My niece has a question that I thought I’d share with the STW minds: if you’re under water blowing bubbles from your mouth or nose, why are they all different sizes? My immediate thoughts are changes in lung pressure, size of the exit (your lips moving) and water currents would result in different sized bubbles?

Is it possible to get a stream of uniformly sized/volume bubbles in a lab tank?

Over to you…

I’d expect it to be changes in the flow rate of the gas leaving your body.

Yes. Glasgow Science Centre has a really cool experiment, a vertical cylinder with clear oil in it and a piston to push air in at the bottom. If you push smoothly you get identical equally-spaced bubbles.

The only flaw is you’ll need to borrow a small child if you want to see it because it’s in the kids’ area!

bum bubbles are a different gas 8)

Would the temperature gradient of the water have an effect as well? Water changes density with temperature, which may effect the size of the bubbles.

Might have some effect, but of course they’d also change size with depth – the same bubble will get larger as it rises.

The bubbles will also expand as they rise, although thats only noticeable over several meters.

[Edit]wander off for a cup of tea and the astrophysicist wanders in to steel my thunder 😡

Used to work in a lab that made tiny spheres of latex by passing it through a filter underwater and vibrating it, getting them uniform to a fraction of a thousandth of a mm!

bencooper – how tall is the experiment at the Glasgow Science Centre? Aren’t the bubbles affected by the change in oil pressure as the bubbles rise? i.e get larger as they rise?

It’s about 8ft high I guess – they do seem to get a little larger but it’s hard to tell because of the angles and refraction. What’s fun is using a big bubble to catch smaller bubbles – and interesting the shape the bubbles form.

Stab in the dark from vague school science. Van der Waals attraction between the hydrogen bonds in water causes the bubbles of air to want to constantly change shape to get into a sphere. I guess something to do with lowest energy/entropy. Larger the bubble the more susceptible it is to hitting water movement (water considerably denser) and distorting out of sphere shape. Flow rate from mouth is greater than nose so larger and more changing bubbles.

Large bubbles with no water movement will form regular break ups into smaller sphere like bubbles, a bit like fractals in nature (frost on your windscreen).

PS – I have no real idea and probably a simple thing that has some very complicated actual science behind it and some “character” has spent 3 years and a doctorship over.

The bubbles don’t always form spheres:

[video]https://youtu.be/sn67vDBiL04[/video]

I used to be able to do that ^^^ when I dived a bit more regularly………..mind you not as well as that! 😡

Glasgow Science Centre has a really cool experiment, a vertical cylinder with clear oil in it and a piston to push air in at the bottom.

There’s a similar experiment at MOSI in Manchester, but with three cyclinders with oil, water and glycerol in them so you can compare the effects of viscosity too.

Turbulence.

When you blow bubbles, the gas leaving your mouth is actually swirling and moving chaotically – as in, it follows the laws of physics but it’s so complex that it looks random. Because it’s turbulent there are bits of it at higher and lower pressure, so when the water rushes in it’ll flow into the lower pressure areas first leaving the higher pressure areas as bubbles.

If you push gas through a tube (for example) nice and slowly, then it slides over the walls of the tubes smoothly and does’t become turbulent (known as laminar flow I think) and if you do this, bubbles will plop out of the end regularly spaced and sized (as in bencooper’s example).

If you blow harder through the tube, the friction between the gas and the walls of the tube will become too much and the drag on the edge of the gas will slow it down – so as you’ve got the middle going faster than the edges the flow breaks up into turbulence, which is when you’ll get unevenly spaced bubbles.

This turbulence is why you can only get air through a straw so fast – at first, blowing harder makes it go faster, but after a certain point you just get more turbulence, rather than more air flow.

Drips from a tap exhibit similar behaviour. A slowly dripping tap is regular, but increase the flow up to a point it’ll suddenly become chaotic.

(note some of the above may be slightly wrong)

Turbulence.

…..would be a great name for this …

Sorry. Couldn’t help it. As soon as I saw the word Turbulence I couldn’t shake the image of a turban-wearing ambulance out of my head.
In my defence, it’s Friday 😳

Technically, they’re not bubbles. They’re cavities.

You’re welcome.

I think bubbles that emerge from something other than a human would probably be all the same size. I suspect it is more to do with the uneven nature of the nasal cavities and mouth changing shape as air is blown out. If the air is coming from a consistent orifice at a consistent pressure and flow rate into still water then the bubbles would be exactly the same size.

Is there a treadmill under the water?

Yes. Glasgow Science Centre has a really cool experiment, a vertical cylinder with clear oil in it and a piston to push air in at the bottom. If you push smoothly you get identical equally-spaced bubbles.

It was always a joy to see parents explaining the science to their kids or actually trying to figure it all out. unfortunately, during my time working at the science centre it was more like a creche, with us science communicators shepherding kids about while the parents gossiped whilst watching them vandalise the equipment.

The science centre is possibly one of the most unsustainable buildings about considering what it’s supposed to represent. Titanium clad and expensive fittings. I remember wondering why they;d not taken advantage of sustainable energy by wind, tidal and solar at that rather exposed location, next to the river.
Then, when I realised they don’t even have a rigging for cleaning the massive glass side or the steelwork it was just designed with visuals in mind and a build budget of £x and expected to operate.

I think bubbles that emerge from something other than a human would probably be all the same size

You mean a sub-aqua rabbit or something?

I’d agree that it’s turbulences, i.e. fairly chaotic behaviour, even though under some circumstances the bubbles may look similar in size. Van der Waals forces act on much shorter length scales than what we are looking at in bubble formation.

With it being turbulences, I pass over to Sir Horace Lamb (from Stockport) who said: “I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.” One of the funnier science quotes I came across while studying…

The science centre is possibly one of the most unsustainable buildings about considering what it’s supposed to represent.

A few years ago I did a radio thing when the wind turbine was put up next to it. It was for Radio Scotland’s morning show, and I build a little dynamo-powered stationary bicycle which they got their presenter to pedal to power their outside broadcast thing. It was set up in the Science Centre, and while he was pedalling away, he interviewed me about it – not sure why me and not someone from the Science Centre, but they’d given me a list of specs.

Presenter: “So how much more power does that wind turbine produce than what I’m producing?”

Me: “A lot, about a thousand times as much power.”

Presenter: “Wow! So that must be powering most of the Science Centre – how much of the Science Centre’s power is it providing?”

Me: “Not much, only about one thousandth of what it uses.”

They haven’t asked me back 😀

…..would be a great name for this ..

No Pudding

Presenter: “So how much more power does that wind turbine produce than what I’m producing?”

Me: “A lot, about a thousand times as much power.”

Presenter: “Wow! So that must be powering most of the Science Centre – how much of the Science Centre’s power is it providing?”

Me: “Not much, only about one thousandth of what it uses.”

They haven’t asked me back

haha.

I didn’t know there used to be a turbine there, or was it just for the demo?

I’d always thought it’d be great to have some sort of flooring that generates electricity.

like this:http://www.theguardian.com/technology/2015/jan/11/floor-tile-generates-power-from-footsteps-energy-electricity-startup

would probably power the whole place with all the kids legging it around the place 🙂

Still there, isn’t it? Next to Bell’s Bridge, between the SC and the BBC.

Definitely need to get a generator on the big hamster wheel thing on the top floor.