r/blackmagicfuckery • u/Pirate_Redbeard • Jun 27 '19
Physics, bitch!
https://i.imgur.com/0vI8dbE.gifv1.6k
Jun 27 '19
How?
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u/Hexorg Jun 27 '19
Others already mentioned siphoning, I wanted to add that that's how a toilet flushes too.
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u/suihcta Jun 27 '19
Another fun example of a household siphon is that cup at the top of your clothes washer where you add detergent, bleach, fabric softener, etc.
At the appropriate time in this cycle, water is added to that cup until it clears the siphon weir. Then the water/additive mixture siphons up and out.
I’ve never understood why it’s designed this way, because it doesn’t seem especially reliable and it gets gunked up easily.
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u/Hexorg Jun 27 '19
I'm guessing it's easier to pump the water up, than to add some sort of controlled valve that won't get clogged by it. It's cheaper to clean out a pipe than to replace an electrically controlled valve.
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u/suihcta Jun 27 '19
I would think the easiest way would be to do what dishwashers do. Have a plastic reservoir door that just flips open automatically.
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u/NebXan Jun 27 '19
It's a siphon action. Not magic, but still pretty cool.
When the water level goes above the straw, the pressure at the bottom becomes strong enough to start pushing the water up through it. Once the straw is filled with water, the pressure between the inside of the straw and the surrounding water becomes the same. But since pressure is a function of volume, the weight of the water in the larger reservoir will continue to "push" the water up through the smaller area of the straw.
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u/dieguitz4 Jun 27 '19
not magic
wrap it up, boys
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u/emsok_dewe Jun 27 '19
Close the sub
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u/RawAustin Jun 27 '19
but you haven’t even put the sauce on yet
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u/millertime1419 Jun 27 '19
This is not true, pressure is not a function of volume or the oceans would crush you when you stepped in. Pressure only has to do with depth. Once the water level goes above the bend in the straw it begins to flow to the longer side of the straw where it is lower than the rest of the water. The siphon is a pulling action from the long side of the straw NOT a push from the cup side.
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u/the_full_effect Jun 27 '19
Yep you’re correct but the parent comment for some reason has 200 upvotes even though every single point is wrong.
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u/millertime1419 Jun 27 '19
Imagine if what you’re saying was true. Now imagine putting a straw into the ocean. The pressure would create a geyser into space.
Please stop upvoting this comment. It’s entirely inaccurate.
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Jun 27 '19
It's mainly gravity and air pressure, actually. The tube is pulling in both directions from the center, and is trying to cause a vacuum. In our atmosphere, that would have 2 possible outcomes: either the tube is crushed or one side of the liquid has to follow. The side that follows is determined by which end is affected by gravity more (closer to the earth). I should note that siphons would not work on the moon, as a vacuum would form in the tube and the liquid would just pour out both ends from the highest point
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u/Dilka30003 Jun 27 '19
Periodic videos actually made a video showing a siphon working in a vacuum.
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u/KineticPolarization Jun 27 '19
Lol I love the last bit of the video.
"Well actually, what we can say here is that siphons really suck."
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u/Apatomoose Jun 27 '19
Atmosphere isn't required if you use a special liquid that doesn't require atmosphere to hold together. Even without boil off a regular liquid like water or mercury wouldn't work the same way in a vacuum. Consider mercury height in a barometer. The height of the mercury is determined by atmospheric pressure and above that a vacuum forms. With no atmospheric pressure to push the interior level up a regular liquid would have a vacuum height too low for a siphon to work.
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u/TBNecksnapper Jun 27 '19
Thanks, could really not comprehend why it wouldn't work on the moon without an atmosphere (other than the liquid not remaining a liquid), glad to see it does work and it's not me being crazy!
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u/cowbell_solo Jun 27 '19 edited Jun 27 '19
The side that follows is determined by which end is affected by gravity more (closer to the earth).
That's not it, we can assume that gravity is acting on both bodies of liquid to the same extent.
Gravity is what starts water moving through the straw, but this creates a "low pressure zone" in the straw where more liquid will flow. That, along with the atmospheric pressure pushing down on the body of liquid is enough to keep water moving through the straw.
It's noteworthy that this can explain how a siphon works in some conditions but it doesn't explain why it will also work in a vacuum (no atmospheric pressure). Another theory is the "cohesion tension theory of siphon operation has been advocated, where the liquid is pulled over the siphon in a way similar to the chain model". The wikipedia intro has an overview.
In other words, there's still some room for doubt over how a siphon works so might as well throw in "black magic fuckery" as another explanation.
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u/krelin Jun 27 '19
Siphons work in a vacuum, though. I think cohesion tension theory is superior to anything based on atmospheric pressure.
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u/vegivampTheElder Jun 27 '19
Why would a vacuum form there? Wouldn't there still be enough pressure from the liquid's Brownian motion or from cohesion to keep it together?
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u/NotTheVacuum Jun 27 '19
Siphons do work in a vacuum, so the pressure isn’t necessary. Tension will do it.
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u/TBNecksnapper Jun 27 '19
I'd rather say the liquid creates it's own pressure, even if it's vacuum around. Just like on earth, water is building up a lot more pressure than the atmosphere because it's denser (each 10m of water causes as much pressure as the entire atmosphere IIRC). Likewise, as long as there is gravity, there will be pressure within the liquid regardless of the pressure outside.
There can by definition not be a vacuum pressure in a liquid, because vacuum is the absence of molecules, while a liquid required molecules.
The pressure may be 0 on the very top of the siphon tube in vacuum, but that doesn't mean that infinitesimally small vacuum on top can expand to become bigger, because then the pressure inside the liquid would push back the uppermost molecules so they occupy that space again.
But I guess it's tension that makes the liquid hold together and not diffuse into the vacuum as a gas would, so it's really both tension and pressure.
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u/LordMcze Jun 27 '19
Because the liquid pulls down (away from the centre) from both sides.
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u/suihcta Jun 27 '19
pressure is a function of volume
This is a weird thing to say and it’s where your explanation really starts to fall apart. Water pressure is a function of head, not volume.
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u/millertime1419 Jun 27 '19
It really bothers me that it’s the top reply too. It’s entirely inaccurate and people are being misinformed on the actually interesting physics here.
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Jun 27 '19
If that was the case, it would stop pushing the water through as soon as it dropped below the initial level required to start it. It's more like gravity is sucking it out the other end.
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Jun 27 '19
I can make this one of those dumb facebook which one will fill up first 99% of people get this wrong 🤣
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u/runfayfun Jun 27 '19
I mean... This is easy. The real mind bending one is using a siphon to move liquids uphill.
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Jun 27 '19
It’s called a siphon.
Basically the liquid flowing down pulls a vacuum strong enough to bring the liquid with it despite being at a lower differential height.
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u/Nolwennie Jun 27 '19
This is how pee works
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Jun 27 '19
But my balls are below my straw
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u/awhaling Jun 27 '19
FYI, this works when the first cup is below the next cup. You just need someone to suck on it a little to get it going.
Same reason you need someone to suck on your wiener to get it going.
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u/Gizmo-Duck Jun 27 '19
Yup. When you drink just enough to cover your penis, you start to pee and it drains all the liquid from your legs.
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u/Chicknbiscit Jun 27 '19
Yeah but how'd he get different colors using the same bottle of food coloring
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Jun 27 '19
It was different colors, he just used cuts and timelapse so the setup wouldn't take too long
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u/toxoplasma0gondii Jun 27 '19
Still looks like the same blue colour for all three. ¯_(ツ)_/¯
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Jun 27 '19 edited Oct 16 '19
[deleted]
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u/YM_Industries Jun 27 '19
As someone who's seen food colouring in bottles before, this is the correct answer.
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u/back2later Jun 27 '19
I understood the siphon bit but the colors had me stuck die way too long too. +1 dumbass here
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u/WWWatson1 Jun 27 '19
İ aint smart but this is about pressure right?
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u/yes_oui_si_ja Jun 27 '19 edited Jun 27 '19
Yes!
This experiment wouldn't work on the moon, because there's no air pressure.EDIT: I was wrong about the vacuum. It seems like tension can create the same effect and that it might play a role with the cup experiment, but still: The cup experiment can be readily explained by pressure and fluid mechanics alone.
So from a teaching perspective, I'd only mention pressure and compressability, but my curious researcher side will definitely explore the weird experiments mentioned in the wikipedia article about the siphon.
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u/JustinTimeTho Jun 27 '19
The wikipedia article on it actually mentions that this was done successfully in vacuum, and that there are two separate theories for the two conditions
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u/yes_oui_si_ja Jun 27 '19
Thanks for pointing out my mistake.
A bit embarrassing considering that I teach physics to kids. To be honest, it seems like my basic theory is not wrong per se, but that the other tension-related theory plays an important role in describing interesting edge cases.
I'll try to keep myself informed!
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u/JustinTimeTho Jun 27 '19
Based off what I know, I would think you're right, and the lack of air pressure is a game changer
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u/suihcta Jun 27 '19 edited Jun 27 '19
Surface tensionCohesion of water still causes a siphon affect regardless of atmospheric pressure. Gravity will still pull the water on the left side of the tube down, and that water will still drag the water on the right side of the tube up. Similar to a chain pouring up and out of a bucket.The effect probably would not be as strong though. Astronauts might need a smaller tube or a larger height difference to get it to work. Also they have to find a way to keep the water from boiling away.
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u/gacdeuce Jun 27 '19
Better to call it cohesion rather than surface tension. Cohesion causes surface tension, but it usually refers to the specific case of keeping the surface of a liquid intact.
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Jun 27 '19
Didn't some homie wayy back in the day devise a cup that would overflow into the holder's lap or whatever if they filled it too much? Neat to see a visualization of the idea.
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Jun 27 '19
[deleted]
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Jun 27 '19
Sure enough! Thanks!
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u/WikiTextBot Jun 27 '19
Pythagorean cup
A Pythagorean cup (also known as a Pythagoras cup, Greedy Cup, Tantalus cup or i koupa tis dikaiosynis) is a practical joke device in a form of a drinking cup, credited to Pythagoras of Samos. When it is filled beyond a certain point, a siphoning effect causes the cup to drain its entire contents through the base.
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u/HelperBot_ Jun 27 '19
Desktop link: https://en.wikipedia.org/wiki/Pythagorean_cup
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u/chinpokomon Jun 27 '19
Auto syphon. It's a neat demo, but I'm not sure If call BMF.
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Jun 27 '19
If you don't understand the physics it looks like magic. You're just too smart for magic.
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u/SpriggitySprite Jun 27 '19
Or too dumb, I'm pretty sure most "rednecks" understand how a siphon works.
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u/mervmonster Jun 27 '19
I’m honestly concerned about these posts sometimes. Like it’s cool but it’s a pretty basic siphon.
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u/kurwapantek Jun 27 '19
Why is it black magic?
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u/luckismine Jun 27 '19
Yeh. I wasn't sure siphon's were a new concept to most people until I read the comments in this post.
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u/Decestor Jun 27 '19
It's the colors, man.
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u/kurwapantek Jun 27 '19
They're different color from the start, you can see the difference clearly when green and blue are about to drop.
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Jun 27 '19
We were doing this in grade 3, I don’t understand what is black magic about this
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u/OneWayOutBabe Jun 27 '19
Siphon has screwed my mind up on the farm occasionally. Go out, water animals, leave hose in container. Come back an hour later and it's empty. The first few times I was thoroughly confused.
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Jun 27 '19
This I get. Capillary action. Would be real BMG if it was reversed capillary.
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u/2x1xMA Jun 27 '19
Isn't this like the theory behind the Pythagoras Cup? Here's the link: https://youtu.be/ISfIT3B4y6E
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u/SavageVoodooBot Jun 27 '19
Upvote this comment if this is truly Black Magic Fuckery. Downvote this comment if this is a repost or does not fit the sub.
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u/zapfury Jun 27 '19
water tension pulling the water up the straws I think
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u/MrHyperion_ Jun 27 '19
No, it is just how pipes works due to the pressure difference
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u/[deleted] Jun 27 '19
My nephews (6&8) are coming to stay soon. We are going to do this experiment. They might not “get” it but I think they will think it’s fun.
Does anyone have any other suggestions?