A root beer float is a combination of root beer, ice cream and foam.
The three states are:
a) Root beer is a liquid wherein the particles move freely and tend to take the shape of the container.
b) Ice cream is a solid in which the particles have a fixed shape and held strongly in place. Unlike liquids, solids retain their shape.
c) Foam is a gas which is produced by the reaction of root beer with the ice cream. Gas particles move quickly and fill the container they occupy.