Lower secondary · 10 min

Solids, liquids, gases: a particle view

Cool the particle box and squeeze the piston to compress a gas into the packing of a liquid, then a solid.

Goal

Relate temperature, volume and particle spacing to the three states of matter and to density $\rho = m/V$ .

Apparatus and reagents

Simulated particle box with piston (no chemicals), thermometer and volume scale.

Procedure

Set $T = 600$ K and a large volume: the particles fly fast and fill the whole box — the gas state.
Push the piston to a small volume while keeping T high: same particles, much closer together — a compressed gas.
Now lower the temperature: the particles slow down and jostle in a dense crowd — approaching the liquid and solid pictures.
Compare the three settings and rank the states by density and by freedom of motion.

What to observe

At high T and large V the particles are far apart and fast; shrinking V crowds them into a smaller space.
At low T the particles move slowly and stay clustered — the same number of atoms in a much denser arrangement.

Explanation

In a gas the particles are far apart and move freely; in a liquid they are close but can still slide past each other; in a solid they occupy fixed positions. Because density is $\rho = m/V$ , compressing the same mass into a smaller volume raises the density — solids and liquids are far denser than gases.