Originally published at: https://boingboing.net/2019/05/06/magical-science-demonstration.html
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I love the kid who calls out “WITCHCRAFT!”
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Let the wetting of kitchens begin!
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Did anyone else see an image of the devil flash on the screen? I did…
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Very cool demonstration, i’m a fan of making scientific concepts tangible since you can see a direct correlation of the principles being discussed to actual real world examples. On the flipside i struggled with Math even though i was fairly average at it, but my problem was that it was more on the theoretical abstract side so seeing how it pertains to the real world is much harder.
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This is not the science demonstration it seems to be. It’s a magic trick: https://www.youtube.com/watch?v=IZg1J3ibZ7E. While the “card holding back the water upside down” is a legitimate and classic demo, after removing the card the water would immediately fall out without a gimmicked jar.
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IDK if she later explained to her students what she actually did, but it seems like bad pedagogy to post a video of a magic trick as if it were a real demonstration.
(This does work, for the reason given, up to the point where you take the note card away; making the water stay in the glass after you remove the card requires trickery)
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Yep. I would hope that she showed the class what she was actually doing, because the gimmick itself is also demonstrating the principle. And to let them believe that a liquid can “defy gravity” (short of a liquid helium demo) is REALLY bad pedagogy.
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It sounds like she’s explaining it at the end. “But, there is a small trick. For those of you who haven’t seen it yet…”
I had science teachers who would do a demonstration that defies your expectation and make us come up with multiple, plausible explanations even if someone guessed the right one immediately.
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I remember once the Poland Springs water cooler at work was leaking, and my boss couldn’t figure it out. I pointed to a hole in the jug above the air pocket, and he said “the water’s not leaking out of that, it’s leaking out of the bottom somewhere. The machine must be broken.”
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How come the kids poking the water from below didn’t notice the lid though? It wasn’t what you linked to.
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It was, and no question about it. Why did the kids not react? Who knows? We don’t have enough information to determine that. What we DO know is that as presented this trick violates the laws of fluid mechanics, and in presentation is identical to the trick in the video I link to. If the mechanism is not precisely the same, it’s at least very similar.
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Yeah, this is a concept even well-educated people struggle to apply (e.g. to how siphons work, or why it doesn’t matter what size container you use to measure inches of rainfall). Which is why it seems unhelpful to make lies part of the explanation.
The way this demo is done is using a circle of screen material over the opening. The “magic” version of it is held in place using transparent tape or glue (so the water pours into the glass easily), but here it’s held in place by a ring, as seen in the video. (example link to photo)
Nobody is lying to these kids, they know the screen is there. That’s why they are reaching under the jar and touching it. They are verifying that the screen is there; they aren’t touching some voo-doo void that is keeping the water in.
The trick with the screen works because of surface tension, which is really more of a chemistry/molecular science concept that the air pressure concept the rest of the trick (with the card) and the rest of the application really illustrates. It makes sense that a science teacher wouldn’t get bogged down the by explanation about polar molecules when they are trying to talk about how the air around us functions as a liquid ocean of its own, that there is buoyancy and pressure within.
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“… infectious curiosity”? Someone better tell the Anti-Vaxxers to keep their kids away.
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No not a lid, a screen as shown by @Aeroplane which allows the surface tension in the small gaps to hold the jar of water and would allow for the poking that let some air in as seen. The clear lid in the magic trick would not allow for that.
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Which is, as I said it would be, very similar to the mechanism in the video I linked to. ETA: apologies if my tone came off as snotty. Definitely didn’t intend it that way.
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Though they are still wrong to say it is held in place by suction, just standard air pressure. 14lb/sq inch is a lot of force we just don’t notice it as we are used to it.
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