💧 HUMIDITY: HOW MUCH WATER IS IN THE AIR?
PAGE 1 OF 5, INVISIBLE WATER IN THE SKY
NOT A CLOUD YET
HUMIDITY = WATER VAPOUR IN AIR
On a clear day the sky looks empty, but the air is full of water vapour: tiny water molecules floating as gas. You cannot see them. Humidity tells us how much of that invisible water is mixed into the air. Topic 7 (Temperature) showed how the Sun heats land and sea and drives evaporation from puddles, lakes, oceans, and wet soil. That heated water escapes as vapour and joins the atmosphere. More vapour often means the air feels stickier and sweat is slower to dry. Less vapour feels crisp and dry, even at the same thermometer reading.
👁 SEE vs FEEL
Clear humid air still looks see-through. You notice humidity when your skin feels damp, hair frizzes, or windows fog up later.
STEAM!
KETTLE
💨 Boiling water sends vapour upward, the same kind of invisible gas that mixes into outdoor air.
🌊 Oceans and lakes evaporate constantly, even when you do not see bubbles or steam clouds.
🌊 Oceans and lakes evaporate constantly, even when you do not see bubbles or steam clouds.
DRY DAY
🏜 Desert air can feel dry because it holds far less water vapour than air near a warm ocean.
🧴 Low humidity lets sweat evaporate fast, which cools your skin more quickly on a hot day.
🧴 Low humidity lets sweat evaporate fast, which cools your skin more quickly on a hot day.