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Science Experiments at Home: Liquids

Can a liquid ever be a solid? How dense is the densest liquid? Are liquids ever magnetic? Let’s have a look at a few experiments—and the science behind them—that you can do at home to explore the wild and wacky properties of liquids.

By
Sabrina Stierwalt, PhD
6-minute read
Episode #152

So, the kids are out from school for the summer, and they are already bored. Or maybe you haven’t been a kid in a while, but you’re missing the experiments you used to do in science class. Here are a few experiments that you can do, with items you most likely already have lying around the house, to explore the fluidity, magnetism, and density of different liquids.

Make Your Own Non-Newtonian Fluid: Oobleck!

Usually, telling the difference between a liquid and a solid is easy. Matter in a liquid state can flow freely and change shape but is not easily compressed and instead maintains a relatively constant volume. Solids are more rigid. They maintain a fixed volume and shape and are thus also not easily compressible.

But can a liquid ever be a solid? Well, not exactly, but some liquids blur the lines normally drawn by these definitions.

Most liquids are what we call Newtonian fluids, a characterization that describes, among other things, their viscosity. Viscosity is a measure of how resistant a substance is to change when different stresses are applied. More viscous liquids, like honey, don’t flow as easily and are considered thicker than less viscous liquids like water. For Newtonian fluids, however, viscosity depends on temperature—if you heat that honey up, it will start to flow more easily.

Non-Newtonian fluids have viscosities that also depend on any forces being applied to the liquid. These substances can become very viscous—so viscous they seem almost solid—if more pressure is applied. This may sound pretty bizarre, but you can make one just using cornstarch and water!

Start with a wide bowl for mixing. If you’re doing this experiment with kids, pick a space where you can make a mess and put some newspaper down. Put about ½ cup of cornstarch in the bowl and add in ½ cup of water but only 2 Tablespoons or so at a time. Use gentle, slow movements to stir the two ingredients as you mix them together, until all of the cornstarch is wet.

What you’ve made is unofficially referred to as oobleck, after the Dr Seuss book, Bartholomew and the Oobleck. In the story, magicians make oobleck fall from the sky to serve a king who wants something different from the usual rain. (Reading the book is also a great related activity for small children.) In reality, what you’ve made is a non-Newtonian fluid.

Experiment with how your oobleck reacts to different types of motion, like a quick sharp tap with a spoon versus a slow and gentle poke from your finger. When you tap the oobleck, it shouldn’t splash like a “normal” liquid because the force you’ve applied has increased the viscosity and made the oobleck more solid-like. (If your oobleck flows too easily, try adding a bit more cornstarch.)

Next, gather some of your oobleck into a ball in your hand. If you continue to pack it down and apply pressure, the goo will maintain it’s solid-like structure. Once you stop, however, it will start to ooze more like a liquid.

Adding a few drops of food coloring to your oobleck can make the experiment a bit more fun. To take your experiment to the next level, you can make your oobleck dance with the help of sound vibrations by spreading it out over a tray on top of a subwoofer or other powerful speaker. When you’re done, be sure to dilute your oobleck with lots of water before pouring it down the drain. Don’t eat it!

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About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.