The All-Devouring Blob

I might be a bit late to the party, but I just saw this the other day:

Holy Tokyo-devouring B-movie blob, Batman! That is awesome! You can check out the clip here: http://www.youtube.com/watch?v=LcQ3GWpy22Y

I’m a little curious how they get the magnetic cube sitting there at the start. Maybe using a magnet underneath the table to hold it in place until the devouring begins? Minor details. 

We’ve clearly got some iron-infused Silly Putty having some fun here. I’m a big fan of Silly Putty, even the non-magnetic sort. We use it in our elementary/secondary school science demos for blowing kids’ minds. If you haven’t played with Silly Putty before (you poor soul…you should stop reading and go get some right now), I’ll tell you how.

The question is whether Silly Putty is a solid or liquid.  First you rip it:

Looks pretty solid to me. It also follows the basic definition of a solid: a material that keeps its own shape. But the real common sense clincher? I’ve certainly never been able to rip water. Solid.

Then you sit the putty on the edge of desk and come back a bit later to find this:

Credit same as above.

Liquids: they fill the shape of the container they’re in. And if that container is shaped like “there’s the edge of a table, and there’s the floor and oh geez cat, don’t knock that glass over!“, well, that’s where it flows. Now tell me that doesn’t look like a liquid.

The mind blowing works best with 4th/5th graders I’ve found, who have a strong feeling for solids and liquids, are certain that one cannot be the other, and aren’t yet too-cool-for-school like high schoolers (for them we save liquid nitrogen for the mind blowing).

Silly Putty can be both a liquid and a solid because it’s a cross-linked polymer. Which really just means it’s a bunch of veeeerry long molecules (polymers) that are anchored to each other. If you anchor the molecules just right, you can get some really wild physical properties – like the ability to confuse the heck out of people who thought they knew what liquids and solids were.

On really short time scales (like bouncing or ripping), it looks like a solid since the long molecules don’t have time to untangle themselves from the knotted ball of molecular yarn. At long time scales (like sittin around on the desk), those molecules can untangle a bit and move around and do liquid-y things. We call these sorts of materials viscoelastic – “visco” because they can be like a viscous fluid, and “elastic” because you can bounce them off your brother’s head. They’re very cool materials and very useful (helmet padding, car bumpers, wrestling mats…).

So the all-devouring blob? At long time scales, like the 1.5 hours making up that gif, the putty can flow around the magnetic cube like a liquid and get all of it’s metal-attracting bits as close to the cube as possible.  And it’s next stop after that? Tokyo.

 

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