1What's really going on in the glass
Two ideas: water tugs, and grains hold on
You only need two ideas. Watch each one move:
Water is a tugging crowd
Water is millions of tiny jiggling pieces (molecules). They never hold still, and each one has a slightly sticky side. They bump and tug on anything you drop in.
A grain is held by a grip
A powder is millions of tiny grains stuck together. To pull a grain off the pile, something has to grab it harder than the pile is holding it back.
2Two kinds of grain
"Grabs water back" vs "only grabs itself"
The two powders look alike, but their grains play tug-of-war in opposite ways:
Grabs water back
A sugar grain is sticky to water. When water tugs, the grain hugs back — so water can peel it off and carry it away.
Only grabs itself
A sand grain grips its own pieces super tight and ignores water. Water tugs, but it can't get a grip strong enough to peel a grain off.
3Your turn — pull on one grain
Zoom way in and stir the water harder
Here's one sugar grain up close, with the water crowd around it. Slide to stir harder — watch the water molecules cluster on the grain and start peeling its tiny pieces away. The harder they tug, the faster pieces let go.
give it a stir →
4Now the real test
The sugar vanishes — but where did it go? 🥄
You already know the sugar disappears and the sand sits. Here's the real puzzle: once the sugar is gone from sight, is it gone for good, or still hiding in the glass? Guess first, then drop them in and watch.
Guess before you drop them in
The sugar grains vanish into the water until you can't see a single one. So where did the sugar go?