Yeah, that part of the magician’s explanation is definitely incorrect.
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I think they clearly do, and so we’re missing context. As @Aeroplane suggests, maybe they had already been told about the lid/screen.
Note that no kid tried to stick their finger all the way up into the water, which is what I would have done. They all just kind of tapped it and sent bubbles up. Certainly, now knowing this and looking again, the last kid is clearly tapping on something.
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There’s a piece of mesh over the mouth of the jar (which was situated between the jar and the card). And likely a somewhat narrow grid. When the kids poke at it, it lets a little water through, but otherwise surface-tension and atmospheric pressure hold back the deluge. It is indeed not quite the classical “atmospheric pressure holds the card over the mouth of the water-filled vessel” demonstration.
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The true force that is holding the water in place is gravity. The same force that keeps an airplane aloft.
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I must be confused; can somebody explain what the difference is between suction and “standard air pressure” in this context?
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Okay the air in the glass presses the water down at 14psi and pressed up on the lid/screen at 14psi so everything stays put. If there is full cover in the water has nowhere to go. It will spill out without the lid screen because the surface tension is not strong enough over the whole opening of the glass, it will hold with the tiny openings on the screen.
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It’s not entirely wrong either, because the water is forming a barrier air cannot pass through - creating an area of fixed pressure and volume. So unless the air can change its temperature, or there’s somehow a method to increase the amount of air in the jar, there is suction involved.
Static equilibrium can still be a cause of suction, not just drawing a vacuum by removing molecules from a volume.
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I sincerely hope that’s a trolley. There is no such thing as a “true force.” (centripetalists:please ignore that) The water is held up because the sum of all forces, including the gravitational pull exerted by Terra, is net zero so the water doesn’t move. If you hold a jar full of water in any orientation out in,say, the ISS, it won’t dump out either.
And gravity doesn’t hold a plane up. Even if you bluster about Bernoulli stuff, the fact is that downward pressure on air forces the plane to stay aloft. Just try stalling the plane and see how well gravity “holds it up.”
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“Harry Potter and the Mysterious Jar that Holds Water, Even When Upside Down” will probably become real when they run out of all the other ideas.
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Nope, is not.
Not sure what this “downward pressure on air forces the plane to stay aloft” is about.
The fact is, air pressure is keeping the water in the glass when it’s upside down and a card is over the opening.
If you press a plunger against a wall and it stays there, “suction” is not keeping it there, air pressure is, the pressure on the outside of the plunger being higher than on the inside.
Air pressure creates lift under the wing of an airplane as it moves through the air (this motion, the moving forward through the air, is usually created by a fossil fuel, and in a real sense, that “true force”, or at least originating force, is from the sun, but I digress) - lower pressure above the wing, higher pressure below the wing (yes Bernoulli stuff).
And what creates air pressure on the planet?
Gravity.
So maybe you don’t like my term “true force” - ok. But think of it this way. If I’m holding a stick and pushing a raisin with it, it’s more accurate to say I moved the raisin than to say the stick moved the raisin (air is the stick, the raisin is the water/plunger/airplane, gravity is me (the true, or originating force)).
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I’ve update the link in my post to a site that reveals the “trick” and the science of why the gimmick works.
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I can’t find the exact part of the relevant episode, but it’s part of this one:
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Oh here it is… and --yay-- it’s the ep before Disney came along and mucked everything up:
One “nifty home experiment” (trial) is the same upside water holder scenario, and it gets to be a running gag. TL;DR–the 12:39 time mark is the one that doesn’t end up with water all going everywhere. The look on the young scientist’s face in each trial is priceless. She nails her lines at 4:50, but the steps to get the experiment to work are what makes good television/video/teaching.
ETA: typo
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“The mоistening.”
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Fantastic! Thanks for sharing that.
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The writing improves much by the end of the first book. Hella funny. I prefer to Rowling’s.
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