Which materials stay bent after you let go?

Have you ever folded a sheet of paper, the kind you draw on? Lift your hands away, and the fold stays. Which materials stay bent after you let go?

A push from your hands can change an object's shape. What happens next depends on what someone made it from, and how much you bend it. Some things keep a bend, while others pull themselves back.

Soft clay is squishy earth people can shape into bowls. You can bend a roll of soft clay into a curve. Your hands press it into that new shape.

When you let go, soft clay stays curved. It does not spring back into a straight roll. A potter can shape a bowl this way.

Foil is a thin sheet of metal, like the shiny sheet people use to cover food. When you press a firm fold into foil, your hands change its shape. The foil can hold that fold when you let go.

Here comes a little guessing moment. Someone presses a firm fold into a piece of foil, then lifts both hands away. Will the foil open flat again, or keep its fold?

The foil keeps its fold. It does not spring flat again when you lift your hands away. Like soft clay, firmly folded foil can keep its new shape after you let go.

Paper can keep a fold too, if you press it firmly. Your hands squeeze the paper tightly along one line. Even when you open the paper again, that fold line stays.

Rubber usually behaves differently. When you gently bend a soft rubber strip and let go, it springs back toward its old shape. The rubber's stretchy insides pull it back instead of keeping the bend.

How much you bend something matters too. A loose curve in paper may relax when you let go, but a firmly pressed fold stays. So being easy to bend does not always mean keeping a bend.

Think of soft clay, firmly folded foil, and firmly folded paper. These can stay bent after you let go, but rubber usually springs back.

Now you know why a little paper fold can stay right where your hands left it.