ScienceGrade 3

Why Does Water Form Outside a Cold Glass? Condensation for Kids

The air around you holds invisible water in gas form — water vapor — right now.

Learning Objective

Students will learn that the "sweat" on a cold glass is NOT a leak — invisible water vapor in the air touches the cold surface, loses energy, and turns back into liquid droplets — condensation — and that the same process makes dew on grass, fog on a bathroom mirror, and the droplets inside clouds (TEKS 3.6B — water changes state between liquid and gas).

What You'll Learn

When water vapor touches a COLD surface, it loses energy and turns back into
The droplets come from the AIR, not through the glass — the glass never leaks.
Only cold surfaces collect it — a room-temperature glass stays dry in the same room.
Dew on morning grass, fog on the bathroom mirror, and tiny droplets that build

Words to Know

Water vapor: Water in invisible gas form, floating in the air.; Water vapor is in the air around you right now.
Condensation: Water vapor turning back into liquid droplets on a cold surface.; Droplets beading on the cold glass are condensation.
Gas: A state of matter that spreads out to fill any space — invisible.; Water vapor is a gas mixed into the air.
Dew: Morning water drops that condensed on cold grass overnight.; Dew makes the grass sparkle at sunrise.
Seal: Closed tight so nothing can get in or out.; The sealed cup proves the water came from the air.

Check What You Learned

Quick Quiz

1 / 5

Where does the water on the outside of a cold cup really come from?

Fun Facts

Air contains water vapor — water in its invisible gas state — added constantly by evaporation, breath, and living things
Source: NGSS 2-PS1 / 5-ESS2-1, water cycle and states of matter
When water vapor contacts a surface colder than the air's dew point, it loses energy and condenses into liquid droplets on that surface — this is condensation
Source: standard physical-science curricula / NOAA dew-point materials
The droplets on a cold glass come from the surrounding air, NOT through the glass — a sealed cup still collects exterior condensation, and weighing a sweating glass shows it gaining mass from the air
Source: classic classroom condensation demos
Only the cold surface collects droplets: an ice-cold glass and a room-temperature glass in the same room show condensation on the cold one only — the cold is the collector
Source: standard condensation experiments
Dew on grass, fog on a bathroom mirror or cold window, and the droplets that form clouds are all condensation — vapor cooling into liquid
Source: NOAA / standard earth-science curricula
Warm air can hold more water vapor than cold air — which is why humid summer days make cold drinks "sweat" faster
Source: standard meteorology, Clausius relationship simplified

Lesson Info

Grade 3

Standards Alignment

TEKS 3.6B
describe and classify samples of matter as solids, liquids, and gases and demonstrate that matter can change state by heating and cooling
2-PS1-1
describe and classify materials by observable properties; NGSS 5-ESS2-1: the water cycle (condensation's role)