Wednesday, August 19, 2009
I am still fascinated by our Goop experiment that we did the other day. So, I decided to do some research into why Feelie Goop behaves the way it does.
Well it turns out that our "Feelie Goop" is an example of a non-Newtonian fluid...specifically a dilatant.
What is a dilatant? Well, to understand the science behind our "feelie goop" imagine that you are walking through a busy train station full of people walking in the opposite direction. To get across the room, you would have to move slowly and find a path between the people. If you tried to run straight across the room at full speed, you would quickly run into another person stopping you in your tracks. This analogy describes the dilatant effect.
The dilatant effect occurs when closely packed particles (like our cornstarch) are combined with enough liquid to fill the gaps between them. At slower speeds, the liquid acts as a lubricant allowing the substance to flow easily. At higher speeds, the liquid is unable to fill the gaps around the particles which causes a great amount of friction. This causes the increase in viscosity. (The term "viscosity" is used to describe the resistance of a liquid to flow. Water, for example, has a low viscosity and flows easily. Syrup has a higher viscosity and doesn't flow as easily.)
So when we press our fingers slowly into our "feelie goop" it allows the cornstarch to move out of the way. However, when we exert a large amount of pressure into the goop (say striking the goop with a hammer), the solid cornstarch particles are not able to get out of the way and the substance behaves more like a solid.
For more ideas on how to experiment with our non-Newtonian substance, check out this video (Video by OragamiSquared):