What’s the Matter?

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By Linda | October 2, 2008

Most of the matter you see every day comes in one of three phases (forms) - Solid, Liquid or Gas. There is also a fourth phase of matter called Plasma (a high energy electrically charged mixture of ions and electrons). Although plasma is the most abundant phase of matter in the universe (it’s what stars are made of), we only see it on earth in a few places such as lightning bolts, flames, auroras, and fluorescent lights.

This month’s issue of Kids Discover Magazine (Volume 18, Issue 10) does a fabulous job of explaining what matter is and defining how different types of matter combine to form Mixtures, Solutions, Alloys, Suspensions, Emulsions, and Colloidal Suspensions. This issue contains some great do-at-home experiments that effectively illustrate these concepts. For my money, Kids Discover has been well worth the subscription price. CLICK HERE to see how you can get Kids Discover at a substantial discount.

Try this fun experiment that illustrates what a colloidal suspension is as well as some very unusual properties unique to this particular mixture.

Cornstarch Quicksand (Oobleck)

Materials

One box of cornstarch (16 oz.)
Large mixing bowl
Cookie sheet or large shallow pan
Pitcher of water
Food color (optional)
Spoon

1. Pour approximately 1/4 of the box (about 4 oz.) of cornstarch into the mixing bowl and slowly add about a half a cup of water. Stir. Sometimes it is easier to mix the cornstarch and water with your bare hands.

2. Continue adding cornstarch and water in small amounts until you get a mixture that has the consistency of honey. It may take a little work to get the consistency just right, but you will eventually end up mixing one box of cornstarch with roughly 1 to 2 cups of water. Notice that the mixture gets thicker or more viscous as you add more cornstarch. Add food color if you wish.

Sink your hand into the bowl of “quicksand” and notice its unusual consistency. Compare what it feels like to move your hand around slowly and then very fast. You can’t move your hand around very fast! In fact, the faster you thrash around, the more like a SOLID the gooey stuff becomes. Sink you entire hand into the goo and try to grab the fluid and pull it up.

Try dropping a small plastic toy animal into the cornstarch mixture and then try to get it out.

Pour the mixture onto the cookie sheet or cake pan. Notice its unusual consistency when you are pouring it into the pan. Stir it around with your finger, first slowly and then as fast as you can. Skim you finger across the top of the glop. What do you notice? Sink your entire hand into the ooze and try to grab the fluid and pull it up.

Try to roll the fluid between your palms to make a ball. Try slapping the surface of the mixture as hard as you can with your open palm. Does it splash?

What’s going on?

The cornstarch and water mixture acts like a solid sometimes, and a liquid at other times. Actually, this concoction is an example of a colloidal suspension - a mixture of tiny, but not molecule-sized bits of one substance suspended (floating) in another. Some other examples of colloidal suspensions are Jell-O, mayonnaise and pudding.

When you compress the cornstarch mixture, you are forcing the long starch molecules closer together. The impact of this force traps the water between the starch chains to form a semi-rigid structure. When the pressure is released, the cornstarch flows again.

All fluids have a property known as viscosity - the measurable thickness or resistance to flow in a fluid. Honey and ketchup are liquids that have a high resistance to flow. Water has a low viscosity. Newton said that viscosity is a function of temperature. So, if you heat honey, the viscosity is less than that of cold honey. The cornstarch and water mixture is an example of a non-Newtonian fluid because its viscosity changes when stress or a force is applied.

Even the most solid materials in our world - cement, steel, rocks are, in reality, made more of empty space than substance. How is this possible? To find out CLICK HERE