Name: 怪異的表面張力--60個符號 (Weird Surface Tension - Sixty Symbols)
Uploaded: 2021-01-14T10:30:03.000Z
Duration: 7 min 35 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

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We had a paper accepted about 10 days ago, a paper that we've worked on for a couple of years.

And the reason we're happy is because we've done a fantastic Peter work on its being accepted by physical review letters, which is one of the top journals in the field.

This took me a while this morning, Brady.

What I've done here is I've just got a bowl of water on floating There.

Emergent surface tension in vibrated, non cohesive, granular matter.

But it's impressive because you know that a steel paperclip should be denser than water, and so it should think.

But it doesn't sink, and the reason it doesn't think is because it's sitting on the surface tension of the water.

Normally, it's associating with molecules such as water onto water molecules.

Suppose these air water molecules are attracted to each other by long range forces, the water molecules which have this sort of shape.

They bond together in little triangles, electro statically so they're so small that the electrostatic bombing between the molecules is quite strong.

So what we've done is something completely different.

We've taken a box full of grains of bronze, so this not to scale is a grain of bronze al grains of bronze 150 microns in diameter, and we put them in a box 20 centimeters square.

Let me show you the experiment that we actually did.

That means it's gonna get a little bit noisy on.

Then we put it in the cell and shake it up and down this way at a frequency of 60 hertz.

And so these all start thinking about all over the place.

And you would imagine if you're shaking these about by J picking them up and down, they would become randomized, and they do to some, But under some circumstances, all of them want to go to one side and you get a dense phase over here and there's just a few particles over there.

Okay, so we flip it on and we're expecting that it's gonna face separate into a dense and dilute phase.

Very wise, thes two particles when they're moving together, bashed together and come out with a lesser speed.

So if they hit each other smack on a 10 meters a second bam, they come out with a fraction of that speed.

Well, energy is conserved, but the kinetic energy of the coming in and going out is reduced because some of this goes into heating up the particles on some of it goes into sound, so there is energy loss in the collision on about 30% off.

The velocity is lost in these collisions.

If they're smack on, if they're gentle ones from the side, it's not so damaging.

So what happens is if these come together, you get a little cluster forming on.

They bashed together so many times that they almost come to a standstill.

When they made a little cluster, another one comes in and bashes it.

It makes a little cluster because of the inn elasticity.

The energy loss in these collisions there's a a likelihood that they were plastic together and form little clusters.

What we're seeing here is that it's no separating instantaneously But it's undergoing some separation through a pattern which we call spin Auteuil decomposition just the scientific term for the way that these things separate.

That's 1/3 of a second after thing has been turned on its starts off uniform.

But after 0.3 seconds in this frame, you can see little patches off bronze color.

That's the bronze particles on the darker bits of where few bronze particles are.

And it's starting to want a cluster together into these little heaps and evolved into something which you now look at and say all.

There's a bridge of the continuous path I could wander around here, but what's interesting?

We've got a really nice one here, actually.

What's interesting is that we've got this little circular droplet here on the very fact that that circular tells me that there's a surface tension at play here.

This is just Sam shaking up and down in a box.

There's no into molecular forces holding things together.

This is just me shaking marbles in a box, but it's acting like it's got a surface tension.

Nobody knew that there would be surface tension in this.

If you put water in, there's going to be surface tension of the grains because the water will make little bridges and pull them together.

But before, when you start off with dry grains of bronze, which are nice and shiny with no water there, it wasn't obvious at all that they were going to stick together.

If I put a big bale of hay in the middle of a field and 100 cows okay, because they wanted to have it, they kind of gather around.

I have created surface tension within cows have.

Surely because there's a big round blow doesn't mean that has to be surface tension.

It's ironic that you choose that example because you have.

That's exactly what you've done when you have a system where on animal, for example comes in, I'm going to say normally comes in at right angles to all of the other animals.

Then it might slow down slow down Maur than if it comes in time, gently through all of the other animals, because then it can keep going.

It's a glancing blow if you think about billiard balls moving around on the table, Got a pack of them on one, comes in and hits the pack square.

But if one takes a glancing blow, it just bounces.

Often it keeps most of its energy and its that loss of energy at the interface, which is what creates the surface tension.

By the very definition, we're stretching the interface just a little bit.

We've gone ahead and we've measured this surface tension.

I've got a beautiful graph where we can actually see the difference between the forces pulled this way and the forces pulled this way, just like the paper clip we've gotta wait on.

Then we've got some tension, like a trampoline skin supporting that.

This beautiful circular form on the dark blue region there is showing you where the surface tension actually is.

And we're the first people to have actually measure that in a granular system.

Well, the idea that you take something and shake it is pervasive.

I get my bag of muesli every morning and open a new packet and There's always Brazil nuts at the top or raisins and you shake it up and you think it's going to do it on people try and shake it up, or they try and shake it up powders in medicines to try and make it beautiful.

And it doesn't work because for some reason things like to cluster together.

And in this case they seem to cluster together on dhe, separate out into different bits.

So this is something which is not understood it all.

This is one of the big, difficult problems of the age, as it were.

What happens when you have a system which is not an equilibrium is driven from equilibrium.

Energy is dissipated in some way on, yet it seems to reach a steady state, which you can't describe using the normal laws of physics.

 So in here, this is our, uh, economical supercomputer, Shall we call it? 

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怪異的表面張力--60個符號 (Weird Surface Tension - Sixty Symbols)

stretch

associate

bizarre

experiment