Weird Science:Walking on Water

HONOLULU (HawaiiNewsNow)-This is probably one of the best experiments we have ever done on Weird Science with Dr.V! Not only was it mess but we learned a lot about cornstarch and science.

Dr. V Show: Walking on Water

Things you need:

  • 1 box cornstarch
  • Food coloring
  • Water
  • Bowl

The Experiment:

This concoction has been affectionately named "oobleck." Mix 1 part water with 1.5 to 2 parts cornstarch. You might try starting with one cup of water and one and a half cups of cornstarch, then work in more cornstarch if you want a more 'solid' oobleck. It will take some mixing to get nice homogeneous oobleck and it's best to mix it with your hands so that you can feel the consistency as you're working with it. If you'd like, add a few drops of food coloring to give your oobleck some personality! Now that you have your oobleck, try experimenting with it: punch it, poke it quickly, poke it slowly, roll it between your palms, if you have enough of it, try walking on it! You'll be walking on water.

So that's how it works…

We use the term "viscosity" to describe the resistance of a liquid to flow. Water, which has a low viscosity, flows easily. Honey, at room temperature, has a higher viscosity and flows more slowly than water. But if you warm honey up, its viscosity drops, and it flows more easily. Most fluids behave like water and honey, in that their viscosity depends only on temperature. We call such fluids "Newtonian," since their behavior was first described by Isaac Newton. The oobleck is called "non-Newtonian" since its viscosity also depends on the force applied to the liquid or how fast an object is moving through the liquid.

Here's a simple analogy to describe the way oobleck behaves. Think of a busy sidewalk. The easiest way to get through this crowd of people is to move slowly and weave a path between all the people. If you tried running straight into the crowd of people, you would quickly slam into someone and be stopped in your tracks. This is similar to what happens in the cornstarch mixture. The oobleck acts like a crowd of people. Pressing your finger slowly into the mixture allows the cornstarch to move out of the way, but tapping the mixture quickly doesn't allow the cornstarch particles to slide past each other to make way for your finger.

Other non-Newtonian fluids include ketchup and quicksand. Quicksand is like the cornstarch mixture: if you struggle to escape quicksand, you apply pressure to it and it becomes hard, making it more difficult to escape. The recommended way to escape quicksand is to slowly move toward solid ground; you might also lie down on it, thus distributing your weight over a wider area and reducing the pressure. Ketchup is the opposite: its viscosity decreases under pressure. That's why shaking a bottle of ketchup makes it easier to pour.

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