Factors Affecting Gas Pressure | 影响气体压强的因素
Three main factors determine the pressure of a fixed amount of gas:
决定定量气体压强的三个主要因素是：
- The volume of the container – decreasing volume increases pressure (at constant temperature).
- The temperature – increasing temperature increases pressure (at constant volume).
- The number of particles (or mass of gas) – adding more gas increases pressure.
- 容器的体积——体积减小，压强增大（温度不变时）。
- 温度——温度升高，压强增大（体积不变时）。
- 粒子的数量（或气体的质量）——增加气体量会提高压强。
These relationships can be remembered by considering the particle collisions: more collisions per second or harder collisions mean higher pressure.
可以通过考虑粒子碰撞来记住这些关系：每秒碰撞次数越多或碰撞力度越大，压强就越高。
5. Boyle’s Law: The Pressure–Volume Relationship | 玻意耳定律：压强与体积的关系
Boyle’s law states that for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume. In other words, if the volume doubles, the pressure halves, and vice versa.
玻意耳定律指出，对于一定质量的气体，在温度保持不变时，压强与体积成反比。换句话说，如果体积变为原来的两倍，压强就减半，反之亦然。
The law can be written as:
该定律可写作：
pV = constant
This constant depends on the mass of gas and its temperature. When the temperature is held steady, any change in volume is matched by an opposite change in pressure so that the product pV remains the same.
这个常数取决于气体的质量和温度。当温度保持不变时，体积的任何变化都会被压强的相反变化所平衡，从而使乘积 pV 保持恒定。
6. Mathematical Expression of Boyle’s Law | 玻意耳定律的数学表达式
For two states (initial and final) of the same fixed mass of gas at constant temperature:
对于同一固定质量的气体，在恒温下的两个状态（初始与最终），有：
p₁V₁ = p₂V₂
Where p₁ and V₁ are the initial pressure and volume, and p₂ and V₂ are the final pressure and volume. The units for pressure should be consistent (e.g. Pa, kPa, atm) and for volume (e.g. m³, cm³, dm³).
其中 p₁ 和 V₁ 是初始的压强与体积，p₂ 和 V₂ 是最终的压强与体积。压强和体积的单位应保持一致（例如分别用 Pa 和 m³，或 kPa 和 dm³ 等）。
Example: A gas occupies 200 cm³ at a pressure of 100 kPa. At constant temperature, if the volume is reduced to 100 cm³, the new pressure will be:
示例：某气体在 100 kPa 压强下占据 200 cm³ 的体积。在恒温下，若体积减小到 100 cm³，新的压强将为：
p₂ = (p₁V₁)/V₂ = (100 kPa × 200 cm³) / 100 cm³ = 200 kPa
7. Explaining Boyle’s Law with the Particle Model | 用粒子模型解释玻意耳定律
Why does pressure increase when volume decreases? Imagine a sealed container with a piston. When the volume is halved, the same number of particles are squeezed into half the space. The particles will hit the walls twice as often per second, because they have half the distance to travel between collisions. Since pressure is caused by these collisions, doubling the collision frequency doubles the pressure.
为什么体积减小时压强会增大？设想一个带有活塞的密封容器。当体积减半时，同样数量的粒子被挤压到一半的空间中。粒子每秒撞击壁面的频率变为原来的两倍，因为它们在两次碰撞之间移动的距离减半。由于压强是由这些碰撞引起的，碰撞频率加倍就使压强加倍。
The particles do not change speed (temperature is constant), and the force per collision is the same. Only the frequency of collisions changes, so pressure rises in exact inverse proportion to volume.
粒子的速度不变（温度恒定时），每次碰撞的力度也保持不变。只有碰撞频率发生变化，因此压强以精确的反比关系随体积变化。
8. Effect of Temperature on Pressure | 温度对压强的影响
When a gas is heated while the volume is held constant, the particles gain kinetic energy. They move faster, and each collision with the wall delivers a larger force. In addition, the higher speed means particles cross the container more quickly, leading to more frequent collisions. Both effects combine to increase the pressure.
当气体受热而体积保持不变时，粒子获得动能。它们运动速度加快，每次与壁面的碰撞力度更大。此外，更高的速度意味着粒子穿过容器的速度更快，导致碰撞更频繁。这两种效应共同作用，使压强升高。
For a constant volume, the relationship between pressure and absolute temperature (in kelvin) is directly proportional: p/T = constant, provided the mass of gas is fixed. This is sometimes called the pressure law. At absolute zero (0 K, –273 °C), particles have minimum kinetic energy and pressure would theoretically be zero.
在恒定体积下，压强与绝对温度（开尔文）成正比关系：p/T = 常数，前提是气体质量固定。这有时被称为压强定律。在绝对零度（0 K，–273 °C）下，粒子的动能最低，理论上的压强为零。
9. Real‑World Applications | 实际应用
Understanding gas pressure helps explain many everyday phenomena:
理解气体压强有助于解释许多日常现象：
- A bicycle pump – as you push the handle, you compress the air inside, increasing its pressure so it flows into the tyre.
- Aerosol cans – the propellant gas is compressed to a high pressure; when the nozzle is pressed, gas rushes out because of the pressure difference.
- Scuba diving – as divers descend, water pressure increases, compressing air in buoyancy devices and lungs; divers must balance pressures to avoid injury.
- Weather and tyres – car tyres are inflated to a specific pressure because under‑inflation or over‑inflation affects safety and fuel efficiency.
- 打气筒——当你推动手柄时，压缩筒内空气，使其压强升高，从而气流进入轮胎。
- 喷雾罐——推进气体被压缩到高压状态；按下喷嘴时，由于压差，气体喷出。
- 水肺潜水——随着潜水员下潜，水压增大，压缩浮力装置和肺中的空气；潜水员必须平衡压力以避免伤害。
- 天气与轮胎——汽车轮胎充气至特定压强，因为充气不足或过度都会影响安全性和燃油效率。
In medical devices like ventilators, controlling gas pressure is vital for patient breathing support.
在呼吸机等医疗设备中，控制气体压强对维持病人呼吸至关重要。
10. Investigating Boyle’s Law Experimentally | 实验探究玻意耳定律
A typical school experiment uses a sealed syringe connected to a pressure sensor. By pushing the plunger to change the volume and reading the corresponding pressure, students can record a series of p and V values. Plotting pressure against 1/V yields a straight line through the origin, confirming the inverse relationship.
典型的学校实验使用一个密封的注射器连接压力传感器。通过推动活塞改变体积并读取相应的压强，学生可以记录一系列 p 和 V 值。将压强对 1/V 作图会得到一条过原点的直线，从而证实反比关系。
Alternatively, a Bourdon gauge attached to a compressed gas cylinder can be used. The key points for a valid experiment are: keep the temperature constant (allow time for the gas to return to room temperature after compression), use dry air, and ensure no gas leaks. Always wear eye protection.
也可以使用连接在压缩气瓶上的布尔登压力计。确保实验有效性的关键点是：保持温度恒定（压缩后给予气体时间恢复室温），使用干燥空气，并确保没有气体泄漏。务必佩戴护目镜。
11. Common Misconceptions | 常见误区
Misconception 1: ‘Pressure and volume are directly proportional.’ Correction: They are inversely proportional at constant temperature. Doubling volume halves pressure.
误区 1： “压强与体积成正比。” 更正：在恒温下它们成反比。体积加倍，压强减半。
Misconception 2: ‘Gas particles expand when heated.’ Correction: The particles themselves do not expand; they gain kinetic energy and move faster, occupying a larger space because they push outward more vigorously.
误区 2： “气体粒子受热会膨胀。” 更正：粒子本身不会膨胀；它们获得动能并运动得更快，因为更有力地向外推挤而占据更大的空间。
Misconception 3: ‘Pressure decreases when a container is cooled because the particles shrink.’ Correction: Particles do not shrink; their kinetic energy decreases, they move slower, and collisions become less frequent and less forceful.
误区 3： “冷却容器时压强降低是因为粒子缩小了。” 更正：粒子并不缩小；它们的动能减少，运动变慢，碰撞频率和力度都下降。
Misconception 4: ‘Boyle’s law works for liquids.’ Correction: Boyle’s law applies only to gases. Liquids are almost incompressible, so their volume does not change significantly with pressure.
误区 4： “玻意耳定律适用于液体。” 更正：玻意耳定律仅适用于气体。液体几乎不可压缩，因此其体积几乎不随压强变化。
12. Summary and Key Points | 总结与关键点
Gas pressure is caused by particle collisions with container walls. Boyle’s law (pV = constant) describes the inverse relationship between pressure and volume at constant temperature. Using the particle model, we can explain how changes in volume, temperature, and amount of gas affect pressure. This understanding is used in countless technologies and natural phenomena.
气体压强是由粒子与容器壁的碰撞产生的。玻意耳定律（pV = 常数）描述了恒温下压强与体积的反比关系。利用粒子模型，我们可以解释体积、温度和气体量的变化如何影响压强。这一理解被广泛应用于无数技术与自然现象中。
Key formulas:
关键公式：
pV = constant p₁V₁ = p₂V₂ pressure = force ÷ area
Remember to use Kelvin for temperature in gas law calculations, and always check that units are consistent.
请记住在气体定律计算中使用开尔文温度，并始终检查单位是否一致。
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