I was looking for something else and came across this instead. I’ve seen this in person. There is probably a group like this in your neighborhood, check them out!
Just plain cool.
That was a very cool show. I never got to do anything quite that fun (or big) when I was doing physics demos. They did need a woman on the stage who got a speaking role, though they were pretty good about balancing gender in kids they pulled from the audience.
I remember we did this in fifth grade with a 1 gallon gas can (they were tin back then, and not plastic.) Before he started emptying the air, Teach asked us what we thought would happen. Nobody guessed right, and we jumped when the can suddenly collapsed.
Cool, but I can’t decode what he’s saying at the beginning – Why are they squirting it?
dreikin, they’re squirting it to cool it. They’ve just boiled a tiny amount of water in the bottom to evacuate all the air. He’s holding a pressure gauge, so people can watch it drop. He’s basically explaining what’s going on and what to expect. Not that expecting it keeps anyone from jumping.
Thanks Stephanie Z!
I remember doing something like this with soda cans in a basic science high school class. Heated the can up, and then dunked it in water without letting the water in. Did pretty much the same thing.
Interesting that glass can so easily hold a vacuum in our atmosphere without a problem despite it’s brittleness, but (thin) metal can’t.
“balancing gender” ? Oh, yeah–the weird kids get even more queer when we do that…
” Why are they squirting it?” ?
only the devil knows for sure…
They boiled water inside the steel drum to fill it with water vapor and expel the air that had been inside. Then they sealed the drum. As the drum cooled by radiation and convection, the water vapor began condensing, dropping the vapor pressure inside the drum. By spraying with water, they were speeding the cooling, the condensation, and the pressure decay.
The suddenness of the collapse is due to the failure mode of the drum design.
So we have two phase change examples, and possibly some linguistics here (Graclke, are you an engineer?)
Gas vs. water is one. Gas takes up more space than water. A drum full of gas is a cup or two or whatever full of water. Thus, when water as a gas converts to water as a liquid you get a lot of emptinesss.
A glass container can also explode/emplode with pressure but we make the thick enough.. think about the difference in thickness between a can of soda and an equivilant size bottle of soda. Now, imagine making the metal can with the metal as thick as the glass. That would be a mondo-can that would not implode with a vacuum inside it. Scale that up to the 55 gallon drum and it would be difficult to make it implode. Ad a few design changes to make the edges rounded and the whole thing a solid pice and it would be a container that could “hold a vacuum” (though it is literally not holding a vacuum. It is holding everything else out of the vacuum).
So the thickness and design (and Grackle’s reference to failure mode of drum design) is all about engineering…. chosing materials and working with them properly.
The second phase change physics lesson here is metal vs. microcrystaline structure (silica in solid state).
The atoms in the metal are arrenged in relatinship to each other in a way that lets them move but still stay connected. Like the parts of an old wooden chair that is not a rocking chair but that still sways and rocks around because all the joints need regluing. The atoms of the glass are arranged in a way that does not allow for movement. They are either ‘connected’ or not.
In fact, even though the metal drum ‘collapsed suddenly’ really it was a very slow process of metal deformation and eventual breakage or folding in a fw places. It just looked fast to us. But at the atomic level, it was a slow process compared to what would have happened among silica atoms in an equivalent glass container.
CMF, considering that the audience was fairly evenly split by gender (lots of field trips, I think), it was nice not to see that change as kids were pulled onto the stage.
And you say that as though getting weirder were a bad thing.
Just saw an episode of Bill Nye the Science Guy (rented from library for child) in which he pulled this stunt. Quite cool. Makes me want to bring a barrel to the next BBQ.
One of the guys on this stage was originally on the Bill Nye team.
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