1What "warm" and "drying" really are
Heat is jiggle — and the fastest jigglers fly away
You only need two ideas. Watch each one move:
Warm = fast jiggling
A liquid is a crowd of tiny molecules, always jiggling. The faster they jiggle, the warmer it is. Heat isn't a thing inside — heat is the jiggle.
The fastest ones escape
Now and then a super-fast jiggler at the top leaps into the air. That's a drop drying. And the fastest one leaving means the crowd left behind is a little slower — a little cooler.
2Two kinds of puddle
The clingy puddle vs the runaway puddle
Not every liquid lets its molecules leave at the same speed. Here are the two extremes, side by side:
The clingy puddle
Molecules hold on tight. Only a few escape, slowly — so it dries slowly and barely cools.
The runaway puddle
Molecules barely hold on. They leap off in a rush — so it dries fast and carries away lots of heat.
3Your turn — turn up the warmth
Make the molecules jiggle and watch some fly off
Here's one puddle, up close. Slide the warmth up and watch the molecules jiggle faster — and more of the speedy ones escape off the top. Keep an eye on the puddle's own temperature as they leave.
4Now the real test
Where does the alcohol's cold actually come from? 🧴💧
Two drops sit on the back of a hand — one water, one alcohol. The alcohol will feel icy. But why? Is the alcohol drop already colder than the water to start with — or do they start the same, and the cold gets made only as it dries? Guess first, then drop a thermometer in each and let them dry.
Guess before you dry them
The alcohol will feel freezing. But where's that cold coming from — is the alcohol drop already colder than the water, or do they start the same and the chill only appears as it dries?