Cornstarch and water to be precise. In the proper mix, it becomes a non-newtonian fluid that behaves like a solid when placed under stress, and a liquid otherwise. I’ve seen demonstrations of the stuff on a much smaller scale, but never anything this size. Looks like fun!
Watch it at YouTube or GoogleVideo.
Found at Physics Blog.
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It’s called dilatent behavior. It happens when you have a system of particles of the same or very close to the same size in a fluid system. When you put stress on the system, the particles can’t move past each other because they all bump into each other, so they just lock into position. This is also the reason that ketchup gets stuck in the bottle, oddly enough. The pureed tomatoes exhibit the same behavior. It’s a serious problem in ceramics processing (I have a degree in Ceramic Engineering, somewhat useless) because dilatent fluids lock when you try to pump them, and they destroy pumps and vessels. You have to have a wide range of particle sizes in a fluid system to get it to behave like a liquid ought to. It seems counter-intuitive that you’d need a wide range, but you can move a densely packed liquid (slurry) much easier than a slurry with particles all the same size.
A better way to demonstrate this so you can see it happen is to take a empty soda bottle, fill it with marbles, then turn it upside down to empty it. You get a few out, but you have to do some shaking to get them to move. If you add some small beads and some sand, the try to pour it out, it should be much easier to pour out.
I don’t know if you were expecting all of this, but I figured I’d explain it if you were interested.
Wow – it works great!
THAT is the coolest thing ever! I used to love to play with the stuff in a bowl.