Tuesday, December 27, 2011

how to make your own giant pool of cornstarch

A few years ago, I wrote a post about Steve Spangler and the giant pool of cornstarch he used on the Ellen DeGeneres Show. Little did I know, Steve wrote up his little stunt!

Now, if you'd like to know how to make your own pool of cornstarch you can run across, you can follow Steve Spangler's instructions. You'll need:
  • a container that is 7 feet long, 3 feet wide and about 1.5 feet deep
  • roughly 2,400 pounds of cornstarch
  • 240 gallons of water
  • a cement mixer truck
A quick search unearths this place which apparently sells 50 pound bags of cornstarch for $50, which will set you back about $2400 for the amount you need. Even this place, which sells 50 pounds for the incredible price of $20 per pound will end up costing you $960. But, really, can you put a price on this kind of entertainment?

How does this demo work?

Cornstarch is simply starch derived from corn. "It is ground from the white endosperm at the heart of a kernel of corn. Cornstarch is used as a thickening agent in cooking, a health-conscious alternative to talc, and the main ingredient in a biodegradable plastic." (source)

When mixed with water, one concocts a fabulous substance affectionately referred to as oobleck, after the Dr. Seuss book. Real oobleck is made up of tiny, solid particles of cornstarch suspended in water.

From an Exploratorium source,
When you bang on it with a spoon or quickly squeeze a handful of Ooze, it freezes in place, acting like a solid. The harder you push, the thicker the Ooze becomes. But when you open your hand and let your Ooze ooze, it drips like a liquid. Try to stir the Ooze quickly with a finger, and it will resist your movement. Stir it slowly, and it will flow around your finger easily.

Your finger is applying what a physicist would call a sideways shearing force to the water. In response, the water shears, or moves out of the way. The behavior of Ooze relates to its viscosity, or resistance to flow. Water's viscosity doesn't change when you apply a shearing force--but the viscosity of your Ooze does.

Back in the 1700s, Isaac Newton identified the properties of an ideal liquid. Water and other liquids that have the properties that Newton identifies are call Newtonian fluids. Your Ooze doesn't act like Newton's ideal fluid. It's a non-Newtonian fluid.
Other non-Newtonian liquids include ketchup and quicksand. Check out the Science Friday video for other cool info and experiments.

What else can I do with cornstarch or oobleck?

You can put oobleck on a speaker and watch it (awesome clip #1 - oobleck starts at :58), awesome clip #2, awesome clip #3) Even The Big Bang Theory found this entertaining:

And apparently, according to the Hodgson company, there are about 1 million other uses for cornstarch.

You can read more about oobleck and quicksand on Steve Spangler's blog.

Wednesday, December 21, 2011

3D printers FTW!

A recent (12.10.11) article in the Economist couldn't come at a more perfect time. It's the start of Christmas break, I have free time to read it, and I have been the proud owner of a 3D printer for exactly one week. From the article:

[At] EUROMOLD, a big manufacturing trade fair held in Frankfurt from November 29th to December 2nd [2011], ... 300 or so exhibitors working in three-dimensional printing (or “additive manufacturing” as they prefer to call it).... Some of their 3D printers were the size of cars; others were desktop models. All worked, though, by building products up layer by layer from powered metal, droplets of plastic or whatever was the appropriate material.

I learned about many manufacturers who are using this process to imitate nature. For example:
  • an artificial hip made by Materialise, a Belgian firm (see cool video featuring them)
  • a load-bearing column constructed from filaments of concrete, imitating the basic design of plant stems, and printed by researchers at the Massachusetts Institute of Technology
  • heat exchangers, whose best design resembles a fish gill (more surface area!), by a British firm called Within Technologies
  • light, geodetic structures imitating a “cytoskeleton” of fibrous proteins that holds a cell in shape. The work is being done at Southampton University in Britain, where researchers have printed an unmanned aircraft from laser-sintered nylon (sintering is a way of making objects by heating powders, important for one of the videos below!) OMG - they PRINTED A PLANE!
That ability to create light, strong structures which have complex internal shapes may well turn out to be additive manufacturing’s killer app. The layering of powders or droplets that are then sintered into solidity, or cured with heat or ultraviolet light, allows spaces to be left inside the product. And if such a space would otherwise collapse, it can be filled with a powder that remains intact during curing and is then washed out or blown away. Even moving parts, like clock mechanisms, have thus been made in one go in a 3D printer.


If you'd like to have your own 3D designs printed, there are companies like i.Materialize and Shapeways that will do it for you. Other folks have printed musical instruments, food, blood vessels (?!) and - in the case of this innovative San Francisco company - stylish prosthetics.

But, I've been much more interested in printing 3D objects myself. Preferably with my students, who are much more fearless with technology than I am.


Back in 2008, I first became intrigued with 3D printers when I saw a RepRap at Maker Faire for the first time. They had me at "self-replicating machine." Apparently, if you built one printer, it could PRINT a second set of parts (minus the electronics, metal, etc) for you to build a second machine. This amazed me. Every year since, I have been back to gawk at their booth.

Years later, a student sent me a link to the video demonstrating one of ZCorp's 3D printers. Incredible! (If you want the very technical details about how this works, you can watch Michael Mock's explanatory video.)

Still, not something inexpensive enough for the classroom, although DIY 3D printers were coming down in price. At the 2011 Maker Faire, some 3D printers were selling for as low as $800. Some students and I got to brainstorming fundraisers, and I started looking for grant money.

In the fall of 2011, I attended the NextGen Science Fair and, not surprisingly, hung around the RepRap booth. There, I met Brook Drumm and learned about his plans to create Printrbot, an affordable 3D printer that "can be assembled and printing in a couple of hours." One of his goals is to get 3D printers into the hands of kids!

Fast forward to December 2011: The first Printrbots are ready (you should definitely read all about his Printrbot Kickstarter Project) and Brook came to our school to set up and train us on our very own 3D printer! What will we print? We will be able to use ready-made designs from Thingiverse, or design our own objects using the free programs Google SketchUp or Tinkercad. (One of my students has his gummy bear design ready!) As long as the design can be exported to a .stl file, and is within the boundaries of the Printrbot, we should be able to print it!

Check our the Printrbot and my middle school kids in the video below. The printer is quite new and we have a lot to learn, but it is tantalizing with its possibilities.


Now, if you are still reading, you probably find 3D printing as fascinating as I do. Here are some other incredible videos:

3D Metal printing

Markus Kayser Solar Sinter


And finally, as with all new technologies, there are new issues to consider. Affordable 3D printing brings up new considerations with copyright. Should be interesting to see how it all pans out.