What are the three main points of the particle theory of expansion and contraction?

The particle theory of expansion and contraction states that matter is composed of tiny particles that are constantly in motion. When a substance is heated, the particles gain energy and move faster, causing them to spread apart and the substance to expand. Conversely, when a substance is cooled, the particles lose energy, move slower, and come closer together, leading to contraction. This behavior is consistent across solids, liquids, and gases, though the extent of expansion and contraction varies by state and material.