1What they're made of, way up close
Two ways to build a stretchy thing
If we shrink down small enough to see the tiny pieces, rubber and clay look completely different. Watch each one wiggle:
Rubber: long coiled chains
Rubber is made of super-long molecule chains, all tangled and coiled like springs. A coiled spring always wants to bounce back to its resting shape.
Clay: loose sliding grains
Clay is made of tiny grains packed loosely together. Grains can slide past each other into a new spot — and there's no spring pulling them back.
2Two kinds of "stretchy"
The springy stuff vs the slidey stuff
"Stretchy" isn't just one thing. There are two opposite kinds, and they end up in totally different places:
The springy-chain stuff
Stretch stores a pull in its coiled chains — so it remembers and snaps home.
The sliding-grain stuff
Stretch just slides its grains to a new spot — so it forgets and stays put.
3Your turn — pull on the tiny pieces
Pick one and stretch it yourself
Choose a material, then drag the slider to pull it. You're zoomed way in, so you can watch what its tiny pieces actually do while you stretch — keep your eye on them.
zoomed in on a rubber band
4Now stretch both — and let go
Same pull, then release. Which one comes home? 🪃
Here's the real test. Both pieces are stretched the exact same amount. The only question is what happens the moment you let go. Guess first — then release them together and watch.
Guess before you let go
A rubber band and a clay snake are stretched the same amount. You let go of both at once. Which one springs back to its old shape?