# Injecting an unflated balloon with vacuum

1. Jan 18, 2009

### pentazoid

Would the balloon inflate , deflate or do nothing if I injected the balloon with nothing but vacuum? Is it even possible to inject vacuum into an unflated balloon?

2. Jan 18, 2009

### mgb_phys

inject vacuum = suck air out.
If it is un-inflated it would do nothing (assuming it is totally un-inflated = flat)

3. Jan 18, 2009

### Staff: Mentor

To me, "inject with a vacuum" is just a meaningless self-contradiction. Can you describe exactly how you would do that?

4. Jan 18, 2009

### pentazoid

But don't you have to create a vacuum environment in a proton accelerator in order to create conditions where there is no material except protons and only protons smashing into each other? Why could you not inject vacuum into the inside of a balloon?

5. Jan 18, 2009

### mgb_phys

A vacuum enviroment (like space) isn't filled with vacuum - it's just empty of air.
injecting with vacuum is meaningless - except as a humorous way of saying 'suck air out'.

If you had a full balloon and connected it to a vacuum the air would be sucked out - actually vacuum doesn't suck as such. The air pressing on the outside of the balloon pushes the air and there is no air on the vacuum side pushing back, so the air moves toward the vacuum.

6. Jan 18, 2009

### Staff: Mentor

As simply as I can put it: you're misusing the word "inject". Vacuums are created (usually) with a vacuum pump. The word "inejct" does not apply.

7. Jan 18, 2009

### LURCH

You could inject vacuum, so long as that vacuum is encased in something. A small rigid capsule with vacuum inside could be "injected" into the balloon. This would have the effect of occupying space, displacing the air that is in the balloon, and making it expand.

8. Jan 18, 2009

### mgb_phys

contract?

9. Jan 18, 2009

### Loren Booda

A process like suction relies on a relative vacuum, i. e., where one volume has less air pressure compared to another. So if I try to suck all of the air from the balloon, I am actually allowing atmospheric air pressure to squeeze whatever balloon air there is into the partial vacuum of my mouth and lungs, which perform work against the atmosphere.

10. Jan 19, 2009

### LURCH

No; I'm saying that, if you put an evacuated container inside a balloon, the container will occupy space, displacing air and causing the balloon to expand.

11. Jan 19, 2009

### L62

A balloon that is initially deflated but still open to atmospheric, still contains air inside its cavity. Sucking that remaining air out would make the deflated balloon further collapse to a certain degree, but because the material of the balloon is not hermetic and is permeable, if you keep running the vacuum pump then the air from the atmosphere on the outside of the balloon will be sucked through the balloon material into the pump so it's as if the balloon is no longer there and you are just running a vacuum pump that is open to atmosphere.

12. Jan 19, 2009

### rcgldr

Experiemental vacuums are created in rigid chambers that compress very little in response to pressure differential inside and outside. The balloon is very flexible and there is only a tiny difference between inside and outside pressure, when the baloon is expanded. You'd need a rigid balloon in order to have the pressure inside less than the pressure outside.

13. Jan 19, 2009

### cesiumfrog

So if we inject the (tied) uninflated balloon with a wireframe, it will inflate with a vacuum?

14. Jan 20, 2009

And could we make a vacuum filled balloon light enough so that it floated?

15. Jan 20, 2009

### mgb_phys

Sorry I thought you meant - and then open the container.
(And then made one of those embarrassing typos I generally manage)

16. Jan 20, 2009

### mgb_phys

In theory, however the material for the envelope would be tricky.
It's an interesting exercise - as you make the balloon larger the lifting capacity (and so the mass of material you can use) goes up as size3 while the area (and so the mass) of the envelope only goes as2. The width that the envelope has to span (and so the mass of any internal webbing) only goes as size1

17. Jan 21, 2009

A quick calculation shows that for a spherical balloon the radius would need to be bigger than about 3 times envelope thickness times envelope density.A major design consideration is that the envelope material and structure must be strong enough to withstand atmospheric pressure and this will make any balloon very big (In principle it would be possible to make a vacuum filled balloon that carried passengers.If anyone builds one please do not invite me for a test flight)

18. Jan 21, 2009

### LURCH

I think it also depends on the type of vacuum. For example, you could probably inject a Dustbuster into and unflated balloon, due to its small size and relatively smooth surface.
But a full-sized Dyson with attachments, or a tank-style shop vac would be very difficult to inject.
:tongue2:

19. Feb 19, 2009

### andy taylor

the balloon in vacuum is actually a very old classroom demo to show the power of vacuum. assuming the ballon is flat and empty and in the belljar witha nominal vacuum applied within the jar the balloon will inflate.

Last edited by a moderator: Feb 19, 2009
20. Feb 19, 2009