# The Naked Scientists Forum

### Author Topic: Empty Can (Air Pressure = 0)  (Read 13584 times)

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« on: 03/01/2008 10:00:14 »
Hi every one,

I'm new here and I know a little about air pressure, I want to know
is that possible to make a Can inside air pressure=0??!!!
I mean without crushing the Can?
Is there any device or "way" to do that?

regards,

#### another_someone

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #1 on: 03/01/2008 11:57:43 »
Firstly, there is absolutely no way you can make air pressure = 0, but you can make it very, very, low, so it is almost zero.

There are vacuum pumps that will remove the air from within a can, but the problem is that the can is then not strong enough to withstand the difference in air normal pressure on the outside, and the absence of air pressure on the inside, and so the can will collapse under that force.

You can build a stronger can that is capable of withstanding that difference in air pressure.

Alternatively, you can make sure there is no air pressure on the outside of the can as well as no air pressure on the inside of the can (e.g. a can in outer space, with no pressure inside or outside, will not collapse).

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« Reply #2 on: 06/01/2008 12:10:58 »
Hi, is that possible to do this operation regularly, i mean making a can or cylinder inside pressure = air pressure then re-empty the can or cylinder (make it almost 0)???

regards,

#### lyner

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #3 on: 07/01/2008 13:41:13 »
'No pressure' means absolutely no molecules in there.
That is a very hard (impossible) condition to achieve.
You have to get to very low pressures in stages. You first use a 'regular pump' - which can either use a piston or a rotating system. Each stroke takes a proportion of the air out but, once the pressure is low enough, as much air comes back in as the pump pumps out.
Once you have a low enough pressure with a conventional pump, you can use a diffusion pump, which uses a special oil with a high boiling point to capture air/gas molecules and, effectively,  washes them away and they can be removed by the conventional 'backing pump'. But there are still bits floating around in there.
There are a few methods which can be used to get even lower pressures - a 'getter' was used to evacuate vacuum tube devices (like CRTs) which involved electrically heating a piece of reactive metal. This combines with spare atoms and sticks them to the side of the tube - you can see a silvery area inside some radio valves, which is all that's left of the getter.
BUT. basically, you will always find the occasional molecule drifting around so you haven't ever got a perfect vacuum. The dirt in the system tends to vaporise, so you have to use very clean equipment or you just 'poison' the vacuum engine.
In deep space, the vacuum is pretty good but there is still about one atom in each metre cube.

#### another_someone

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #4 on: 08/01/2008 04:15:10 »
Apart from air, the very metal of the container itself will have a very slight vapour pressure (e.g. if you have a steel container, there will be a few atoms of iron, etc. floating around in the near vacuum).

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« Reply #5 on: 10/01/2008 10:39:45 »
ok, what i want is a system that makes a pressure near zero, this system should not need more that 12 or 24 volt (or something like that), I'd like to insert an image here but i don't know how.
let's say we have a small ball in a cylinder (fitted to cylinder's diameter), i want this difference in pressure make this small ball move inside the cylinder.

#### lyner

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #6 on: 10/01/2008 15:02:23 »
Would a cheap car 'vacuum cleaner' do the trick?
Details of the actual force needed and the diameter of the cylinder might help, here.
« Last Edit: 10/01/2008 15:04:17 by sophiecentaur »

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« Reply #7 on: 24/01/2008 13:50:58 »
i don't think that car vacuum is depend on pressure, its just a fan, please correct me if I'm wrong.
what i need is a system with 12v or 24v making a mechanical move that changes pressure level in the cylinder (tube) so the ball moves to the lowest pressure side.

#### daveshorts

• Moderator
• Neilep Level Member
• Posts: 2583
• Physics, Experiments
##### Empty Can (Air Pressure = 0)
« Reply #8 on: 24/01/2008 14:43:13 »
The car vacuum is just a fan, but air will only move if there is a pressure difference, so the fan produces a pressure difference. A proper vacuum cleaner will produce about a tenth of an atmosphere which is about a tonne per square metre. A car vacuum will probably produce considerably less.

#### lyner

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #9 on: 24/01/2008 18:12:25 »
bat, any difference in pressure could be called a 'vacuum' by a salesman!
How much actual force do you need? You can use daveshorts' figures to see what area you would need for your purpose.
A car vacuum cleaner works the same as a hoover- it uses a fan to 'push' air out of a space and, thus, reduces the pressure in that space. Air rushes in, carrying dirt etc and goes into the bag downstream of  the fan.
« Last Edit: 24/01/2008 18:51:55 by sophiecentaur »

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« Reply #10 on: 26/01/2008 08:41:05 »
I got it, is that possible to do something to the air particles so it moves to another side or making pressure low by doing something on the air particles?like heating or any other operation?

#### lyner

• Guest
##### Empty Can (Air Pressure = 0)
« Reply #11 on: 26/01/2008 19:20:07 »
You can hear air up and it will go up a chimney. Air will flow into the room through gaps in the windows- just a small pressure difference.

#### bat

• First timers
• Posts: 6
##### Empty Can (Air Pressure = 0)
« Reply #12 on: 10/04/2011 13:16:25 »
Just reached this post of mine after all these years, I feel bad I didn't thank you guys for your help.
So thanks everyone.

#### The Naked Scientists Forum

##### Empty Can (Air Pressure = 0)
« Reply #12 on: 10/04/2011 13:16:25 »