Introduce the process of condensation. If students do not know what the process of condensation is, you can tell them it is the opposite of evaporation. In evaporation, a liquid (like water) changes state to become a gas (water vapor). In condensation, a gas (like water vapor) changes state to become a liquid (water). Explain that as water molecules in the air cool and slow down, their attractions overcome their speed and they join together, forming liquid water. This is the process of condensation.