📚 Explaining Gas Pressure | 解释气体压强
Gas pressure is one of the most important ideas in the particle model of matter. It explains why a balloon stays firm, why a bicycle tyre supports your weight, and why a sealed can of air can burst if it is heated too much. In this article, we will build a clear picture of gas pressure using only simple particle ideas at KS3 level.
气体压强是物质粒子模型中最重要的概念之一。它解释了为什么气球能保持鼓胀、为什么自行车轮胎能支撑你的体重，以及为什么密封的空气罐受热过多时可能会爆裂。本文将只用 KS3 阶段简单的粒子观点，帮助你清晰理解气体压强。
1. What is a gas? | 什么是气体？
A gas is a state of matter in which particles are far apart and move freely at high speed. Unlike solids and liquids, gases have no fixed shape or fixed volume. They spread out to fill any container they are placed in.
气体是物质的一种状态，其中的粒子相距很远，并以高速自由运动。与固体和液体不同，气体没有固定的形状，也没有固定的体积。气体会扩散并充满所置入的任何容器。
The particles in a gas move in straight lines until they hit something, such as the wall of the container or another particle. When they hit, they bounce off and change direction. This constant, random motion is the key to understanding gas pressure.
气体中的粒子沿直线运动，直到撞到某个物体（例如容器壁或另一个粒子）。碰撞后，它们会弹开并改变方向。这种持续不断的无规则运动是理解气体压强的关键。
2. Collisions create pressure | 碰撞产生压强
When gas particles collide with the walls of their container, each collision pushes on the wall with a tiny force. One collision is far too small to notice, but across the whole inner surface there are billions and billions of collisions every second.
当气体粒子与容器壁碰撞时，每次碰撞都会对器壁施加一个极小的力。一次碰撞小到无法察觉，但整个内表面每秒会发生数十亿、数百亿次碰撞。
The combined effect of these collisions is a steady outward push on the inside of the container. This push, spread over an area, is called gas pressure. The unit of pressure is the pascal (Pa), and one pascal is equal to one newton of force spread over one square metre.
这些碰撞的合效果是对容器内部产生持续向外的推力。这种分布在一定面积上的推力就叫做气体压强。压强的单位是帕斯卡（Pa），1 帕斯卡等于 1 牛顿的力作用在 1 平方米的面积上。
pressure = force ÷ area
This simple equation reminds us that pressure is bigger when a force is applied over a smaller area. In a gas, the force comes from particle collisions, so more collisions or harder collisions mean more pressure.
这个简单公式提醒我们，当力作用在更小的面积上时，压强会更大。在气体中，这个力来自粒子的碰撞，因此碰撞越多或越剧烈，压强就越大。
3. The particle model of gas pressure | 气体压强的粒子模型
The particle model states that gas pressure is caused by particles colliding with surfaces. More frequent or harder collisions produce greater pressure. This allows us to explain changes in gas pressure by thinking about what happens to the particles.
粒子模型认为，气体压强是由粒子与表面碰撞产生的。碰撞越频繁或越剧烈，压强就越大。因此，我们可以通过思考粒子的变化来解释气体压强的变化。
Three factors mainly affect gas pressure: the speed of the particles, which is linked to temperature; the volume of the container; and the number of particles in a fixed volume. Changing any one of these factors changes how often and how hard the particles hit the walls.
影响气体压强的主要有三个因素：粒子的速度（与温度有关）、容器的体积，以及一定体积内的粒子数量。改变其中任何一个因素，都会改变粒子撞击器壁的频率和力度。
4. Temperature and gas pressure | 温度与气体压强
When a gas is heated, its particles gain kinetic energy and move faster. Faster particles hit the container walls harder and more often. If the volume of the container stays the same, the gas pressure increases.
当气体受热时，粒子获得动能，运动得更快。更快的粒子更频繁、更有力地撞击容器壁。如果容器体积保持不变，气体压强就会增大。
If a gas is cooled, the particles slow down. They collide less often and with less force, so the pressure decreases. This is why a balloon left in a cold room may look slightly deflated even though no air has escaped.
如果气体被冷却，粒子运动变慢。它们碰撞的次数减少，力度变小，因此压强降低。这就是为什么放在寒冷房间里的气球看起来会稍微变瘪，尽管并没有漏气。
Heating a sealed container of gas is dangerous because the pressure can rise until the container bursts. Cooling a gas in a sealed container reduces the pressure, and the container may even buckle inwards if the outside pressure becomes much greater.
加热密封容器中的气体很危险，因为压强会不断升高，直到容器爆裂。冷却密封容器中的气体会降低压强，如果外部压强远大于内部压强，容器甚至可能向内凹陷。
5. Pressure and volume: the squeeze effect | 压强与体积：挤压效应
If you reduce the volume of a gas by squeezing it into a smaller space, the same number of particles now has less room to move. They hit the walls more frequently because they do not travel as far between collisions.
如果把气体挤压到更小的空间中，从而减小其体积，相同数量的粒子活动空间变小。由于粒子在两次碰撞之间不需要走那么远，它们会更频繁地撞击器壁。
This means that decreasing the volume of a gas increases its pressure, as long as the temperature and the number of particles stay the same. Increasing the volume has the opposite effect: the pressure decreases because collisions become less frequent.
这意味着，在温度和粒子数量不变的情况下，减小气体体积会增大压强。增大体积则会产生相反的效果：由于碰撞频率降低，压强会减小。
You can feel this by pressing the plunger of a sealed syringe with your finger over the opening. The more you squeeze the air into a smaller volume, the harder it pushes back. This is not because the particles have changed, but because they now strike the plunger more often.
你可以用一个密封的注射器来感受这点：用手指堵住开口并推动活塞。你越把空气压缩到更小的体积，它往回推的力就越大。这不是因为粒子本身变了，而是因为它们现在更频繁地撞击活塞。
6. Number of particles and gas pressure | 粒子数量与气体压强
If you pump more air into a container of fixed volume, you increase the number of gas particles inside. More particles in the same space means more collisions with the walls every second, so the pressure rises.
如果你在体积固定的容器中打入更多空气，内部的气体粒子数量就会增加。同一空间内粒子越多，每秒与器壁的碰撞就越多，因此压强会升高。
This explains why a bicycle tyre becomes harder as you pump air into it. The volume of the tyre barely changes, but the number of air particles inside increases, so the pressure increases and the tyre feels firmer.
这就解释了为什么给自行车轮胎打气时它会越来越硬。轮胎的体积几乎不变，但内部空气粒子的数量增加，因此压强增大，轮胎摸起来更硬。
The same idea applies to blowing up a balloon. Each breath adds more particles to a nearly fixed volume, raising the pressure and stretching the rubber until the balloon is firm. Letting some particles escape lowers the pressure and the balloon deflates.
同样的道理也适用于吹气球。每一口气都在接近固定的体积中增加更多粒子，使压强升高，橡胶被拉伸，气球逐渐变硬。放出一些粒子会使压强降低，气球就会变瘪。
7. Atmospheric pressure explained by particles | 用粒子解释大气压强
The air around you is a gas, and it exerts pressure on every surface. Atmospheric pressure at sea level is about 100,000 Pa (100 kPa). The air particles are pulled towards Earth by gravity, so they are more concentrated near the surface.
你周围的空气是一种气体，它对每个表面都施加压强。海平面的大气压强约为 100 000 Pa（100 kPa）。空气粒子被地球引力拉向地面，因此在地表附近更加密集。
Higher up a mountain, the air is thinner: there are fewer air particles in each cubic metre. Fewer particles means fewer collisions with surfaces, so atmospheric pressure is lower at high altitude. This is why climbers find it harder to breathe and why some packaged foods swell on mountains.
在高山上，空气更稀薄：每立方米中的空气粒子更少。粒子越少，与表面的碰撞就越少，因此高海拔处的大气压强较低。这就是为什么登山者会觉得呼吸困难，以及为什么一些包装食品在山上会膨胀。
8. Everyday examples of gas pressure | 气体压强的日常实例
Gas pressure is all around us. In a balloon, the particles of air inside are colliding with the rubber wall. The outward pressure balances the inward pull of the stretched rubber plus the outside air pressure, so the balloon keeps its rounded shape.
气体压强无处不在。在气球里，内部空气粒子不断撞击橡胶壁。向外的压强与拉伸橡胶的向内拉力以及外部气压相平衡，因此气球保持圆形。
Aerosol cans contain gas under high pressure. The warning not to heat them is based on the particle model: heating increases the speed of the particles, raising the pressure inside until the can may burst. Even a sealed plastic bottle of air can feel much harder in a hot car for the same reason.
气雾罐内装有高压气体。不要加热气雾罐的警告正是基于粒子模型：加热会使粒子速度加快，内部压强升高，直到罐子可能爆裂。出于同样的原因，热车里密封的塑料空气瓶摸起来也会硬得多。
A sealed crisp packet can look puffed up on a plane because the cabin pressure is lower at high altitude. The gas inside the packet pushes outward more strongly than the surrounding air pushes inward, so the packet expands until a new balance is reached.
飞机上密封的薯片袋会鼓起来，因为高空中机舱气压较低。袋内气体向外推的力大于周围空气向内推的力，因此袋子会膨胀，直到达到新的平衡。
9. Common misconceptions about gas pressure | 关于气体压强的常见误区
Misconception: gas particles need a force to keep moving. In fact, particles continue moving in straight lines unless they collide with something. They do not need a continuous push to stay in motion.
误区：气体粒子需要力来维持运动。事实上，粒子在没有碰撞时沿直线持续运动，不需要持续的推力来保持运动。
Misconception: gas pressure is caused by air being ‘sucked’ into a space. Actually, pressure is a push. When the pressure outside is greater than inside, air is pushed in, not pulled or sucked.
误区：气体压强是由空气被 ‘吸’ 进某个空间造成的。实际上，压强是一种推力。当外部压强大于内部压强时，空气是被推进去的，而不是被拉进去或吸进去的。
Misconception: heating a gas makes its particles expand. The particles themselves do not grow larger. They move faster, and the gaps between them may increase if the container can expand. The particles keep the same size, but their energy changes.
误区：加热气体会使粒子膨胀。粒子本身并不会变大。它们运动得更快，如果容器可以膨胀，粒子之间的间距会增大。粒子的尺寸保持不变，改变的是它们的能量。
10. Pressure in a sealed container: a summary of particle links | 密封容器中的压强：粒子联系总结
In a sealed container, the number of gas particles does not change. The two variables you can change are temperature and volume. The particle model links them like this:
在密封容器中，气体粒子的数量不变。你可以改变的两个变量是温度和体积。粒子模型将它们如此联系起来：
- Heat the gas at constant volume: particles move faster, collisions are harder and more frequent, pressure rises.
- 体积不变时加热气体：粒子运动加快，碰撞更剧烈、更频繁，压强升高。
- Cool the gas at constant volume: particles move slower, collisions are weaker and less frequent, pressure falls.
- 体积不变时冷却气体：粒子运动减慢
Published by TutorHao | KS3 Chemistry Revision Series | aleveler.com
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