Experiments

 newspaper
 measuring cups
 1 cup of dry cornstarch
 large bowl or pan
 food coloring (if you want)
 1/2 cup of water
Put newspaper down on your counter or tabletop. Put the cornstarch into the bowl. Add a drop or two of food coloring. (Use whatever colors you like.) Add water slowly, mixing the cornstarch and water with your fingers until all the powder is wet. Keep adding water until the Ooze feels like a liquid when you’re mixing it slowly. Then try tapping on the surface with your finger or a spoon. When Ooze is just right, it won’t splash–it will feel solid. If you Ooze is too powdery, add a little more water. If it’s too wet, add more cornstarch. Play around with your Ooze! Pick up a handful and squeeze it. Stop squeezing and it will drip through your fingers. Rest your fingers on the surface of the Ooze. Let them sink down to the bottom of the bowl. Then try to pull them out fast. What happens? Take a blob and roll it between your hands to make a ball. Then stop rolling. The Ooze will trickle away between your fingers. Put a small plastic toy on the surface. Does it stay there or does it sink? Ketchup, like Ooze, is a non-Newtonian fluid. Physicists say that the best way to get ketchup to flow is to turn the bottle over and be patient. Smacking the bottom of the bottle actually slows the ketchup down!
Why does my Ooze act like that?
Your Ooze is made up of tiny, solid particles of cornstarch suspended in water. Chemists call this type of mixture a colloid. As you found out when you experimented with your Ooze, this colloid behaves strangely. When you bang on it with a spoon or quickly squeeze a handful of Ooze, it freezes in place, acting like a solid. The harder you push, the thicker the Ooze becomes. But when you open your hand and let your Ooze ooze, it drips like a liquid. Try to stir the Ooze quickly with a finger, and it will resist your movement. Stir it slowly, and it will flow around your finger easily. Most liquids don’t act like that. If you stir a cup of water with your finger, the water moves out of the way easily–and it doesn’t matter whether you stir it quickly or slowly. Your finger is applying what a physicist would call a sideways shearing force to the water. In response, the water shears, or moves out of the way. The behavior of Ooze relates to its viscosity, or resistance to flow. Water’s viscosity doesn’t change when you apply a shearing force–but the viscosity of your Ooze does. Back in the 1700s, Isaac Newton identified the properties of an ideal liquid. Water and other liquids that have the properties that Newton identifies are call Newtonian fluids. Your Ooze doesn’t act like Newton’s ideal fluid. It’s a non-Newtonian fluid.

There are many non-Newtonian fluids around. They don’t all behave like your Ooze, but each one is weird in its own way. Ketchup, for example, is a non-Newtonian fluid. (The scientific term for this type of non-Newtonian fluid is thixotropic. That comes from the Greek words thixis, which means “the act of handling” and trope, meaning “change”.) Quicksand is a non-Newtonian fluid that acts more like your Ooze–it gets more viscous when you apply a shearing force. If you ever find yourself sinking in a pool of quicksand (or a vat of cornstarch and water), try swimming toward the shore very slowly. The slower you move, the less the quicksand or cornstarch will resist your movement.

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 Rubbing (isopropyl) alcohol
 Vegetable oil
 A plastic container or glass jar with an interesting shape (long, skinny olive jars and the fancy jars that hold some marmalades, jams, or jellies work well)
 Small beads, sequins, glitter, or other tiny, shiny things
 Food coloring (if you want)
Fill about 1/4 of the jar with rubbing alcohol. Add a drop of food coloring.

Pour vegetable oil into the jar. Leave about 1/2 an inch of air at the top of the jar. Let the globs of oil settle. Is the oil on top of the alcohol or underneath it?
Drop tiny, shiny things into the jar. Use as many as you want. Don’t use anything too heavy-like a marble-that might break the jar when you shake it.

When all the tiny things are in the jar, carefully pour in more oil until the jar is completely full-right up to the rim.

Screw the lid of the jar on very tightly. (If you want, you can tape around the lid to make sure it won’t leak.)
Gently shake the jar. The oil and alcohol will mix and turn a milky color, and the beads and glitter will float and spin.

Let the oil settle again. That will take about 5 or 10 minutes. Now spin the jar instead of shaking it. What happens?
Why doesn’t the oil float on top of the alcohol?
Since oil floats on top of water, you might have thought that oil would float on top of alcohol, too. But the oil sinks to the bottom and the alcohol floats on top of the oil. Even though water and alcohol are both clear liquids, they have different densities. Alcohol floats on top of oil because a drop of alcohol is lighter than a drop of oil the same size.

Why don’t oil and alcohol mix? For that matter, why don’t oil and water mix?
The answers to these questions have to do with the molecules that make up oil, water, and alcohol. Molecules are made up of atoms, and atoms are made up of positively charged protons, negatively charged electrons, and uncharged neutrons. The atoms that make up water molecules and alcohol molecules are arranged so that there is more positive charge in one part of the molecule and more negative charge in another part of the molecule. Molecules like this are called polar molecules. The charged particles in an oil molecule are distributed more or less evenly throughout the molecule. Molecules like this are called nonpolar molecules. Polar molecules like to stick together. That’s because positive charges attract negative charges. So the positive part of a polar molecule attracts the negative part of another polar molecule, and the two molecules tend to stay together. When you try to mix water and oil or alcohol and oil, the polar molecules stick together, keeping the oil molecules from getting between them-and the two don’t mix. When you try to mix water and alcohol, they mix fine, since both are made of polar molecules.

What’s this pretty toy doing in a set of science experiments? It seems more like an art project to me.

When you make a Glitter Globe, you’re experimenting with two liquids that won’t mix with each other–alcohol and oil. Playing with the Glitter Globe gives you a chance to watch how liquids flow. And in the process, you make something that’s pretty.

Some people think that science and art have very little in common. At the Exploratorium, we disagree. Both artists and scientists start their work by noticing something interesting or unusual in the world around them. Both artists and scientists experiment with the things they have noticed. Art and science begin in the same place-with noticing and experimenting.

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