📊 AIR PRESSURE
PAGE 1 OF 5, THE SKY HAS WEIGHT
NOT "EMPTY"
AIR PRESSURE = FORCE OF THE WHOLE COLUMN
Air is made of molecules with mass — and gravity pulls them toward Earth. At any spot on the ground, the air pressure is the weight of all the air in a column above a square of surface (plus tiny correction for motion — but think "weight of stack" first). Mean sea level is often near 1013 hPa (hectopascals) — about 1 kilogram of force on every square centimetre if you average — roughly ten tonnes of air on an area about the size of a small car parking spot — that is the hub's 10 tonnes per square metre story! You do not feel crushed because pressure balances inside your body and outside.
🧪 UNITS
Meteorologists use hectopascals (hPa) = millibars. Same number, just two names. Older TV might say "inches of mercury" for barometers — same idea, different ruler.
PUSH!
1013
Average sea-level pressure: familiar baseline for "normal" maps
BALANCE
Eardrums, lungs, and buildings: inside pressure ≈ outside