inside a container with non-pure helium

mikeph

The problem is people are blanketing two separate things under one definition, then using that definition to infer that the two things have the same characteristics. Gases and liquids act very differently- calling them fluids is only useful if you can remember that.

sophiecentaur

If "people" used the relevant terms then there would be no problem. I have just been pointing out that it is not just being 'posy' to ask for the right terms to be used.

krd

Yes it does refer to fluid. But Archimedes would not have been aware of why it was happening. In the context of what is happening, the fluid characteristic is unimportant - the Archimedes principle will work in a gas or a liquid. Flow is not really something you have to think about - more the unbound nature of the particles in gases and liquids, gives a clearer idea. Flow would muddy the water.

Archimedes was aware that displacement of volume led to buoyancy. But he would have been unaware, that there is a connection with thermodynamics. Fluids and flow, were a real puzzle. Even in early classical thermodynamics, heat was thought of as a fluid.

Fluid behaviour can be deceptive. A flow - a laminar flow - can look so smooth from a distance. But if you get really close you can see it isn't. And it's the same with the chaotic swirls of turbulence - from a certain distance they look smooth - you get in really close and they're not. The really complicated nature of fluids emerges from something much simpler.

sophiecentaur

You are just reinforcing my view that one needs to use the right terms in the right situation. A helium balloon would have been a better example, perhaps, but the thermodynamic aspect is hardly relevant to the density / displacement aspect of one fluid (air) supporting another fluid (hot air). There is no difference in principle between that and a bubble in water (another fluid)

Nessdude14

I agree that in every-day context, fluid usually means liquid, but you're on physics forums, and we're discussing physics. In this context, a gas is a fluid, and any decent physicist won't say otherwise.

ZapperZ

This thread is going off-topic. Please get back to the question posed by the OP.

Zz.

krd

Think about it for a minute.

What is the force, driving a bubble in water upwards in water. It's obvious that the bubble is displacing water. What is the force.

You have to start thinking outside the bubble.

Which brings us in a commodius viscus of recirculation brings us back the helium in the room. At typical room temperature the helium will keep mixing with the other gases.

In sea water, or even in typical dead tap water in a glass, you'll find lots of dissolve oxygen - I bet you would find dissolved helium too.

Another really good example is fizzy drinks. Carbon dioxide is dissolved in sugar water. It will happily sit there - energise the drink by giving it a little tap, bubbles appear.

riverrun, past Eve and Adam's, from swerve of shore to bend of bay.

sophiecentaur

I'm not sure what you want out of this. Is it to show that gases and liquids have nothing in common or to show that they have 'fluiditiy' in common? Both of the above are true.

cjl

As an aerospace engineer, who studied fluid mechanics extensively in graduate school (fluids was the focus of my masters degree), anyone who works with fluids frequently definitely considers a gas a fluid. Gases don't just "have fluid characteristics" - they are fluids. More specifically, they are compressible fluids, though in many cases, the compressibility can be neglected.

As for the original question? If released carefully, the gases may remain separate for a period, but they will eventually mix.