Science in Punggol study guide · Article 0013 of 20
The water cycle connects evaporation, condensation, precipitation and the movement of water. Liquid water becomes invisible water vapour during evaporation. Water vapour becomes liquid droplets during condensation.
These processes explain familiar observations, from a drying puddle to droplets outside a cold bottle.
On this page: Evaporation can happen below boiling point · Condensation forms liquid droplets · Connect the processes in the environment · Worked question: droplets outside a container
Evaporation can happen below boiling point
Evaporation occurs at the surface of liquid water. Water does not have to boil to evaporate. A wet cloth dries at room temperature because water evaporates from it into the air.
Warmer conditions, moving air and a larger exposed surface can increase evaporation when other relevant conditions are comparable. Humidity also affects drying. A fair investigation changes one selected condition while keeping the others as similar as possible.
For example, compare equal starting volumes of water in containers with different exposed surface areas. Keep their location and other relevant conditions the same. Record how much water remains after the same duration.
Water vapour is invisible. Visible mist, sometimes called steam, consists of tiny liquid droplets formed when water vapour cools and condenses. What we can see and what is present are not always the same.
Condensation forms liquid droplets
When moist air meets a sufficiently cold surface, water vapour can lose heat and condense into liquid water. This explains droplets appearing on the outside of a cold drink container.
The water comes from vapour in the surrounding air. In an intact, sealed container, it has not travelled through the wall from the drink. The cold surface provides the conditions for condensation.
A process name alone is not a full explanation. “Condensation happened” needs a source of water vapour and the cooling that caused it to become liquid.
Connect the processes in the environment
Water evaporates from exposed surfaces. In the atmosphere, cooling can cause water vapour to condense into tiny droplets that form clouds. When droplets become large enough, they can fall as rain.
Water then collects, flows over land or enters the ground. Evaporation continues from suitable surfaces. A water-cycle diagram links these processes; it does not show one fixed route or timetable for every drop.
After rain in Punggol, a puddle may become smaller through evaporation, drainage or water entering the ground. Read the surface conditions before deciding which process explains a particular observation.
Worked question: droplets outside a container
Question: A dry, sealed container of cold water is placed on a table. Droplets later appear on its outside. Where did the droplets come from, and how did they form?
Worked explanation: The water came from water vapour in the surrounding air. The cold surface cooled nearby water vapour, causing it to lose heat and condense into liquid droplets on the container.
Common mistake: “The cold water leaked through the container.” That conflicts with the stated sealed-container condition. The explanation must account for water vapour outside the container.
To review the concept, draw liquid water and water vapour with arrows between them. Label evaporation and condensation, then explain what conditions support each change.
