Why Silly Putty Bounces Instead of Staying Squashed
Silly Putty is made from long polymer molecules—chains built from repeating chemical units. Boron-containing compounds connect some of those chains at scattered points. These temporary connections act like loose links in a net: they hold the material together, but they can shift and rearrange.
That structure gives the putty a choice between two kinds of motion. When you stretch it slowly, the links have time to move and the chains can slide past one another. The blob flows and changes shape. When you pull or strike it suddenly, the links cannot rearrange as quickly. The network resists the change, so the putty behaves more like an elastic solid.
The Speed of the Action Changes the Result
This is a form of viscoelasticity: a material responds partly like a liquid and partly like an elastic solid, depending on how quickly it is deformed. The distinction is easy to feel. Slowly draw out a piece and it elongates; snap it quickly and it may break. Drop a ball-shaped piece and it rebounds because it deforms and springs back before its internal links have time to flow into a new shape.
The bounce is not an endless return of energy. Some of the impact is lost as heat and internal motion, so the putty rebounds less efficiently than a rubber ball. Its behavior comes from the same molecular network that lets it be molded by hand: given time, the links shift; given a sudden hit, they hold the shape together long enough to spring back.
