Freespace vs air vs vacuum

[TecHNooB]

What is the difference? Don't jump on air and vacuum without taking care of freespace first

 

[Born2bwire]

Under what circumstances?

Plenty of situations where there isn't any though for the purposes of things like acoustics and breathing the difference between air and vacuum is a pertinent one.

 

[CycloWizard]

Freespace isn't defined in Merriam-Webster, so I'm not sure I know what you mean. If I had to guess, it would simply be space in which no mass existed. Air is a solution of gases. A vacuum is simply space which has sub-atmospheric pressure. I'm not sure what you're getting at.

 

[TecHNooB]

Freespace is when permeability and permittivity are 4*pi e-7 and 8.85e-12. That's all I know

 

[Born2bwire]

Freespace is when permeability and permittivity are 4*pi e-7 and 8.85e-12. That's all I know

Free space and vacuum are the same. Air is essentially the same as vacuum in electromagnetics for all intents and purposes. The main caveat that I can think of is the humidity of the air. The water in the air can be absorptive across various frequencies. Generally though, air is not assumed to have any humidity.

 

[TecHNooB]

Free space and vacuum are the same. Air is essentially the same as vacuum in electromagnetics for all intents and purposes. The main caveat that I can think of is the humidity of the air. The water in the air can be absorptive across various frequencies. Generally though, air is not assumed to have any humidity.

My E&M prof said freespace and vacuum are not the same thing. That's where the trouble lies

 

[CycloWizard]

Ah, now I see. Freespace would be the absence of all mass (i.e. in a volume with a density of exactly zero), whereas "vacuum" only implies a sub-atmospheric density. The "power" of the vacuum is usually given in terms of pressure, which is easily converted to density using the ideal gas equation of state.

 

[Murloc]

What is the difference? Don't jump on air and vacuum without taking care of freespace first

assuming that air contains no water
electromagnetic stuff? no difference
mechanical waves and movements? in freespace there is no external drag, and sound can't propagate (no propagation mean).
in vacuum there's less drag than in normal air.

then there is the pressure.

Free space: nothing
Vacuum: some air, pressure is lower
Air: normal atmospheric pressure

 

[Born2bwire]

My E&M prof said freespace and vacuum are not the same thing. That's where the trouble lies

Who is the prof? Unless they are talking about it in terms of a quantum mechanical sense, freespace and vacuum are the same thing in classical electromagnetics from all that I have seen and can remember.

 

[MJinZ]

Vacuum = Outerspace. Even though this is not a perfect one.

I assume free space is Outer Space, but portions of it that literally have nothing.

 

[Paperdoc]

Ah, your question originates in a comment by your E&M prof that freespace and a vacuum are not the same. Well, in the field of electromagnetic signal propagation, "Free Space" transmission of signals refers to sending the signal through air unimpeded by surrounding electrical elements. Contrast this with signal transmission along a pair of wires, or within a waveguide, or within a fiber optic cable. Is that what he / she was talking about? In that sense, Free Space (filled with air) certainly is not the same as a vacuum, because the air DOES have atoms and molecules that can absorb energy from an applied electromagnetic field passing though it.

 

[Born2bwire]

Ah, your question originates in a comment by your E&M prof that freespace and a vacuum are not the same. Well, in the field of electromagnetic signal propagation, "Free Space" transmission of signals refers to sending the signal through air unimpeded by surrounding electrical elements. Contrast this with signal transmission along a pair of wires, or within a waveguide, or within a fiber optic cable. Is that what he / she was talking about? In that sense, Free Space (filled with air) certainly is not the same as a vacuum, because the air DOES have atoms and molecules that can absorb energy from an applied electromagnetic field passing though it.

That might be the correct context. Free space could be referring to a system that allows for unconfined radiation (as opposed to a waveguide or cavity). I do not think that free space is assumed to be air as we use the phrases "permittivity/permeability of free space/vacuum" interchangeably. Thus implying that free space is permeated by a vacuum.

 

[canis]

My E&M prof said freespace and vacuum are not the same thing.

Very informative. I guess the final exam will be:
True or False
Freespace is the same as vacuum.

Better study hard OP.

 

[TecHNooB]

Very informative. I guess the final exam will be:
True or False
Freespace is the same as vacuum.

Better study hard OP.

I graduated already ()

 

[Paperdoc]

To follow up on Born2bwire's comments, he / she is correct. In the context of electromagnetic wave propagation unconfined, "free space" does NOT actually specify the matter in that space. I could be a true perfect vacuum, a partial vacuum, ground-level air or anything else. In each case the permittivity and permeability (or whatever units you use for the frequency-dependent complex propagation coefficients) must be specified. In that sense, "free space" is not so well defined as a "vacuum" is. However, the term "vacuum" by itself does not necessarily involve absence of electromagnetic wave confinement, so that's another aspect of the difference between the two terms.

 

[Born2bwire]

I graduated already ()

Dammit... I feel old... Oh wait!!! I had you confused with RESMonkey who started at UIUC a couple of years back. Pfew... for a second I thought time had really slipped away from me.