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He's wrong about why that maze towards the end of the video doesn't empty out the supply tank. It's not surface tension, but rather it is the fact that the path

He's wrong about why that maze towards the end of the video doesn't empty out the supply tank. It's not surface tension, but rather it is the fact that the path goes up and down. The down parts of the path will be filled with air, and the up parts will be filled with water. Water is more dense than air, so the supply must have more pressure than the sum of all the heights of the up parts in order for water to flow. This is why you don't have water pipes in your house go up and down loads of times. It can cause an air lock preventing water from flowing.

quickthrower2 4y ago
I thought so, because the first area of surface tension he pointed out is disconnected from the rest of the water. So that surface tension alone would have to explain it. But there was a lot of water up there! I guess it is the same as the upsidedown glass of water with a sheet of paper underneath trick.
Retric 4y ago
Mostly, but surface tension in aggregate is meaningful. Surface tension is doing two things, first it’s contributing to back pressure several times in the same way it’s just barely keeping water from over topping. Secondly it’s taking up volume in air pockets thus increasing the pressure of those pockets. So, if he added soap to reduce surface tension the tank wouldn’t empty but it would end up lower. My guess is roughly an inch but it’s worth testing.
- mywacaday 4y ago
  What's great about this video and the discussion is that something as familiar as water can have new and non intuitive things to learn about it. Are there any other examples of common things that have non obvious behaviour from every day experience?
  - 123pie123 4y ago
    water has a fair number interesting properties https://www.chemistryworld.com/features/the-weirdness-of-water/4011260.article https://www.chemistryworld.com/features/the-weirdness-of-wat...
  - krisoft 4y ago
    > Are there any other examples of common things that have non obvious behaviour from every day experience? How about the chain fountain (also from Steve Mould): https://www.youtube.com/watch?v=_dQJBBklpQQ https://www.youtube.com/watch?v=_dQJBBklpQQ
  - dr_kiszonka 4y ago
    Sounds like great AskHN material to me, especially if you allow computers-related answers : - )
  - btilly 4y ago
    If you pump air through sand, it turns into a fluid. https://thekidshouldseethis.com/post/royal-institution-fluid-sand-video https://thekidshouldseethis.com/post/royal-institution-fluid... An important example application is in getting grain to flow smoothly out of a grain silo. Some substances are "non-Newtonian fluids" meaning that they are liquid normally but turn solid under pressure. Famously, a mixture of cornstarch and water does this, which kids can have endless fun with: https://www.youtube.com/watch?v=Fnd-2jetT1w https://www.youtube.com/watch?v=Fnd-2jetT1w An example application is bulletproof vests which allow their wearers to move normally but will stop a bullet.
    - Georgelemental 4y ago
      > If you pump air through sand, it turns into a fluid. A recently-published fantasy novel uses "seas" of this as a premise: https://www.amazon.com/Tress-Emerald-Sea-Cosmere-Projects-ebook/dp/B0BPNB19CL/ https://www.amazon.com/Tress-Emerald-Sea-Cosmere-Projects-eb...
  - olejorgenb 4y ago
    ZipString/string shooter: https://www.youtube.com/watch?v=rffAjZPmkuU https://www.youtube.com/watch?v=rffAjZPmkuU (other videos: https://www.youtube.com/watch?v=SOEXXlXi4RA https://www.youtube.com/watch?v=SOEXXlXi4RA / https://www.youtube.com/watch?v=f2krPkJ1pfs https://www.youtube.com/watch?v=f2krPkJ1pfs) Slightly related: https://www.youtube.com/watch?v=BSSecjKRxEE https://www.youtube.com/watch?v=BSSecjKRxEE (slow moving waves in moving rope) Bruce Yeany have many good videos covering various physics phenomena.
btbuildem 4y ago
How does that reconcile with the syphon principle? You'd figure that once the water is flowing out of the end, even if the tank was below some of the water's path, the flow would continue until all the water was gone.
- mnw21cam 4y ago
  Siphons work best once air has been excluded from the path. In fact, they work exactly as the opposite to why this maze isn't draining the whole source tank. In a working siphon, the head of water in the downwards direction is greater than the head of water in the upwards direction, which pulls the water forwards. In this case, because of the air columns in the down direction, there is a greater head of water in the upwards direction than the downwards direction, causing a reverse back-pressure.
  - CrazyStat 4y ago
    Yep. It's easy to test for yourself that a siphon will quickly stop working if you let too much air into it. This is also why you can't make very tall siphons, as if the pressure gets too low at the top the water will boil off, create a gas pocket of water vapor, and stop the siphon.
pjsg 4y ago
Yeah -- I was disappointed that he didn't show an example of a maze which is not solved by water (for a finite amount of head). I most often experience this phenomenon is when I'm putting the garden hoses away for the winter when you want all the water out of them. However, if they tend to curl up, then you can get into the state where the water won't come out of the hose once some air gets in. The only solution is to straighten them out.
- kurthr 4y ago
  I agree. It's weird, because I have to believe he realizes how it works (eg what it can "solve" and what it can't). Just demonstrating a little though experiment would go a long way.
jplona 4y ago
https://youtu.be/zdkp9N3qfkI https://youtu.be/zdkp9N3qfkI is a good overview of air lock.

quickthrower2 4y ago

I thought so, because the first area of surface tension he pointed out is disconnected from the rest of the water. So that surface tension alone would have to explain it. But there was a lot of water up there! I guess it is the same as the upsidedown glass of water with a sheet of paper underneath trick.

Retric 4y ago

Mostly, but surface tension in aggregate is meaningful. Surface tension is doing two things, first it’s contributing to back pressure several times in the same way it’s just barely keeping water from over topping. Secondly it’s taking up volume in air pockets thus increasing the pressure of those pockets. So, if he added soap to reduce surface tension the tank wouldn’t empty but it would end up lower. My guess is roughly an inch but it’s worth testing.

mywacaday 4y ago
What's great about this video and the discussion is that something as familiar as water can have new and non intuitive things to learn about it. Are there any other examples of common things that have non obvious behaviour from every day experience?
- 123pie123 4y ago
  water has a fair number interesting properties https://www.chemistryworld.com/features/the-weirdness-of-water/4011260.article https://www.chemistryworld.com/features/the-weirdness-of-wat...
- krisoft 4y ago
  > Are there any other examples of common things that have non obvious behaviour from every day experience? How about the chain fountain (also from Steve Mould): https://www.youtube.com/watch?v=_dQJBBklpQQ https://www.youtube.com/watch?v=_dQJBBklpQQ
- dr_kiszonka 4y ago
  Sounds like great AskHN material to me, especially if you allow computers-related answers : - )
- btilly 4y ago
  If you pump air through sand, it turns into a fluid. https://thekidshouldseethis.com/post/royal-institution-fluid-sand-video https://thekidshouldseethis.com/post/royal-institution-fluid... An important example application is in getting grain to flow smoothly out of a grain silo. Some substances are "non-Newtonian fluids" meaning that they are liquid normally but turn solid under pressure. Famously, a mixture of cornstarch and water does this, which kids can have endless fun with: https://www.youtube.com/watch?v=Fnd-2jetT1w https://www.youtube.com/watch?v=Fnd-2jetT1w An example application is bulletproof vests which allow their wearers to move normally but will stop a bullet.
  - Georgelemental 4y ago
    > If you pump air through sand, it turns into a fluid. A recently-published fantasy novel uses "seas" of this as a premise: https://www.amazon.com/Tress-Emerald-Sea-Cosmere-Projects-ebook/dp/B0BPNB19CL/ https://www.amazon.com/Tress-Emerald-Sea-Cosmere-Projects-eb...
- olejorgenb 4y ago
  ZipString/string shooter: https://www.youtube.com/watch?v=rffAjZPmkuU https://www.youtube.com/watch?v=rffAjZPmkuU (other videos: https://www.youtube.com/watch?v=SOEXXlXi4RA https://www.youtube.com/watch?v=SOEXXlXi4RA / https://www.youtube.com/watch?v=f2krPkJ1pfs https://www.youtube.com/watch?v=f2krPkJ1pfs) Slightly related: https://www.youtube.com/watch?v=BSSecjKRxEE https://www.youtube.com/watch?v=BSSecjKRxEE (slow moving waves in moving rope) Bruce Yeany have many good videos covering various physics phenomena.

btbuildem 4y ago

How does that reconcile with the syphon principle? You'd figure that once the water is flowing out of the end, even if the tank was below some of the water's path, the flow would continue until all the water was gone.

mnw21cam 4y ago
Siphons work best once air has been excluded from the path. In fact, they work exactly as the opposite to why this maze isn't draining the whole source tank. In a working siphon, the head of water in the downwards direction is greater than the head of water in the upwards direction, which pulls the water forwards. In this case, because of the air columns in the down direction, there is a greater head of water in the upwards direction than the downwards direction, causing a reverse back-pressure.
- CrazyStat 4y ago
  Yep. It's easy to test for yourself that a siphon will quickly stop working if you let too much air into it. This is also why you can't make very tall siphons, as if the pressure gets too low at the top the water will boil off, create a gas pocket of water vapor, and stop the siphon.

pjsg 4y ago

Yeah -- I was disappointed that he didn't show an example of a maze which is not solved by water (for a finite amount of head). I most often experience this phenomenon is when I'm putting the garden hoses away for the winter when you want all the water out of them. However, if they tend to curl up, then you can get into the state where the water won't come out of the hose once some air gets in. The only solution is to straighten them out.

kurthr 4y ago
I agree. It's weird, because I have to believe he realizes how it works (eg what it can "solve" and what it can't). Just demonstrating a little though experiment would go a long way.

jplona 4y ago

https://youtu.be/zdkp9N3qfkI https://youtu.be/zdkp9N3qfkI is a good overview of air lock.