Saturday, August 14, 2010

Fun with Big Science Words...

A while ago the Science Mommy posted this exploration of Ooblek.

The Big Kid Scientists may have fun with this one...

Materials: Corn starch, water, container

Procedure:  Mix about a cup of cornstarch with about 1/4 cup of water

What's Going On...
 Isotropy is the property of a fluid to become firm when agitated.  This is what you're experiencing with the cornstarch and water.  You can also see this while walking on wet sand at the beach.  The sand firms up below your feet when you first touch it, then becomes more fluid as your feet sink into the sand.  If you run over the sand, the sand feels firm.  If you walk slowly, your feet will sink.

Thixotropy  is the opposite of isotropy.  The fluid mixture becomes more firm as is it agitated.  An example of this is when you strike the end of a ketchup bottle to get more ketchup out.  The striking force causes the ketchup to become more "runny" and it flows more easily from the bottle.

Originally found at

2 Science Moms have commented...:

Alison said...

"Thixotropy is the opposite of isotropy. The fluid mixture becomes more firm as is it agitated."

Shouldn't that be less? ;)

I've only just learnt what cornstarch is in Dutch, we could try this out in the week. Do you know of any experiments I can do with my 4,5 year old to demonstrate vacuums? We've done the water bottle with holes, and sucked hard on a soda bottle :)

Dancy51 said...

At the plant I work at we use Mag flow meters to measure the flow of liquids in pipes. Whenever a salesman makes a sales visit to get us to switch to his brand he always says "I'll measure anything". I always ask him if it will measure ketchup and he has to admit it won't. Ketchup has a non-Newtonian flow which means it doesn't flow it just folds inside itself like the liquid filled rubber squishy toys that you can't hold on to. We apply Polymer to sludge to get it to coagulate. Sometimes it works so well that the pipe plugs. Just like the cornstarch the more you press the more it plugs. The old Chinese finger puzzle.