The Surprising Characteristics of Non-Newtonian Fluids

The Surprising Characteristics of Non-Newtonian Fluids

The putty in your kit - and the original Silly Putty - are silicone polymers. The substance was created during World War II, when the war made natural rubber supplies largely unavailable to the Allies. Chemists worked hard to find an artificial rubber substitute, and voila! – silicone polymer putty was born. Of course, it turned out putty wasn’t very useful for making tires, boot soles, and other wartime supplies, so the formula largely fell by the wayside. Years later it was rebranded as Silly Putty, becoming instantly popular and selling millions and millions of putty-filled plastic eggs.


Your magnetic putty is considered a “viscoelastic non-Newtonian fluid”; viscoelastic means it has both elastic (stretchy) and viscous (thickening) properties when it’s deformed by stretching, pulling, or pushing. Viscoelastic things are actually pretty commonly found - they include nylon, human tissue, wood, rubber, clay and lava (okay, maybe lava isn’t super common). What makes this putty unusual is that it’s more highly elastic, and has a lower viscosity, than most other viscoelastic solids.  


But “non-Newtonian”? What’s it got against Isaac Newton? Really, the putty loves him as much as the rest of us, it’s called non-Newtonian because it doesn’t follow Newton’s Laws of Viscosity. In Newtonian fluids, the thickness remains the same no matter how hard you pull or push it (think of water, for example). This putty is specifically a dilatant non-Newtonian fluid, meaning that viscosity increases when shear force is applied. That’s why it does seemingly odd or counterintuitive things, like snapping when yanked suddenly vs. stretching when pulled slowly, or bouncing when it hits something. Ketchup is a Casson plastic non-Newtonian fluid, which is close to the opposite - the more force applied, the less viscous it becomes. That’s why to get it out of the bottle, you apply force by shaking it up and smacking the bottle. That makes the ketchup less viscous, and it flows right onto your hamburger. 


Non-Newtonian fluids are a lot of fun to play with, and it’s easy to make one yourself at home! The stuff is called “oobleck” after the crazy substance in Dr. Seuss’ 1949 book “Bartholomew and the Oobleck.” The recipe is simple:


  • 1 cup of water
  • 2 cups of cornstarch
  • A couple drops of food coloring, if desired


Mix the ingredients together thoroughly (you can do this by hand), then it’s time to play! Smack your hand down on the oobleck and it instantly solidifies; but push it with your finger (or whole hand) and they goes right through, like a liquid. Try dropping a ball on it! If you have enough water, cornstarch, and space, you could even put it in a bathtub and try to walk on it. And to see the incredible result when you blast oobleck with sound waves, check out the new Vsauce3 video Could You Survive A Quiet Place


And of course, what makes this putty extra special is its magnetic properties; even though the iron particles make up only 3.3% of the putty, they have a powerful effect. We’ve provided you with a robust neodymium magnet, but you can boost the fun by adding more! Gather a couple of magnets together, split the putty in two with long tentacles, and have them “race” to each of the magnetic “goals.” See how the putty reacts to the magnet rocks from your zen garden. If you've got a stack of magnets, lay the putty on top - we’ve found that it will shape itself to the magnetic field of the stack.  


It stretches like an amoeba, laughs in the face of Newton’s laws (of viscosity, at least), and it’s a lot of fun. We hope you enjoy hours of experimentation with your magnetic putty!  


P.S. if you’re wondering what’s in it, the putty is about 65% polydimethylsiloxane, 17% crystalline quartz (that’s where the silica comes from), 9% thixatrol ST (castor oil), 3.3% magnetic iron particles, and a few percentages of other chemical compounds, including 1% titanium dioxide!


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