Water and air molecules

[Jakewhothinks]

I have a question, does air molecules move the same way water molecules do. So I vape and when I exhale I watch how the concentration of the vape cloud moves. I feel like it moves the exact same way the water molecules move if you dyed water and pour it into a clear thing of water.

[Silvestru]

20 minutes ago, Jakewhothinks said:

I have a question, does air molecules move the same way water molecules do. So I vape and when I exhale I watch how the concentration of the vape cloud moves. I feel like it moves the exact same way the water molecules move if you dyed water and pour it into a clear thing of water.

Hello and welcome. Well you are comparing a gas that you exhale in another "gas" with dyed water that you pour in other water. So I would say that from this comparison no. They do not "move" the same.  Let's wait for other members and for sure will give you a more educated opinion.

[Jakewhothinks]

No I’m not saying another gas that is dyed I’m say a cup of dyed water into a tank of water being able to see the molecules interact

[Strange]

1 hour ago, Jakewhothinks said:

I have a question, does air molecules move the same way water molecules do. So I vape and when I exhale I watch how the concentration of the vape cloud moves. I feel like it moves the exact same way the water molecules move if you dyed water and pour it into a clear thing of water.

They are both fluids, so I would say the interactions would be largely the same. There will be differences because of the different densities and speeds of the molecules in each case, but the patterns of mixing you get with, say, smoke and dyed water are similar.

[studiot]

1 hour ago, Jakewhothinks said:

I have a question, does air molecules move the same way water molecules do. So I vape and when I exhale I watch how the concentration of the vape cloud moves. I feel like it moves the exact same way the water molecules move if you dyed water and pour it into a clear thing of water.

Good question Jake and a good start to this forum.  +1

 

Both gases and liquids are fluids, which means that they deform to take the shape of their container - bottle, bucket hole in the ground whatever, so what is the difference?

The basic difference is that gases expand to fill a container, liquids do not, that is their volume does not change when transferred from one container to another.

A more subtle difference is that liquids have a 'free surface' and gases do not.
An example of a  free surface is the surface of the sea or the top part of your beer in a glass.

 

 

5 minutes ago, Strange said:

There will be differences because of the different densities and speeds of the molecules in each cas

Tempting but not actually true.

I agree with the rest.

Edited September 5, 2018 by studiot

[Strange]

7 minutes ago, studiot said:

Tempting but not actually true.

I'm surprised. I have seen a plume of gas from a volcano rising hundreds (possibly thousands) of metres in the air before forming patterns like this (up the other way, of course) on a much larger scale:

 

 

I assumed the difference in scale was due to the difference in density. If not, what does enable the patterns in air to be much larger than those of ink drops in water? Is it just the scale of the phenomenon: massive amounts of fluid mixing on very large scales versus a tiny amount mixing on small scales?

Kind of a fractal effect? That sounds quite plausible now I think of it; the small scale mixing within the gas plume was probably similar to what is going on in the glass...

[studiot]

It is tempting to use the simple kinetic theory, which compares the single component phases of  liquids and gases (and solids) at conditions well away from the phase interface lines on the material phase diagram.

The closer to that line you get the closer the densities and molecular speeds converge, until they are equal on the line.

Magma is neither a single component nor a single phase material so its rheology is correspondingly complex.

There is also the transition from laminar flow to turbulent flow to consider in your example.
A similar, though less spectacular, effect can be observed by simply turning a tap on and observing the water stream at various flow rates.

Edited September 5, 2018 by studiot

[Jakewhothinks]

thanks! If I have anymore interning questions I’ll be back.

[Strange]

3 minutes ago, studiot said:

It is tempting to use the simple kinetic theory, which compares the single component phases of  liquids and gases (and solids) at conditions well away from the phase interface lines on the material phase diagram.

The closer to that line you get the closer the densities and molecular speeds converge, until they are equal on the line.

Magma is neither a single component nor a single phase material so its rheology is correspondingly complex.

There is also the transition from laminar flow to turbulent flow to consider in your example.
A similar, though less spectacular, effect can be observed by simply turning a tap on and observing the water stream at various flow rates.

Well, I don't think I understood any of that so I'll take your word for it.

Are you saying that velocities of molecules in gases and liquids are (approximately) the same (assuming they are at the same temperature)? 

Not sure how either magma or taps are directly relevant. Although, I suppose you would get a very different effect from dropping coloured water into a glass than you would by shooting a high speed jet of it. But then the question would be (to bring it back to the OP) would that be about the same for two liquids and two gases?

[Jakewhothinks]

The molecules don’t go straight unless having enough velocity to push others out the way. What I’m trying to describe is the circular motion each gas and liquid on how it distributes it’s self. When I blow smoke it go in a shape of vortex kinda unless it has more velocity. Water will do the same thing

[Strange]

13 minutes ago, Jakewhothinks said:

When I blow smoke it go in a shape of vortex kinda unless it has more velocity. Water will do the same thing

Exactly. 

My intuition was that doing this with smoke would form a larger vortex than doing the same thing with (coloured) water. It seems I am wrong (which is always good to learn!)

The basic fluid dynamics (turbulent flow, etc) that create the vortex will be the same in all fluids.

Edited September 5, 2018 by Strange

[studiot]

3 minutes ago, Jakewhothinks said:

The molecules don’t go straight unless having enough velocity to push others out the way. What I’m trying to describe is the circular motion each gas and liquid on how it distributes it’s self. When I blow smoke it go in a shape of vortex kinda unless it has more velocity. Water will do the same thing

Strange was correct, you are asking about the differences between the  fluid mechanics of liquids and the fluid mechanics of  gases.

 

To a first approximation the difference is that liquids are incompressible and gases are compressible.