It’s Goo! It’s Solid! It’s Goo! It’s Solid! It’s— both???
My mom always told me never to play with my food, but in this case, I think even she will agree to make an exception. Not only am I going to play with this food, you should too. It’s way too fun to pass on.
This type of matter is called a “Non Newtonian Fluid”. Why? Well, because it is an exception to the rule Newton devised about the flow and viscosity of fluids.
Newton observed that fluids have a ‘tendency’ to resist flow; he called that tendency “viscosity”. If you have a water-pistol, for example, and you want to splash a target, the harder you press the trigger, the faster water come out. Pressure affects viscosity.
Ketchup is another example. It has very strong ‘resistance’ to flow – its viscosity is high. If you just tilt the ketchup bottle onto your fries plate, it takes a while for it to pour out of the bottle – and onto your plate. Honey is the same. You need to apply pressure on the bottle to force it out.
Newton’s theory was that the only way to change a liquid’s viscosity is to change its temperature. Honey, in that example, flows much more readily when it’s hot. I am not sure if Ketchup follows that example, but you’re welcome to try and let me know. I personally hate warm tomatoes; sauce or no.
Non Newtonian fluids, as their name suggest, are the exception of this rule. They, too, change their viscosity in different temperatures, but they also change viscosity when force is applied on them. And there lies the cool part.
Press down on a glop of honey, and your hands fill with honey. Press down on a glop of oobleck (corn starch and water, for example) and it’s solid.
So, when forces are applied to the glop of Non Newtonian liquid, the forces of attraction between the molecules of the liquid increases, and the liquid becomes solid-like. When the forces decrease, the attraction between the molecules decreases as well, and the glop is again fluid.
Materials needed for the Experiment
- A Bowl
- Corn Starch
- Mop – it’s necessity is proportional to the amount of fun you have with the glop.
- Plastic Bag (to dispose of the mixture)
Warning!!! Do not dispose of the fluid down the drain. It’s going to clog up your pipes, and that’s bad. Put it in a plastic bag and throw it with the garbage, instead.
- Fun. I mean.. c’mon now. It really is. And since corn starch can be found in any food store for cheap, and the preparations take less than 5 minutes to make, you simply must try it yourself. Must.
- “Walking on Water” is probably the most famous fun application of Non Newtonian fluids. You can have examples in YouTube, just by looking up “Non Newtonian Fluids”. Or by watching the MythBusters episode about Ninjas. If only to see the blue corn starch fluid.
- Fluid Armor: Yeah, it sounds weird, but technically, if a fluid turns to solid when force is applied to it, then it makes much more sense to ‘wear it’ as an armor. I wouldn’t recommend using corn starch and water to stop a speeding bullet, but there are other fluids out there that can help in the matter. In fact, in many of the Kevlar armor suits today, there is a few extra layers of special Non Newtonian liquids that react strongly when force is applied. That application makes Kevlar suits lighter, because less layers of fabric are required.
- Non Newtonian Fluids: http://www.madsci.org/posts/archives/mar97/856396884.Ph.r.html
- General Chemistry Online FAQ:
- Oobleck: http://en.wikipedia.org/wiki/Oobleck
- Dr Seuss’ “Bartholomew and the Oobleck”: http://en.wikipedia.org/wiki/Bartholomew_and_the_Oobleck
- “How Stuff Works” on Liquid Body Armor: http://science.howstuffworks.com/liquid-body-armor.htm
- “Army scientists, engineers develop liquid body armor”: http://www4.army.mil/ocpa/read.php?story_id_key=5872