Ruby’s Window Drops

Ruby finds tiny drops on the inside of the kitchen window. Outside, the garden is cold and still. “Has rain come through the glass?” she asks Dad. The window is shut, and its frame feels dry. They look for another explanation before blaming a leak.

Ruby wipes a clear patch with a clean cloth. After a while, small droplets appear there again. Dad explains that air contains water vapour, a gas they cannot see. When some water vapour cools against the cold glass, it can change into liquid water.

“Can we make that happen somewhere else?” Ruby asks. They set two dry metal cups on a tray. Dad puts ice water in one and room-temperature water in the other. Neither cup is filled to the rim. Ruby checks that both outsides begin completely dry.

After several minutes, droplets gather on the outside of the colder cup. The other stays mostly dry. Ruby has not poured water down either side. Water vapour from the surrounding air has cooled at the cold surface. This change from gas to liquid is called condensation.

Ruby records their observation before touching the cups. The comparison supports the cold-surface explanation, but she checks for spills too. “A wet outside does not always mean a leaking cup,” she says. They must consider what happened, rather than choosing a cause from appearance alone.

Through the window, clouds drift over the garden. Clouds contain tiny water droplets or ice crystals. They are not simply clouds of invisible water vapour. Dad explains that condensation is part of the water cycle, along with evaporation and water returning to the ground as precipitation.

They compare the cup droplets with the window drops. Both formed where moist air met a cold surface. Dad opens the ventilation latch to help moist indoor air escape. They will watch other mornings instead of expecting one small opening to solve every damp problem.

Ruby dries the window ledge and puts her cup drawings on the table. “The water was already in the air,” she says. Her first idea about rain did not fit all the evidence. Now a misty window reminds her of a journey from invisible vapour to visible drops.