Field notes: water on the move

Matter has mass and takes up space. In a solid, particles are packed close together and vibrate in fixed positions, so the solid keeps its own shape. In a liquid, particles stay close but can move past one another; a liquid flows and takes the shape of its container. In a gas, particles are much farther apart and move freely, spreading out to fill available space. Heating or cooling can change a substance’s state. When liquid water gains enough energy, it evaporates into invisible water vapour. When water vapour cools, it condenses into liquid droplets. Freezing changes liquid water to solid ice; melting changes ice to liquid water. The substance is still water through these changes.