This week, being Science Week in Australia, Roy decided it would be the perfect time to get into science. He always enjoys science experiments, and loves to show the children he knows some of the things he has learned. The question was, which to show you this week. He has done several experiments with the children, and they were really interested in one in particular - a slime, often known as Oobleck, after a book by Dr Seuss. It is a strange slimey goo, which, when it is at room temperature, acts like both a liquid and a solid. The kids were fascinated and wanted to know how it works. So this week, Roy Creates Oobleck - Strangely Solid Slime.
You Will Need:
- Cornflour (wheat cornflour works fine)
- Cold Water
- Food colouring (Roy mixed blue and yellow to make a really good slime green)
To make your oobleck slime, you will need about 1 and a half to 2 cups of cornflour to 1 cup of water. You can of course make as much or as little as you like!
Method:
- In a cup, add the food colouring you plan you use to your water. This will help mix the colour evenly through the slime
- In a large bowl, combine the cornflour and water.
- Stir slowly until the cornflour and water have combined to make a smooth, slimy liquid. You won't be able to stir it quickly.
How To Use Your Oobleck:
- When you gently and slowly move your fingers or a spoon through the slime, it will act like a liquid, just like normal slime does. When you try to move or stir quickly though, it will react like a solid and you will have trouble. You can punch the slime, put it in a mold and turn it out, lift it up, and it will behave like a solid thing, but then when you leave it alone, it will revert to a liquid.
What Is Happening?
This oobleck slime is a great science experiment to make at home, because it is super sciency - even three super science words! It is not only a non-Newtonian fluid, it is also a polymer and a colloid. Three learning experiences all rolled into one weird slime!
First, lets look at oobleck as a colloid. A colloid is something which is made up of one substance suspended in another. Oobleck is a suspension of cornflour in water. The particles (or pieces) of the substance (cornflour) suspended in the other substance (water) are so small that they don't fall through the other to the bottom. Instead the cornflour gets distributed through the water. This suspension allows the suspension to act very differently to either of its components (cornflour and water) when they are alone.
So, being a colloid, oobleck can behave as a non-Newtonian fluid. When we call oobleck a non-Newtonian fluid, what we mean is that its ability to flow (or ooze as the case may be) changes depending on the stress or pressure it is under. If we leave it alone, it will ooze like a normal slime, but when we apply pressure to it, it acts like a solid. You can roll it, punch it, pull it, stretch it, squeeze it, even walk on it (as long as you keep moving and have made a super huge amount!) If you squeeze it hard enough, it will crack and become brittle, but as soon as you put it back in the rest of the oobleck, or even just leave it alone on your hand, it will go back to a liquid state and ooze. As for why this happens, when you put the oobleck under pressure, it's atoms rearrange themselves, allowing it to gain a 'solid' state. When it is not under stress, the atoms are arranged differently.
Oobleck is also made up of polymers though. Starch, as in the cornflour we used, is a naturally occuring polymer which means that it is made up of long chains of molecules, in the case of starch, long chains of sugar molecules. Any time a polymer is added to a liquid, it will make the liquid harder to move. Usually we don't notice this though, because they still move quickly enough. When cornstarch polymers are suspended in water though, they act strangely. If we press against them or move through them slowly, they have time to move aside, so they behave like a liquid. If we apply pressure to them though, by trying to move quickly, or squeezing, rolling, punching etc, the chains of polymers get tangled up together and won't let us pass, acting like a solid.
