1Two ideas you'll need
Water hates grease — and soap has two ends
You only need two ideas. Watch each one wiggle:
Water and grease won't mix
They refuse to hold hands. Drop water on grease and it pulls into little beads and rolls away. The grease stays exactly where it is.
Soap is a two-ended molecule
One end loves water, one end loves grease. The teal head grabs water. The long tail grabs grease. One tiny molecule, two opposite jobs.
2Two ways to rinse
Plain water vs soapy water
Rinsing greasy hands can go two very different ways, depending on what's in the water:
Beads and rolls off
Just water. It can't hold the grease, so it slides right past and leaves the gunk behind.
Surrounds the grease
Water full of two-ended soap. The tails dig in, the heads reach out, and the grease gets wrapped up.
3Your turn — grab a soap molecule
Drag the soap and see which end grabs what
Here's one greasy blob sitting in water. Drag the soap molecule around. Watch the grey tail dive into the grease and the teal head stay out in the water — every single time.
Drag the soap toward the grease blob…
4Now rinse two greasy hands
Same grease, same water — but one hand has soap 🚿
Two equally greasy hands go under the same tap. The only difference: the right hand got a squirt of soap. Guess what happens first — then turn on the water and watch.
Guess before you turn on the tap
Same gunk on both hands, same water. Which hand comes out clean?