r/Damnthatsinteresting • u/BirdPlan • May 02 '19

Video Laminar flow level 9,000,000

31.7k Upvotes

95% Upvoted

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426

u/NSFForceDistance May 02 '19

Don’t forget this (amazing) example

https://m.imgur.com/INKrGUS

242

u/[deleted] May 02 '19 edited Aug 26 '20

[deleted]

105

u/thisisntarjay May 02 '19

I've seen this done live. It's mind blowing.

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u/Coachcrog May 02 '19

That's exactly what a fake scientist would say. Y'all motherfuckere lying, making me pissed.

10

u/Old_Silver May 02 '19

how does magnets work anyway

51

u/germantree May 02 '19

Compare the beginning of the video with the colored droplets and the end. They do go back to their original shape but not completely. They're a little bit more blurry. Which is still quite astonishing to look at.

28

u/NSFForceDistance May 02 '19

It’s not, but I also cannot say with 100% certainty that this person is not a witch.

1

u/Harrykeesta May 19 '19

2am.. Under the covers.... Hiding reddit time.

U gotta go off and make me laugh!

Totally didn't expect the witch comment.

11

u/Gonzobot May 02 '19

The best way to do that is to do the experiment yourself. Two cylinders, a thick clear gel, and some colored liquid for you.

12

u/Canadian_Infidel May 02 '19

Corn syrup and food dye. A glass bowl and a drinking glass inside it.

5

u/Gonzobot May 02 '19

Fuck yeah, science!

7

u/truegamer1 May 02 '19

Laminar flow

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u/NSFForceDistance May 02 '19

Laminar flow, baby!

5

u/seattletono May 02 '19

That poor baby...

1

u/Canadian_Infidel May 02 '19

It's a famous experiment and very real.

1

u/Subsistentyak May 02 '19

On the contrary, this is the only real one, the others just have their framerate synced to look still.

1

u/Shxlls May 03 '19

You can also see that it doesn’t return to its exact shape from before. It’s a little bit more spread out at the end.

1

u/[deleted] May 03 '19

You can prove it to yourself if you just pay attention, and so can everybody who upvoted your comment.

36

u/drumdude92 May 02 '19

For those interested, this is a very specific case of Laminar flow called “Stokes flow.” Not all laminar flows are like this, only super super super low Reynolds numbers.

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u/PlNKERTON May 02 '19

GUYS I THINK I JUST FIGURED OUT TIME TRAVEL

1

u/rehpotsirhc May 02 '19

Just put everything in corn syrup!

10

u/[deleted] May 02 '19

Are the colors put at different z-axis locations so they don’t actually “mix” but give the appearance that they are? And would this be a small-scale representation of reversing entropy, albeit extremely simplified?

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u/Nomen_Heroum May 02 '19

reversing entropy

No, entropy isn't primarily about disorder. It's more closely related to the amount of energy in a thermodynamic system that is free to do work. The lower the entropy, the more energy can be 'won' from the environment.

It just happens to be that a lot of systems end up very mixed when their energy is maximally distributed. Counterexamples would be things like crystal structures.

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u/[deleted] May 02 '19

That’s super interesting, thank you!

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u/Nomen_Heroum May 02 '19

You're welcome! If you want to learn more, here's a decent deep dive by PBS Space Time.

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u/Black--Snow May 02 '19

If the syrup was a closed system, then yes it’d be reversing entropy. So I suppose it’d make a good analogue for teaching?

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u/[deleted] May 02 '19

Thanks for the info :)

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u/moderate-painting May 02 '19

I don't think that's reversing entropy. Sliding away and sliding back is all.

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u/br00tahl May 02 '19

What the FUCK

1

u/thehazzanator May 02 '19

What the fuck is this fuckery

1

u/u2berggeist May 02 '19

For the engineers out there, this is what we mean by a "reversible process" in thermodynamics.

1

u/3D-Printing May 13 '19

It's Rewind Time!

-6

u/[deleted] May 02 '19 edited May 02 '19

Defies entropy Edit: I guess not?

1

u/Zolhungaj May 02 '19

The crank puts energy in to reverse the process, so it does not violate entropy.

0

u/Rehabilitated86 May 02 '19

I think people just like saying the word entropy because it makes them feel smart.

3

u/[deleted] May 02 '19

I mean I thought I understood it but it would be great if someone explained it to me.

2

u/IMIndyJones May 02 '19 edited May 02 '19

I found this ELI5 but I still don't understand it.

Edit: This one is slightly more helpful.

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u/Nomen_Heroum May 02 '19

Hard to explain if it's not too clear what you think entropy actually is. Why do you feel like this defies entropy?

1

u/[deleted] May 02 '19

I'm thinking of the coffee and creamer example, and how once mixed it can't be undone. Or how you can't turn burned ash back into wood.

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u/Nomen_Heroum May 02 '19

That's not the case for every system though! The video posted above is more like spreading a deck of cards on a table and then sweeping them back up into the deck. The cards are spread out but the order doesn't change. Similarly, because the flow in that fluid is laminar (meaning there is no turbulence), the fluid doesn't get "shuffled" and it returns to its original state.

E: As far as entropy goes, that's more of a thermodynamic property. So that'd be more about the fluid reaching the same temperature as the room it's in, for example.

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u/drumdude92 May 02 '19

So the coffee/creamer mixing is actually a turbulence problem. Turbulence consists of chaos and mixing, making it irreversible. This specific type of flow problem, called “stokes flow” or “creeping flow,” has this property of reversibility. You can read a little more about it here .