What properties do solids, liquids and gases have? Material processes - Solids, liquids and gases - Solids Learning Points Solids have a fixed shape that can only be changed by external force. Solids have a fixed volume. The molecules in a solid are tightly packed together. A Twig Curriculum Film. Delivering key learning points. Get straight to the facts in just three minutes – directly linked to core learning, Twig's curriculum films will fit neatly into your lesson plans.