Many experiments supporting hypothesis lead to scientific theory . Useful for predictive value. Often depict theories in terms of models , using familiar objects to represent invisible ones. Neither a fixed volume nor a fixed shape. Liquid - Particles cling closely to one another.
Molecules can slip over one another to adjust to the shape of their container.
Solid - Particles are attached to one another in a regularly spaced network. Interconversion between phases. Energy absorbed in converting a solid to a liquid to a gas. According to composition and properties.