Phases of Matter

In the solid phase the molecules are closely bound to one another by molecular forces. A solid holds its shape and thevolume of a solid is fixed by the shape of the solid.

In the liquid phase the molecular forces are weaker than in a solid. A liquid will take the shape of its container with a free surface in a gravitational field. In microgravity, a liquid forms a ball inside a free surface. Regardless of gravity, a liquid has a fixed volume.

In the gas phase the molecular forces are very weak. A gas fills its container, taking both the shape and the volume of the container.

The three normal phases of matter listed on the slide have been known for many years and studied in physics and chemistry classes. In recent times, we have begun to study matter at the very high temperatures and pressures which typically occur on the Sun, or during re-entry from space.