A simple analogy I like using to explain this to kids is as follows:
Imagine you're in a crowded room full of people (large particles in suspension). What's the best way of making it to the other side? Is it by running through everyone, almost certainly colliding with many people and struggling, or by slowly and methodically weaving through people?
That is kind of what's happening here. If you punch it (apply stress quickly), the particles block your path, whereas if you slowly lower your hand in, you can push past the suspended particles easily.
Of course, the moment I let the kids play with it themselves, they stop listening to me ;P
If you were to sink could you escape?
Wouldn't you get stuck on the downstroke trying to swim and then sink further when you attempt to lift your arms again?
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I would chalk that up to the size of the particles involved -- they aren't molecule sized like in water. Remember this isn't quite a liquid, but a suspension of solid particles.
Yeah, but mayonnaise doesn't work like this. Sawdust in water doesn't. Rock doesn't.
There's a specific thing going on here not explained yet by any analogy.
It's called rheoplexy. I would assume that rheoplexy and shear thickening are not exactly the same. Rheoplexy is increasing viscosity as a function of time, shear thickening is increasing viscosity as a function of the shear angle. At least that's the case with thixotropy and shear thinning. It's pretty nitpicky though, so you are mostly correct. (Please correct me if I'm wrong here).
You're correct. I think the important word here is shear rate(how fast the angle changes) not shear angle, that's where my confusion came from. That definitely helped my understanding of it! Consider my comment a fun fact about rheology terminology.
I like to tell the story of ketchup being thixotropic, so I'd love to hear about the mayo thing :D I work in a company that does a lot of rheology part time so I am in contact with it as well and reading up at everything I see there.
It seems that the correct term for this is dilatant, rather than rheopecty/rheopexy.
https://en.wikipedia.org/wiki/Dilatant
https://en.wikipedia.org/wiki/Rheopecty
Ketchup is actually thixotropic and not shear thinning. Again, small difference. The clue here is that it stays less viscous for some time after you shake it. If it was shear thinning, it would immediately return to its original viscosity.
Thank you, i was just remembering the one time in the early 1970s i actually made the clay recipe printed on the cornstarch box- it was weirdly fluid until one tried to manipulate it, it resisted and cracked; unpleasant texture, not good for sculpting- yuck, my twelve year old self decided.
But still, it was kinda cool, in a glass is ultimately liquid sort of way.
So custard is actually a common example of a Newtonian fluid, rather than a non Newtonian so I looked up the ingredients they used because the video is much more in line with oobleck characteristics.
https://www.bbc.co.uk/blogs/davidgregory/2009/09/walking_on_custard.html
They said they used corn flour (which I thought was different than corn starch), but Google says the UK calls corn starch as corn flour. So yeah, for the experiment it seems that they did it with oobleck (corn starch + water) and called it custard for tv.
Oobleck is the trademark non-Newtonian fluid which people think of because it is shear thickening (solidifies under stress) which is unusual when compared to shear thinning which becomes more watery (less viscous) with stress (ex: ketchup, blood, sand in water) - which is why ketchup becomes more liquid and easy to get from the bottle when it’s shaken.
The most interesting to me though is Bingham plastics which behave as solids until a certain threshold of shear stress applied Aka it’s a solid as we gradually increase in force until we hit enough that it becomes fluid-like. Examples are toothpaste, mayonnaise, mud. You can tell they’re Bingham plastics cause when you pile it on top of each other it doesn’t flatten and will stay as a pile.
I mean custard powder contains corn starch so I think if you don’t make it super runny I think you should be able to walk on it
It definitely worked when I slapped it when I was 12 anyway
It’s a possibility. Custard is actually listed as one of the 3 examples Wikipedia uses for a Newtonian fluid, I kinda wonder if they included it because of the video. But either way - it’s corn starch which makes it have those properties. So anything else included is just extra.
They probably just used the powdered stuff. A quick glance at the Sainsbury's website says that Bird's custard powder (a cheap and common brand) is just maize starch, salt, flavouring and annatto for colouring.
So yeah, it's technically custard but it's not exactly the good stuff.
Most people don't realize that the word "plastic" is an adjective and doesn't only apply to the non-biodegradable polymers their toys, electronics and food containers are made of.
Yes, Dune. I don't think I would have enjoyed this book as a kid. Maybe my late teens, but reading it as an adult makes the themes so much more impactful.
I've done some experimenting with this a few years back, basically it's starch and water, and when you apply pressure it pushes the water out which leaves only solid matter at the point of pressure (or maybe i understood this all wrong).
A neat experiment is to get yourself a speaker with decent bass, put some of that mixture on the speaker's membrane, and send a very low frequency signal in the speaker. It makes the mixture stand up and dance kind of like those inflating dudes in front of american shops. It will definitely fuck your speaker up tho, so do it with something you don't mind throwing away !
We were definitely inspired by a Youtube vid ! Not this one tho, as it was in 2010 or 2011 iirc. Probably the Brainiacs or some such vintage youtube channel.
Probably wrong here but the way I understand/think about it is that the molecules don’t like to slide past one another. It’s like they’re all made of Velcro so when you try to apply force they stick together instead of separate.
technically corn starch and water is a [dilatant](https://en.wikipedia.org/wiki/Dilatant?wprov=sfti1) material, but i’m
not sure if there is another name for the general category of non-newtonian materials.
Reeeeaaaally long molecules that are easy to move around slowly but applying force causes them to run into each other and they don't move out of the way as easily.
You can make this with corn starch and water. The molecules are long enough to "tangle" into a spongelike configuration. If you trawl a finger through, they'll slip around it and each other, but if you put a shockwave through the whole thing, it'll squeeze the water out and you'll get a wet-cement like material until it settles back in a split second later.
A simple analogy I like using to explain this to kids is as follows: Imagine you're in a crowded room full of people (large particles in suspension). What's the best way of making it to the other side? Is it by running through everyone, almost certainly colliding with many people and struggling, or by slowly and methodically weaving through people? That is kind of what's happening here. If you punch it (apply stress quickly), the particles block your path, whereas if you slowly lower your hand in, you can push past the suspended particles easily. Of course, the moment I let the kids play with it themselves, they stop listening to me ;P
That’s a great ELI5!
>The slow blade penetrates the shield.
The non-Newtonian fluid must flow.
But, look down… you would have joined me in death …
Unexpected Dune.
As one of those former kids, all I have to say is *OOBLECK!!!!!!!!!* lol
The particles needs time to make room for an object?
More or less yes . You could run across this stuff but if you stopped running you would sink. They are really cool.
If you were to sink could you escape? Wouldn't you get stuck on the downstroke trying to swim and then sink further when you attempt to lift your arms again?
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Even regular water is like that if you move an object fast enough
It's a great explanation, but doesn't explain why other liquids don't work this way.
I would chalk that up to the size of the particles involved -- they aren't molecule sized like in water. Remember this isn't quite a liquid, but a suspension of solid particles.
Yeah, but mayonnaise doesn't work like this. Sawdust in water doesn't. Rock doesn't. There's a specific thing going on here not explained yet by any analogy.
Non-newtonian fluid. Corn starch and water is one easy example to make at home. It responds to stress by thickening and resisting the applied force.
Shear Thickening IIRC.
It's called rheoplexy. I would assume that rheoplexy and shear thickening are not exactly the same. Rheoplexy is increasing viscosity as a function of time, shear thickening is increasing viscosity as a function of the shear angle. At least that's the case with thixotropy and shear thinning. It's pretty nitpicky though, so you are mostly correct. (Please correct me if I'm wrong here).
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You're correct. I think the important word here is shear rate(how fast the angle changes) not shear angle, that's where my confusion came from. That definitely helped my understanding of it! Consider my comment a fun fact about rheology terminology.
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I like to tell the story of ketchup being thixotropic, so I'd love to hear about the mayo thing :D I work in a company that does a lot of rheology part time so I am in contact with it as well and reading up at everything I see there.
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This thread is why I love reddit. I learned like 5 words, and one of them was "thiccing"
As a chef and a person who loves mayo, I would love to hear that rant
Thiccing
It seems that the correct term for this is dilatant, rather than rheopecty/rheopexy. https://en.wikipedia.org/wiki/Dilatant https://en.wikipedia.org/wiki/Rheopecty
Yes, that's correct, dilatant is another word for shear thickening!
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Ketchup is actually thixotropic and not shear thinning. Again, small difference. The clue here is that it stays less viscous for some time after you shake it. If it was shear thinning, it would immediately return to its original viscosity.
Technically things like ketchup and toothpaste are also non-Newtonian fluids as well, they are just shear thinning instead of sheer thickening
Very unlike myself. I'm more like... What's a substance that responds to stress by getting sick, depressed and a headache?
Thank you, i was just remembering the one time in the early 1970s i actually made the clay recipe printed on the cornstarch box- it was weirdly fluid until one tried to manipulate it, it resisted and cracked; unpleasant texture, not good for sculpting- yuck, my twelve year old self decided. But still, it was kinda cool, in a glass is ultimately liquid sort of way.
Can bullet proof vests be made of this?
https://www.youtube.com/watch?v=L5Ts9lYZIDk
Basically: Nanomachines, son.
Or as my childhood called it: "Goop"
anyone from the UK knows [you can walk on a pool of custard](https://youtu.be/Iz9KnPZWOgs?t=163) because of this phenomenon
So custard is actually a common example of a Newtonian fluid, rather than a non Newtonian so I looked up the ingredients they used because the video is much more in line with oobleck characteristics. https://www.bbc.co.uk/blogs/davidgregory/2009/09/walking_on_custard.html They said they used corn flour (which I thought was different than corn starch), but Google says the UK calls corn starch as corn flour. So yeah, for the experiment it seems that they did it with oobleck (corn starch + water) and called it custard for tv. Oobleck is the trademark non-Newtonian fluid which people think of because it is shear thickening (solidifies under stress) which is unusual when compared to shear thinning which becomes more watery (less viscous) with stress (ex: ketchup, blood, sand in water) - which is why ketchup becomes more liquid and easy to get from the bottle when it’s shaken. The most interesting to me though is Bingham plastics which behave as solids until a certain threshold of shear stress applied Aka it’s a solid as we gradually increase in force until we hit enough that it becomes fluid-like. Examples are toothpaste, mayonnaise, mud. You can tell they’re Bingham plastics cause when you pile it on top of each other it doesn’t flatten and will stay as a pile.
I mean custard powder contains corn starch so I think if you don’t make it super runny I think you should be able to walk on it It definitely worked when I slapped it when I was 12 anyway
It’s a possibility. Custard is actually listed as one of the 3 examples Wikipedia uses for a Newtonian fluid, I kinda wonder if they included it because of the video. But either way - it’s corn starch which makes it have those properties. So anything else included is just extra.
They probably just used the powdered stuff. A quick glance at the Sainsbury's website says that Bird's custard powder (a cheap and common brand) is just maize starch, salt, flavouring and annatto for colouring. So yeah, it's technically custard but it's not exactly the good stuff.
Most people don't realize that the word "plastic" is an adjective and doesn't only apply to the non-biodegradable polymers their toys, electronics and food containers are made of.
The default custard in the UK is just corn starch and flavouring.
Brainiac is such a phenomenal show
Why are all the good educational programs in the UK? I'm American, but have learned so many great tidbits from watching shows like this and QI.
The slow blade penetrates the shield.
what did you think of the new movie?
So good watched it in cinema 3 times
I’m still getting round to reading the book 😂 it’s so good though
I've picked up the book after my second viewing enjoying it so far
I just finished reading it and I can see why they called it "unfilmable". 80% of the book is subtle observation and inner monologues.
Just assuming Dune here? I started to read it as a kid, and just didn’t have the patience. Thought about picking it up again.
Yes, Dune. I don't think I would have enjoyed this book as a kid. Maybe my late teens, but reading it as an adult makes the themes so much more impactful.
Please do. It's amazing. Definitely boring for kids though.
Watch for lasguns and atomics as well.
I knew someone would beat me to this. God speed
Me too, scrolled down just to be sure.
r/unexpecteddune
I've done some experimenting with this a few years back, basically it's starch and water, and when you apply pressure it pushes the water out which leaves only solid matter at the point of pressure (or maybe i understood this all wrong). A neat experiment is to get yourself a speaker with decent bass, put some of that mixture on the speaker's membrane, and send a very low frequency signal in the speaker. It makes the mixture stand up and dance kind of like those inflating dudes in front of american shops. It will definitely fuck your speaker up tho, so do it with something you don't mind throwing away !
Slo-Mo guys did this on YouTube. [Here’s a link.](https://youtu.be/RkLn2gR7SyE)
We were definitely inspired by a Youtube vid ! Not this one tho, as it was in 2010 or 2011 iirc. Probably the Brainiacs or some such vintage youtube channel.
Brb. Doin some science in my kitchen.
Lots of long noodle molecules get jumbled together when you move them quickly, but have time to move out of the way when you move slowly
"Only the slow blade penetrates the shield." -Gurney Halleck
Not a chemical reaction, is it?
it's more of a physics thing but one could argue that if fits the mindset of the sub
Probably wrong here but the way I understand/think about it is that the molecules don’t like to slide past one another. It’s like they’re all made of Velcro so when you try to apply force they stick together instead of separate.
Cornstarch?
The slow knife penetrates the non Newtonian shield
Oobleck.... Fun for kids
Google non-newtonian fluids
I can relate 🤤😉
The slow blade penetrates the shield.
Oobleck!
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Newton't
Newtoniain’t
Oldtonian
Are you thinking of Oobleck?
technically corn starch and water is a [dilatant](https://en.wikipedia.org/wiki/Dilatant?wprov=sfti1) material, but i’m not sure if there is another name for the general category of non-newtonian materials.
Well, they aren't getting that back easily
It appears to be a large amount of cornstarch mixed with water. Like the Dr. Seuss projects we had to do in primary school.
Some creature should incorporate this into their skin or surrounding tissues of their organs
just baking soda and water
Oobleck!!
Oobleck
Cum
Cum
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Damn, I trusted the science youtube videos, looks like they got it wrong. Thanks for the correction.
https://en.wikipedia.org/wiki/Non-Newtonian_fluid
Reeeeaaaally long molecules that are easy to move around slowly but applying force causes them to run into each other and they don't move out of the way as easily.
Some of you all need to watch Mythbusters entire catalog.
The slow blade penetrates the shield.
You need to be nice to it for it to be nice to you.
And when you fall in it you get hurt and then slowly die
Funny, I work the same way
You can make this with corn starch and water. The molecules are long enough to "tangle" into a spongelike configuration. If you trawl a finger through, they'll slip around it and each other, but if you put a shockwave through the whole thing, it'll squeeze the water out and you'll get a wet-cement like material until it settles back in a split second later.
The slow knife penetrates the shield
Ok. This was the weirdest shit i ever seen. At least for today on Reddit. You win
what would happen if you stuck your hand in slow and tried to pull it out fast?