from Exploratorium and Axel-and-Alice
What could be better than making your very own oozing, gooey slime!
2 parts dry cornstarch
1 part water
First cover your work area with newspapers. (You are making gooey slime. Cleaning up is easiest if all you have to do is throw some paper away rather than scrubbing down the table.)
Put the cornstarch into the bowl. Add a few drops of whichever colour you want your slime to be. Slowly add water, mixing the cornstarch and water with your fingers until all the cornstarch feels wet. Keep adding water until the slime becomes a liquid. You have added enough water when you can tap the surface of the slime and it does not splash. If the mixture is too dry, add a bit more water; if too wet, add a little more cornstarch. Remove your finished slime from the bowl and enjoy!
If you have a bit of slime in your hand and just let it sit there, the slime will spread out and ooze between your fingers like a liquid. But if you squeeze your hand around the slime, it becomes like a solid. So which is it?
Slime is actually a colloidal solution. That means that small particles of cornstarch are suspended in the water but not actually in the water like salt is when you make a cup of salt water. Colloids have different properties than solutions. If you bang on the surface of salt water the water splashes. But if you tap the surface of slime, it feels solid. The more pressure you apply to the surface the harder it becomes. Slime is a non-Newtonian liquid, which means that the viscosity, or resistance, of the liquid changes as you apply a stronger force. If you rest your hand on the surface of slime it will sink in, but it you smack it, the surface is solid. Water is a Newtonian liquid and has an unchanging viscosity. This is why you can swim in water, but not in quicksand, which is like slime.