Live data from Hacker News

Can water solve a maze? [video]

youtube.com

111–120 of 133 posts

Re: Can water solve a maze? [video]

#111
post #99

Reminded me: https://en.m.wikipedia.org/wiki/Water_integrator The Water Integrator (Russian: Гидравлический интегратор Gidravlicheskiy integrator) was an early analog computer built in the Soviet Union in 1936 by Vladimir Sergeevich Lukyanov. It functioned by careful manipulation of water through a room full of interconnected pipes and pumps. The water level in various chambers (with precision to fractions of a milli…

When I first started learning EE I conceptualized it with water. Ie voltage / potential is a higher water level vs else where. But this takes it to a whole new level, impressive!

There's a whole Wikipedia page for the water-electricity analogy:

https://en.wikipedia.org/wiki/Hydraulic_analogy

Re: Can water solve a maze? [video]

#112
post #69

Earlier quoted context omitted.

Except that this maze clearly has at least two solutions. Straight through the corridor, or via the loop. And that's assuming you don't wander around the loops n times.

Three solutions if you want to be nitpicky. You can go around the clockwise, and counter-clockwise :)

Infinite solutions. You can take as many loops as you like before continuing to the exit.

Re: Can water solve a maze? [video]

#113

The thing that I found most interesting was actually the little side discussion about all mazes being two pieces. Something that I had never considered, but seems fairly self evident (assuming only one path exists through the maze). Also makes me wonder what a proof would look like.

> Also makes me wonder what a proof would look like. Start with the simplest possible maze (i.e. one square with a start and a finish) which will be in two pieces. Then show that all possible additions will not add further pieces except for when you "cut" into an existing piece to make a separate non-solution route (i.e. a looped route that takes you back to the same point). (Having any loops in the maze would break…

This comment took me straight back to Discrete Math in college, learning about inductive reasoning.

Re: Can water solve a maze? [video]

#114

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. T…

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

Re: Can water solve a maze? [video]

#115
post #42

Earlier quoted context omitted.

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 rou…

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?

If you pump air through sand, it turns into a fluid. 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 An example application is bulletproof vests which allow their wearers to move normally but will stop a bullet.

Re: Can water solve a maze? [video]

#116

The thing that I found most interesting was actually the little side discussion about all mazes being two pieces. Something that I had never considered, but seems fairly self evident (assuming only one path exists through the maze). Also makes me wonder what a proof would look like.

Did you see this by any chance? https://twitter.com/matthen2/status/1642236406465454082?s=46...

Re: Can water solve a maze? [video]

#117
post #38

Earlier quoted context omitted.

You can make a maze with only one path (other than paths that double back on themselves), but has three pieces: https://i.imgur.io/R4j6TH3_d.png I think this is basically a flaw in the intuitive definition (or maybe only my intuitive definition) of "doubling back".

Except that this maze clearly has at least two solutions. Straight through the corridor, or via the loop. And that's assuming you don't wander around the loops n times.

But, to me, that requires doubling back on yourself (going through the little passageway twice). This is what I meant by my definition of going back on yourself being wrong

Re: Can water solve a maze? [video]

#118

Earlier quoted context omitted.

> all mazes being two pieces This is true for mazes with only one path from start to end. Each additional path necessitates a separate piece (path permutations nonwithstanding)

> mazes with only one path from start to end One of my favourite bits of trivia: it is this property (being "unicursal") which leads to a maze being more specifically characterized as a labyrinth.

That's interesting, but it's a weird definition. In the myth of the Minotaur, the labyrinth Theseus is trapped in surely must have branches (or he wouldn't need a ball of thread), so it doesn't fit this definition.

Wikipedia[1] also notes this contradiction:

> Although early Cretan coins occasionally exhibit branching (multicursal) patterns, the single-path (unicursal) seven-course "Classical" design without branching or dead ends became associated with the Labyrinth on coins as early as 430 BC, and similar non-branching patterns became widely used as visual representations of the Labyrinth – even though both logic and literary descriptions make it clear that the Minotaur was trapped in a complex branching maze.

[1] https://en.wikipedia.org/wiki/Labyrinth

Re: Can water solve a maze? [video]

#119

The thing that I found most interesting was actually the little side discussion about all mazes being two pieces. Something that I had never considered, but seems fairly self evident (assuming only one path exists through the maze). Also makes me wonder what a proof would look like.

>Also makes me wonder what a proof would look like.

I think you need to be very careful in how you define a maze, lest you run the risk of rediscovering the difficulties involved with the Jordan Curve Theorem.

Re: Can water solve a maze? [video]

#120
post #42

Earlier quoted context omitted.

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 rou…

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?

ZipString/string shooter: https://www.youtube.com/watch?v=rffAjZPmkuU (other videos: https://www.youtube.com/watch?v=SOEXXlXi4RA / https://www.youtube.com/watch?v=f2krPkJ1pfs)

Slightly related: https://www.youtube.com/watch?v=BSSecjKRxEE (slow moving waves in moving rope)

Bruce Yeany have many good videos covering various physics phenomena.

Post reply on HN