Leonardo da Vinci observed Capillary Action making him remark that the paint brush was a gift from the gods. He rightfully observed paint brush has an unnatural, given our understanding at the time, attraction for paint. If you place the brush in a cup of paint, and come back some time later, the brush will have _pulled_ the paint into itself noticeably above the surface of the paint in the cup.
It wasn't until the early 1800s that we had the early versions of the Young-Laplace equation which attempted to quantitatively explain the phenomenon.
The wikipedia entry reminds me that this world is full of magic and wonder, everywhere you look. Something as simple as a paintbrush can reveal something peculiar that takes generations of study by the brightest of human minds to try and explain.
Go outside and turn over a rock, any rock, and there is a lifetime of wonder and mystery under it.
And, just because we can explain it now, doesn't mean Leonardo's paint brush isn't magic. It just means that the magic is real.
There's some neat video of Don Pettit who did the work on the prototype version made out of what looks like plastic sheets and Kapton tape. He's very happy to go on shows and talk about it so there's lots of video of him explaining the principals. This [0] is the original NASA recording of him explaining it.
He is the most "uncomfortable" NASA astronaut I have ever seen. He seems to really not want to be on camera whereas every other one I've ever seen is fine with it.
I'm not sure that might just be how he speaks, he seems to do a fair amount of non-mandatory PR engagements if he really didn't like doing them. I read his mood as more "excited energy" from an unpolished public speaker rather than distinctly unhappy to be performing, he came up from the scientist track rather than the pilot/military track for astronauts which can also explain it somewhat maybe.
Apparently the thinning spout shape sucks up the glob of liquid into it by way of capillary action, with the dual benefit of making the glob stay inside the cup despite it being open, while also making it available for slurping at the edge.
I rarely feel some RIT pride but for some reason, seeing this domain on HN sparks it. If you spent many a winter traversing windy long walks and tunnels in Rochester like I did - hoping you are doing well.
Corners are actually super effective at moving liquid using surface tension (assuming the contact angle is such that the surface is concave). The key is that at the front of the liquid, where it's very thin in the corner, the surface has a small radius of curvature => low pressure. If there's a lot of fluid filling up a corner, the radius of curvature is large => high pressure. So fluid naturally flows into the corner. This is used a lot in space applications, e.g., for propellant management devices [1].
The first analysis of the effect I know of is a paper by Concus and Finn (1969) [2], who realized that fluid can be carried arbitrarily high in a triangular groove, even against gravity, and proposed that trees may use this mechanism to carry water to their highest reaches. (The catch is that the fluid front becomes thinner and thinner as it gets higher. And it starts breaking down when it gets so thin that the continuum limit no longer applies).
If you like math, I'd highly recommend checking out Mark Weislogel's research [3] which deals with the dynamics of viscous flow in triangular grooves.
Shameless plug: chapter 4 of my Ph.D. thesis [4] gives an introduction to the subject.
Fluid flows/sticks more easily along the sharp seam than the rounded corners. So there is always a little bit close to that sharp focus point near your lips. You slurp/sip from that sharp point, drawing more fluid along the seam.
But, for exactly the same reasons, this thing is probably a pain to clean. Sharp corners and cleaning don't mix. That narrow seam will likely become caked in the dried residue of a hundred previous drinks. Even in an earth dishwasher, soap scum would be difficult to rinse out. I suspect these are not used many times.
> But, for exactly the same reasons, this thing is probably a pain to clean.
I dunno, given the size I imagine a regular toothbrush could dislodge anything dried, and small sponge-on-a-stick could get it acceptably dry.
It's also worth asking what it might replace: On the ISS do they clean any drink-pouches, or are they all treated as disposable? I imagine that they become trash, since the next drink (or dehydrated drink-to-be) was probably already shipped in its own flattened pouch.
> That narrow seam will likely become caked in the dried residue of a hundred previous drinks
On the other hand, without gravity there is convection, which means those corners probably don't dry out as quickly. If I'm right about that then rinsing left-over residue out with plain water is easier if you don't wait too long.
How gorgeous! It's hilarious how yonic it appears when looking down upon the brim.
I think it works because the narrowing channel has increasing surface area to volume ratio, as you proceed toward the spout, so the capillary forces pull along a gradient toward the spout, gently tugging the liquid toward it.
The bowl of the cup is lightly pinched around the brim to provide a kind of barrier to prevent the globule of zero-g liquid from just floatin' away! Hahaha :)
They say in the article that capillary action draws the coffee along the narrow edge. This is aided by surface tension, just like how water is drawn into a capillary tube.
> “We take gravity for granted,” Pettit said. “Generally, we are unaware of the weight of our hands, or how easily we pour coffee into a cup. We don’t stop to think, ‘Will the coffee rise up and pour out?’ or ‘Can we pour the coffee?’ We just do it. Gravity handles this for us by applying force to the coffee, pulling downward."
Donald Pettit is tugut mang fo wa Earther. Oye, Beltalowda!
Don Pettit is my favorite astronaut. I loved watching all his ISS videos where he did wacky experiments and nerded-out about capillary flows, static attraction and similar stuff.
He's also a renowned photographer and has taken some of the coolest space pictures from the ISS. He actually refined the guidelines for shooting pictures thru the glass windows of the station.
I hope that they fly him again soon; I can't wait to see what he'll come up with next!
I’d love to read more about inventions astronauts developed as a side-effect of being in space. Ie. Not because it was a scheduled project but because they had a problem and hacked together a utility for the problem.
this sounds like a joke of bad taste but I've seen a video of someone drinking from the cup in zero G and it looked so much like a vagina, even more with the added liquid for some reason, that the video looked like a parody skit
That's very neat, but it seems that if you handle it a bit to harshly the liquid will come out and make a mess, unlike the bag. If you are careful enough I guess that's a more flavorful and natural way to drink tho, I like this kind of stuff <3
IIUC spilling liquid in zero-gravity is extremely dangerous.
When you spill on earth, it falls to the floor.
When you spill in space, it floats around and globs up. Then that glob is attracted to, and sticks to, anything that’s hydrophilic. Which happens to include you. More alarmingly, your face.
If I remember correctly there was a recent incident where an astronaut’s dehumidifier in their suit gave out, and they almost drowned in the water being released from their own body (breath, sweat, etc)
This is a neat engineering achievement, but is it practical? What's the benefit of pouring the liquid out of a bag into this versus drinking out of the bag directly?
By having it open to the air you get a lot more of the aroma of the drink which is a bit part of how we experience taste. Mostly it's just a neat trick to demonstrate zero-/micro-G fluid handling and dynamics packed into a relatable form.
Principals like this are used in fuel/liquid handling in space already to make sure your tanks aren't pure chaos and your pumps don't run dry. A lot of rockets just do ullage burns with different motors to settle their fuel into the bottom of tanks but that's not possible for all fluids if you need to have them moving continuously or can't do burns just to settle them.
What's the benefit of using a coffee mug on earth? We risk spilling hot coffee on ourselves and things that can stain, we allow heat to escape to the air, and there is potential for something to get into and contaminate our coffee. And yet most of us probably have a decent collection of coffee mugs. Ergonomics and aesthetics, while perhaps not the very highest priorities, are nevertheless important.
Do you make it in the mug, or do you pour it into the mug after you make it? Why not pour it into a thermos? And why don't you exclusively drink prepackaged coffee?
> Do you make it in the mug, or do you pour it into the mug after you make it?
The difference is that I make it. On the space station, their beverages are pre-made and pre-packaged. You can see the bags in the linked article.
> Why not pour it into a thermos?
Huh? I generally drink out of a mug, not a thermos, but I've used thermoses as well. Again, this situation is different because I generally make my coffee. It's not pre-made and prepackaged.
> And why don't you exclusively drink prepackaged coffee?
Again, huh? Because the coffee I buy comes as beans. I have to add water, heat it up, etc. I sometimes I drink pre-made coldbrew and I do often drink that out of the package it comes in (the bottle/can).
The beverages are not pre-made. Like most of the food that goes up to the space station it is all dehydrated so that you are launching as little water as possible (and therefore additional mass). Water is recycled on the station as much as they can. So they have two methods for making coffee (that I am aware of):
On a space station this size, I'm not sure it's a feature - especially if it starts being used for a more varied selection of consumable liquids than just coffee.
Speaking of, how do they manage smells up there? Is "ISS smell management" someone's job at NASA?
They have filters in the air cycling that I assume include some sort of carbon filter for smell. However, astronauts have definitely noted that the ISS has "a smell"
Makes me wonder in how far you can actually. Wouldn’t the smell molecules also more or less stay roughly in the same space without convection and gravity playing their part?
They still have airflow on the space station. And since brownian motion does a fine job of spreading smells up against gravity on earth, I would guess that it works ok in space too.
Stupid question: Is the math of the design of cup based on the math of the water? In other words, are the actual curves and angles of things derived from the surface tension properties of water in space?
So, if one wanted to make a capillary cup for custard, it'd be different dimensions? Would love to see a parametric version of this (OpenSCAD?) somehow that can be generated for different liquids ...
It would need to be different for custard or it just may not work properly past a certain viscosity point where the resistance to flow in the matter overcomes the forces pulling it into the corner. Or it might just flow slowly enough it's not functional but still forms the same shapes eventually not sure. Zero-G fluid dynamics are difficult to work with intuitively.
To expand on your point a bit, it depends on the type of fluid. Newtonian fluids [1] (a good approximation for water and many other "normal" fluids) will be pulled into the groove regardless of how viscous they are. E.g., the cup would probably work for treacle (syrup). Custard is non-Newtonian; more specifically, it's probably a Bingham fluid [2], meaning it acts like a solid until enough shear stress is applied, and then it acts like a liquid. The problem here is that even if there's enough shear stress for the custard far from the walls to move, the custard deep in the corner will likely remain a solid. So the corner capillary effect won't work.
That is Italian astronaut Samantha Cristoforetti. She is known for installing the first microgravity espresso machine, and brewing the first cup of espresso in space (which depended on the cup shown in the article). The Star Trek uniform references Captain Janeway's love of coffee and willingness to go to extreme measures to ensure its availability.
Leonardo da Vinci observed Capillary Action making him remark that the paint brush was a gift from the gods. He rightfully observed paint brush has an unnatural, given our understanding at the time, attraction for paint. If you place the brush in a cup of paint, and come back some time later, the brush will have _pulled_ the paint into itself noticeably above the surface of the paint in the cup.
It wasn't until the early 1800s that we had the early versions of the Young-Laplace equation which attempted to quantitatively explain the phenomenon.
Fast forward to 1900, Albert Einstein's first paper was still exploring Leonardo's paint brush: https://web.archive.org/web/20171025203011/http://gallica.bn...
The wikipedia entry reminds me that this world is full of magic and wonder, everywhere you look. Something as simple as a paintbrush can reveal something peculiar that takes generations of study by the brightest of human minds to try and explain.
Go outside and turn over a rock, any rock, and there is a lifetime of wonder and mystery under it.
And, just because we can explain it now, doesn't mean Leonardo's paint brush isn't magic. It just means that the magic is real.