📚 IGCSE Physics: Properties of Solids, Liquids and Gases | IGCSE物理：固液气三态的性质
Matter exists in three familiar states: solid, liquid and gas. In the Edexcel IGCSE Physics course, the particle model is used to explain the characteristic properties of each state, including shape, volume, density and compressibility.
物质通常以三种状态存在：固态、液态和气态。在爱德思 IGCSE 物理课程中，我们用粒子模型来解释各状态的特征性质，包括形状、体积、密度和可压缩性。
1. The Three States of Matter | 物质的三种状态
All substances can exist as a solid, a liquid or a gas, depending on temperature and pressure. Water is a familiar example: ice is solid, liquid water is a liquid, and steam is a gas.
所有物质都可以随温度和压强的变化而处于固态、液态或气态。水是常见例子：冰是固态，液态水是液态，水蒸气是气态。
A solid has a fixed shape and a fixed volume.
固体具有固定的形状和体积。
A liquid has a fixed volume but takes the shape of its container.
液体具有固定体积，但形状随容器而变。
A gas has neither a fixed shape nor a fixed volume.
气体既没有固定形状，也没有固定体积。
2. The Particle Model | 粒子模型
The kinetic particle model represents every substance as tiny particles, such as atoms, molecules or ions, in constant motion. The arrangement and movement of these particles explain the observable properties of each state.
分子动理论把每种物质视为不断运动着的微小粒子，例如原子、分子或离子。这些粒子的排列与运动方式可以解释各状态的可观察性质。
Particles are very small and cannot be seen with an optical microscope.
粒子非常小，用光学显微镜无法看到。
There are spaces between particles, and the strength of forces between them depends on the state.
粒子之间存在空隙，粒子间作用力的大小取决于物态。
Heating a substance increases the kinetic energy of its particles.
加热物质会增加粒子的动能。
3. Properties of Solids | 固体的性质
In a solid, particles are packed closely together in a regular arrangement. They vibrate about fixed positions but do not move from place to place.
在固体中，粒子紧密排列，通常具有规则的排列结构。它们只能在固定位置附近振动，不能从一个位置移动到另一个位置。
Fixed shape and volume: strong forces of attraction hold the particles in place.
固定形状和体积：强吸引力把粒子固定在位置上。
Not easily compressed: there is very little empty space between particles.
不易被压缩：粒子之间空隙很小。
Diffusion is extremely slow at ordinary temperatures because particles cannot flow past one another.
常温下扩散极慢，因为粒子不能相互滑过。
Density is usually high compared with a gas, because mass is contained in a small volume.
与气体相比密度通常较高，因为质量集中在很小的体积内。
4. Properties of Liquids | 液体的性质
In a liquid, particles are close together but their arrangement is irregular. They have enough energy to slide past each other, which allows the liquid to flow.
在液体中，粒子距离很近，但排列不规则。粒子有足够能量相互滑过，因此液体能够流动。
Fixed volume: particles are close, so a liquid cannot be compressed easily.
体积固定：粒子密集，所以液体不容易被压缩。
No fixed shape: particles can move over each other, so the liquid takes the shape of the bottom of its container.
形状不固定：粒子可以相对滑动，因此液体呈现容器底部的形状。
Density is close to that of the solid, but usually slightly lower.
密度与固体接近，但通常略低。
Diffusion can occur because particles are able to move throughout the liquid.
液体中会发生扩散，因为粒子能在液体中运动。
5. Properties of Gases | 气体的性质
In a gas, particles are far apart and move quickly in random directions. The forces of attraction between particles are very weak.
在气体中，粒子相距很远，向各个方向快速随机运动。粒子之间的吸引力非常弱。
No fixed shape or volume: gas expands to fill all available space.
没有固定形状或体积：气体会膨胀并充满所有可用的空间。
Very compressible: there are large empty spaces between particles.
极易被压缩：粒子之间有大量空隙。
Low density: the same number of particles occupies a much larger volume than a liquid.
密度低：与液体相比，同样数量的粒子占据大得多的体积。
High rate of diffusion: random fast motion allows gas particles to spread quickly.
扩散速率高：快速无规则运动使气体粒子能迅速散开。
Gas pressure is caused by particles colliding with the walls of the container.
气体压强是由粒子撞击容器壁产生的。
6. Density and Compressibility | 密度与可压缩性
Density tells us how much mass is packed into a unit volume. The equation is:
密度表示单位体积内所含质量的多少。公式为：
ρ = m / V
mass in kg, and V is volume in m³. For IGCSE you may also use g/cm³; 1 g/cm³ = 1000 kg/m³.
式中 ρ 为密度，单位 kg/m³；m 为质量，单位 kg；V 为体积，单位 m³。在 IGCSE 中也可使用 g/cm³；1 g/cm³ = 1000 kg/m³。
In a solid or liquid, particles are packed closely, so the density is usually much higher than in a gas. Because the particles in a gas are far apart, gases have low density and can be compressed easily. Solids and liquids are almost incompressible.
在固体或液体中，粒子排列紧密，因此密度通常远高于气体。由于气体粒子相距很远，气体密度低且容易压缩。固体和液体几乎不可压缩。
7. Diffusion in Liquids and Gases | 液体和气体中的扩散
Diffusion is the spreading out of particles from a region of higher concentration to a region of lower concentration due to their random motion. It happens in liquids and gases, but is very slow in solids at ordinary temperatures.
扩散是指粒子因无规则运动而从高浓度区域向低浓度区域散开的过程。扩散发生在液体和气体中；在常温下，固体中扩散极慢，几乎观察不到。
In air, the smell of perfume spreads because gas particles mix by diffusion.
在空气中，香水气味扩散，是因为气体粒子通过扩散相互混合。
In water, a crystal of potassium manganate(VII) slowly produces a purple colour as its particles diffuse.
在水中，高锰酸钾晶体慢慢产生紫色，是因为其粒子扩散。
The rate of diffusion increases with temperature because particles have more kinetic energy.
温度升高，扩散速率增大，因为粒子动能更大。
Lighter particles diffuse faster than heavier particles at the same temperature.
相同温度下，较轻的粒子比重的粒子扩散更快。
8. Changes of State | 物态变化
A substance changes state when energy is transferred to it or away from it. These are physical changes, not chemical changes, because the particles themselves remain the same.
当物质吸收或放出能量时，就会发生物态变化。这些变化是物理变化而不是化学变化，因为粒子本身没有改变。
Melting: solid → liquid, energy is absorbed.
熔化：固态 → 液态，吸收能量。
Freezing: liquid → solid, energy is released.
凝固：液态 → 固态，放出能量。
Evaporation: liquid → gas at the surface, below the boiling point.
蒸发：液态 → 气态，发生在液体表面，温度低于沸点。
Boiling: liquid → gas throughout the liquid.
沸腾：液态 → 气态，发生在液体内部和表面。
Condensation: gas → liquid, energy is released.
凝结：气态 → 液态，放出能量。
Sublimation: solid → gas directly, energy is absorbed.
升华：固态直接 → 气态，吸收能量。
During a change of state, the temperature stays constant even though energy is still being transferred. This energy is used to change the arrangement of particles or to overcome forces between them.
在物态变化过程中，即使能量持续传递，温度仍保持不变。这些能量用于改变粒子的排列或克服粒子间的作用力。
9. Latent Heat and the Kinetic Theory | 潜热与分子
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