Observations and results
Did the cornstarch solution resemble a sluggish white liquid? Did it become a hard solid when you pressed on it, but turn into a liquid when it was allowed to freely move?
Colloidal solutions can act like both a solid and a liquid. The colloidal solution you made does not behave like a typical solid or a typical liquid. Phases of matter such as liquid, gas, solid and plasma are physical properties of matter. The cornstarch solution is a non-Newtonian fluid, which means it does not behave like a Newtonian fluid. When most liquids experience a sideways shearing force, such as by pushing your finger down against them, they move out of the way. The liquids also have a proportionate response, meaning if you push harder, they move out of the way faster. The liquids' viscosity, or resistance to flow, doesn't change. Water, and most fluids, are Newtonian and behave in this way. Because the cornstarch solution is non-Newtonian, however, you should have seen that it does not behave like this. When you put stress on it, such as by pressing down on it or poking it with the fork, it responded by becoming harder, changing to a solid state. When you did not put stress on it, for example by simply holding it in your hand, it again changed its state, this time becoming a runny liquid.
More to explore
Colloids, from University of California, Davis, ChemWiki
Outrageous Ooze, from Exploratorium
Non-Newtonian Fluid, from Discovery Communications
Particle Sizes, from The Engineering ToolBox
Making Mixtures: How Do Colloids Size Up?, from Science Buddies
This activity brought to you in partnership with Science Buddies