Bizarre liquid jets explained - the Kaye effect

I'm kind of a person who gets easily distracted by a side quest. For example, if we're making dinner, after a while my wife will say, "What are you doing?" because for the last 10 minutes I've been turning the faucet on and off or something because I've noticed that I can generate laminar flow but only if I turn the faucet on in a very specific sequence of turns. (It's actually quite interesting, I could make a video about it.) But the point is, it happens to me quite a bit and, for example, recently we were packing some groceries and we bought this huge bottle of shampoo.

The bottle cap had broken and the way I took it out of the bag. The shampoo was spilling on the floor, and I noticed that the way it hit the floor was interesting, the behavior was interesting, so I just stood there watching the shampoo drip on the floor, because I feel like if you notice something interesting and you think more research is required, there is no time like the present. Then, two hours later, with some adjustments to the variables, I noticed some very unusual behavior and reproduced it here under what I generously call laboratory conditions. It's interesting, isn't it?

You see these chaotic

jets

of shampoo shooting in all directions, appearing and disappearing. By the way, watching it in slow motion. This is about one fifth of normal speed. Now I know this is called the Kaye

effect

. K-a-y-e. And it is a result of the fact that the shampoo is diluted, which means that it is viscous, it is thick but its viscosity decreases under the shear force. So shear forces like this, if you have two things sliding past each other, the shear force in the case of a

liquid

is like, if you have a body of

liquid

and at the top it travels like this, at the bottom it is traveling like this. this way you have a velocity gradient through the liquid as it changes direction so you have a shear, a shear force like that and when you apply a shear force to this shampoo the viscosity decreases.

So why does this lead to these

jets

appearing? Well, at the base you have this bed of shampoo that is viscous and incoming you have a stream of shampoo that is also viscous, but because the shampoo pools in the tray occasionally, the incoming stream hits the shampoo bed at an angle and when It does it, it slides and that sliding is a shear force, so you have a shear force. So at the boundary between the incoming stream and the bed, the shampoo dilutes, the viscosity decreases, and creates a layer of lubrication, so the stream can continue to slide further than it would otherwise.

But because this stream comes in with a decent amount of force, it actually pushes down and creates a depression in the shampoo layer. So now you have a jet coming in like this, and then it turns and it has a ramp that shoots up. And in fact, that loop becomes more and more extreme until it finally shoots back on itself and kills the incoming jet, so it's chaotic, which is why the jets come and go. So why does shampoo shear thin out in the first place? Well, part of the answer is by design. For example, it's not the soap content that makes shampoo slimy and thinning, it's an additive.

It's a molecule called a viscosity modifier. The flow properties of your shampoo are adjusted by the manufacturer. Viscosity and shear thinning are useful properties in and of themselves, as if you don't want shampoo or shower gel to slip through your fingers or slip off your hands, so viscosity is good. But at the same time, when you rub it on your hair or on your body, you don't want it to be a laborious process, you want it to become less slimy when you rub it, so shear thinning is also useful. But it's also about perception: It turns out that consumers equate thickness, viscosity with luxury, and in fact, manufacturers modify viscosity for different markets.

It turns out that the average shampoo marketed to a male demographic is more viscous than shampoo marketed to a female demographic. For some reason, men prefer thick shampoo, who knew. But also, for the kids who discovered, literally people research these things: children's shampoo and shower gel are diluted with a much higher shear force, so it takes more force for the viscosity to go down. And that makes sense. As if he had children. If I want my shower gel to stay on their hands because kids can't control their limbs, it's really annoying. And you want it to be very stable, since they shake around in the bath or shower.

So it makes sense. So how do these viscosity-modifying molecules work? How do they add viscosity and how do they dilute? Well, they're polymers, which means they're actually long chain molecules, a little like these bead chains here. And normally they're all tangled together, they can't move very easily and that's why they add viscosity, they add thickness. But if you apply a shear force like this, the molecules disperse, blur, and align. When they are aligned this way, they can flow more easily over each other, so the viscosity decreases. They are thinning due to shear. However, part of the explanation is still missing because shampoo and shower gel are not the only thinning liquids.

Ketchup, mayonnaise, custard, paint, hand sanitizer, they all dilute. But I haven't been able to reproduce the Kaye

effect

with any of those. And I think I know why: there is a time component to this slimming effect. So if you apply a shear force to a liquid it becomes less viscous, but when you remove the shear force it doesn't suddenly become completely viscous again, it takes a little while and in the case of shampoo it's quite fast. So to get the shampoo out of the bottle in that nice stream, a shear force is applied, which has a shear force when it comes out of the bottle.

But by the time the stream reaches the bed of shampoo on which it falls, the viscosity has returned. But in the case of hand sanitizer, or ketchup, or all those other liquids, it's not yet viscous when it hits the ground, so you don't see the effect. As a side note, if you want to reproduce this effect at home you need to have good control over the shampoo stream, and I recommend pouring it into a glass, it makes the whole process much easier. I mean, in general, I think life can be improved by pouring things into a beaker.

So the next time you notice something strange, dig a little deeper. You might find something surprising. And share it with me, because I would like to make a video about it. Well, it's time to get it right again. This time the scenario is this: you are on an island, and on this island there are only three types of people: gentlemen, scoundrels, and pranksters. Gentlemen always tell the truth, knaves always lie, and pranksters can do both. And you meet three people: Erin, Faro and Gobi. And Erin says Faro is a joker. And Faro says that Gobi is a joker.

And Gobi says that Erin is a joker, so she's like a little loop. E says that F is a wildcard, F says that G is a wildcard, and G says that E is a wildcard. The puzzle is this: if exactly one of them is a wild card, how many of them are knights? It's interesting, isn't it? As always, I'm not going to give you the answer because it's very satisfying to get it yourself and I wouldn't want to steal it from you. That said, you can verify your solution using the link in the description, but not until you've tried it yourself.

I mean, I can't control it, so there you have it, the solution is in the description. I found this puzzle on a website called shiny.org which sponsors this video and solving puzzles and problems is absolutely the best way to learn. It's also very fun. I like the way Brilliant has laid out the puzzles. And I like the way they selected the sequence, it really helps you on your learning journey. The steps are very well thought out. So if you want to think like a scientist and like a mathematician, why not try it for free? Go to shiny.org/SteveMould.

The link is also in the description. As an added bonus, the first 200 people to click that link will get a 20% discount on the annual premium membership if they decide to upgrade. I hope you enjoyed this video. If you did, don't forget to subscribe and we'll see you next time. Also click the notification bell. That's something new I have to say at the end of the videos, so there you have it. But it's true, you know, you have to do it, you have to click on the notification bell. Bye bye!