A child watches teal goo drip from a spoon while a dimple holds on the same bowl.

Why can goo feel solid and liquid?

It drips… but that dimple holds.

Same bowl. Same goo. Why does it flow one moment and push back the next?

This goo is packed with tiny cornstarch grains. Water winds through the narrow gaps between them.

A magnified bubble above a teal bowl shows crowded tan grains with blue water through their gaps.

A hard push needs a touching grain path that can carry force from one side of the bowl to the other.

Tap to crowd the grains until their contacts connect.

In the usual thick recipe, a slow push gives grains time to slide. A fast push crowds them into contact.

slowfast

Try both speeds in that same normal batch. Only the push time changes.

Choose a push.

New recipe: keep the same scoop of cornstarch, but add one extra cup of water. No punch yet.

The next test keeps the punch just as fast.

Same grains. Same fast punch. One extra cup of water.

Punch this extra-water batch at the same fast speed. What will the fist do?