States of matter, gas pressure and Boyle's law

Last time

Before we start: last time, in Particles, states of matter and gas pressure, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Three states, one idea

Ice, water and steam are all made of the same particles. The only difference is how those particles are arranged, and how they move. With that one idea we can explain solids, liquids, gases, and even why a gas pushes on its container.

Solid, liquid, gas

In a solid the particles are packed tightly, in a regular pattern, and they only vibrate on the spot. In a liquid they are still touching, but jumbled up, and they slide past each other. In a gas the particles are far apart and fly about randomly at high speed.

Solids

In a solid, the particles are close together, in a regular pattern, held by strong forces. They cannot move around. They only vibrate about fixed positions. So a solid keeps its own shape and its own volume, and it cannot be squashed. It has a high density, because the particles are so close.

Liquids

In a liquid, the particles are close together, but in a random, jumbled arrangement. They slide past each other, held by forces weaker than in a solid. So a liquid has a fixed volume, but it flows and takes the shape of its container. It is also very hard to squash, and its density is almost the same as the solid's.

Gases

In a gas, the particles are far apart, with almost no forces between them. They move at high speed in random directions, in straight lines until they collide. So a gas has no fixed shape and no fixed volume. It fills any container. It can be squashed easily, and its density is very low.