Why might mixtures of cornstarch and water react like solids sometimes and liquids other times?
Cornstarch and water mix together to form a rather interesting mixture. It looks like a white homogeneous mixture like a thick paint. When you handle it quickly and roughly with lots of motion (like rapidly stirring) it will form a near solid that can be picked up and temporarily handled like a solid. When you allow it to "relax" and sit still the apparent solid will slowly ooze back into liquid form and transfer and pour like a liquid. This behaviour is due to the fact that cornstarch is a polymer. In other words it is made up of molecules that are long linear chains of atoms. When agitated these polymer chains interact against each other to give the mixture solid-like properties. When at rest these polymer chains relax against one another and give the mixture liquid-like flow properties. This is a common demonstration activity in chemistry classes.