Solids are hard materials, like a block of wood or a rock. They have a fixed shape and are not easy to penetrate. Liquids, on the other hand, take the form of the container they’re in, and you can stir through them with a spoon. But this mixture of cornstarch and water might surprise you.
Measure out 130 grams of cornstarch and put it in a bowl.
Add 100 millilitres of water. Gently stir the mixture with a spoon, until everything is well mixed. If all goes well, you will now have a bowl of porridge.
How does it feel if you stir the porridge slowly? And how does it feel if you stir it quickly? Try to take a handful of the mixture from the bowl. Can you knead it into a ball?
What did you discover
Strange mixture, isn’t it?! When it moves slowly, it’s like a liquid. But when you exert force on it (stirring, pressing, kneading), it feels like a solid. During gentle movements, the water molecules can easily move between the cornstarch particles, and the mixture seems to be a liquid.
But during quick movements or when you knead it, you exert more pressure, pushing all of the water molecules out from between the cornstarch particles in one go. This causes the mixture to behave like a solid.