Explain evaporation and condensation using observations

Learning goal: Investigate how liquid water can become water vapor in air and how water vapor can become liquid droplets. Water vapor is water in its gas form and is invisible. Visible mist, fog and the white material in many clouds consist of tiny droplets or ice particles, not visible individual water-vapor gas.

Place a shallow amount of water in an adult-selected stable container and mark the starting level. Observe it again later without drinking from it or moving water in or out. If the level decreases and spilling or leaking has been ruled out, evaporation is a possible explanation. During evaporation, liquid water becomes water vapor and enters the surrounding air.

Evaporation can happen below the boiling point. A puddle or wet cloth can dry in ordinary conditions. Water needs energy to evaporate. Sunshine or warm air can supply that energy, which is one reason a puddle often dries faster on a warm, sunny day. A wet surface can feel cool as it dries, because evaporation takes energy from the water left behind. Temperature, exposed surface, moving air and moisture already in the air can affect the rate, so compare one changed condition at a time when planning an investigation. This lesson does not require boiling water.

For condensation, an adult places cold water or ice water in a sound, transparent cup and dries the outside. Watch for droplets forming on the outer surface. Water vapor in the surrounding air can cool near the cold surface and change to liquid droplets. Those droplets did not have to leak through the cup wall or be painted onto it.

The diagram distinguishes liquid water inside the cup from newly formed droplets outside it. Labeled arrows in the surrounding space represent the invisible vapor and its change conceptually; they are not visible trails of gas. Read that explanation before interpreting the picture as a photograph. A model can represent something unseen, but must say what its symbols stand for.

Evaporation and condensation describe opposite changes between liquid water and water vapor. They do not change water into a different substance. Water can also freeze or melt, as studied earlier, but freezing into solid ice is not the same change as condensing into liquid droplets. Name the starting and ending forms before choosing the process word.

Water in the atmosphere helps form clouds and fog when tiny droplets or ice particles develop under suitable conditions. Rain involves droplets that become large enough to fall; cooling does not mean every bit of water vapor immediately becomes rain at the ground. Snow, sleet and hail are frozen forms of water that fall from clouds; they involve additional freezing and growth processes.

Clouds can also be connected with the weather you notice. Look at the sky and record what the clouds look like, then record the weather that happens. Thick, dark gray clouds that cover the sky often come with or before rain or snow. Scattered white, puffy clouds with blue sky between them often come with dry weather, and thin, wispy white clouds high in the sky usually do not bring rain that day. Fog is a cloud that forms at ground level, so it makes it hard to see far. These are common patterns, not promises: a dark cloud can pass without rain. You do not need to learn the names of cloud types; describe what the clouds look like and what weather came with them. At this grade, connect actual evaporation and condensation observations with atmospheric water instead of memorizing a decorative cycle diagram without understanding the changes.

Worked example 1: Explain a lower level carefully. The marked water level is lower after a day, and the container was not tipped, used or found leaking. Evaporation is supported as an explanation. A lower level alone would not rule out a spill if nobody checked what happened.

Worked example 2: Locate the droplets. Water drops appear on the outside of a cold cup that was initially dry. Describe their outside location and connect them with condensation from surrounding water vapor. Do not claim the cup manufactured new water.

Worked example 3: Name the change. Liquid to vapor is evaporation. Vapor to liquid droplets is condensation. Liquid to solid ice is freezing. Sorting by the starting and ending forms prevents treating every cooling change as freezing.

Guided investigation: Record the initial and later water level in one evaporation setup, and observe a separate cold-cup condensation demonstration. Use drawings with labels inside, outside, liquid and vapor where appropriate. Mark actual observation times rather than inventing a smooth sequence that was never seen.

Independent tasks: Explain each investigation with the correct change word, distinguish invisible vapor from visible droplets and identify a possible alternative explanation for a lower water level. Use the model to show where condensation occurs without assuming its arrows are literal visible gas trails.

Feedback: If a learner calls visible fog water vapor, separate the invisible gas from the tiny droplets that scatter light. If they assume every droplet came through the cup, compare an intact dry cup before and after cooling under adult guidance. Require evidence and clear locations.