Particles of Matter

Core concept

The constant motion of particles explains diffusion — the spreading of one substance through another, like the smell of perfume gradually filling a room as its particles spread out and mix with air particles. Particle motion increases with temperature, which is why diffusion happens faster in hot liquids or gases than in cold ones. The spaces between particles explain why gases can be compressed easily (like squeezing air into a smaller container), while solids and liquids, with much less space between particles, are far harder to compress.