An epithelium always has on surface where the cells are exposed either to the external environment or to an internal passageway or cavity; this surface is called the free surface of the epithelium.

An epithelium always has on surface where the cells are exposed either to the external environment or to an internal passageway or cavity; this surface is called the free surface of the epithelium.

Gases cannot form a free surface on their own.

However, gases do have a free surface at the boundary between gas and liquid, such as the free surface of the sea, or the boundary between the liquid of a soft drink and each carbon dioxide bubble rising in it.

it is because a liquid is bounded by 3sides .thus it has only the upper free surface.

# Free surface water # Masses in separate locations # The body with free surface water is rotating.