# The Naked Scientists Forum

### Author Topic: Weight In a Vacuum !  (Read 17274 times)

#### neilep

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##### Weight In a Vacuum !
« on: 14/09/2006 17:25:41 »
Do things get heavier in a vacuum ?..or lighter ?

If I was to put some weighing scales in a vaccumm bottle thingy and then took out the air...would I see the scale go up or down ?
..or stay the same..?

Ta

Neil

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#### Karen W.

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##### Re: Weight In a Vacuum !
« Reply #1 on: 14/09/2006 18:36:52 »
Would it not work like gravity? The higher up into the atmosphere you get the less air, so you become lighter so I would say you take out the air the object should become lighter, just as if it had reached space, certainly not enough to float, but maybe enough to bring the weight ever so slightly down! So the scale should go down, air should have weight so taking it out should lower the scale.. Yep thats my story and I am sticking to it!!We will see if I have learned anything on this site!LOL

Karen

#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #2 on: 14/09/2006 21:51:25 »
A body's weight or mass doesn't change in the presence of air or not. The problem is that scales actually don't measure weight (or mass). What they measures is the difference between the body's weight and its upward Archimedes' push made by air on it.

So, in the void, your scale would give you an higher value for your weight, that is, your real weight. We all think our weight is less than what really is!

#### neilep

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##### Re: Weight In a Vacuum !
« Reply #3 on: 14/09/2006 22:50:12 »
THANK YOU ALBERTO !

Fascinating stuff....so.....in a  vacuum the scales would remain the same ...the only difference I would see is if I actually weighed something ?

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#### Karen W.

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##### Re: Weight In a Vacuum !
« Reply #4 on: 15/09/2006 02:45:59 »
I am confused!!

Karen

#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #5 on: 15/09/2006 08:26:55 »
quote:
Originally posted by Karen W.

I am confused!!
Think about an air-ballon and how much it would "weight" according to a scale, in presence of air, or in the void: in the void the scale would give you its real weight, but in presence of air, it would give you a much less value; if there is helium inside the ballon, it would give you a negative value! (That is, the ballon is pushed up, instead of down).

#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #6 on: 15/09/2006 08:28:07 »
quote:
Originally posted by neilep

THANK YOU ALBERTO !

Fascinating stuff....so.....in a  vacuum the scales would remain the same ...the only difference I would see is if I actually weighed something ?
Exactly.

#### eric l

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##### Re: Weight In a Vacuum !
« Reply #7 on: 15/09/2006 16:55:52 »
First question :  are the scales you use modern electronic scales based on load cells, or are they the more or less antique stuff with weights on one scale and the object on the other.
In the fist case (with the load cells) your reading will increase with increased vaccuum.  The upward force, due to Archimedes and his law, will decrease because the density of the surrounding fluid (i.e. air) decreases.
In the second case, it will depend on the density of the object compared to the density of the weights.  Example :  you have one kg of cork on the object scale, and a 1 kg copper weight on the other.  Since the cork displaces more air than the copper (for the same weight), the upward force on the cork will be greater.  If you see the scales in equilibrium, the actual MASS of the cork will be greater than the mass of copper.  If you put the scale in vaccuum the scale will tip over to the cork side.
On the other hand, if you increase the air pressure (10fold for example) the scales will tip over to the side of the copper weights.

#### neilep

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##### Re: Weight In a Vacuum !
« Reply #8 on: 15/09/2006 20:10:33 »
THANK YOU ERIC...this is really interesting stuff... I must try and get my head around it. I suppose I ought to start by figuring out what the Archimedes law is all about..seems I ought to sneak back into school with my son next week......Thank you very much.

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#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #9 on: 16/09/2006 08:37:31 »
quote:
Originally posted by neilep

THANK YOU ERIC...this is really interesting stuff... I must try and get my head around it. I suppose I ought to start by figuring out what the Archimedes law is all about..seems I ought to sneak back into school with my son next week......Thank you very much.
Archimedes law: a body immersed in a fluid (e.g. air) receives an up push equal to the weight of the displaced fluid.

#### Bass

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##### Re: Weight In a Vacuum !
« Reply #10 on: 16/09/2006 16:43:46 »
WOW!  So according to Achimedes, the larger I get, the more upward pressure will be exerted--> the less I will weigh.  Think I'll polish off that 4th (urp) cheeseburger now...

Subduction causes orogeny.

#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #11 on: 17/09/2006 10:40:43 »
quote:
Originally posted by Bass

WOW!  So according to Achimedes, the larger I get, the more upward pressure will be exerted--> the less I will weigh.  Think I'll polish off that 4th (urp) cheeseburger now...
Yes, but, unfortunately, your cheeseburger's metabolic products/compounds have an average density (mass/volume) higher than air's density, so the increase in your real weight is more than the increase in your Archimede's upward push; so, the scale will sign an higher value. (But you already know it, of course!)

Anyway, instead of cheeseburger, you could try with an hydrogenburger!
« Last Edit: 17/09/2006 10:44:53 by lightarrow »

#### Karen W.

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##### Re: Weight In a Vacuum !
« Reply #12 on: 17/09/2006 17:36:35 »
Interesting, but confusing, I think I had it backwards for some reason... I am way off!

Karen

#### neilep

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##### Re: Weight In a Vacuum !
« Reply #13 on: 17/09/2006 19:48:54 »
THANK YOU ALBERTO for the definition of Archimdes Law....I'm so relieved because I just tried on my sons school outfit and I don't half look silly in it !!..

Burger King rules !!

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#### Bass

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##### Re: Weight In a Vacuum !
« Reply #14 on: 16/09/2006 16:43:46 »
WOW!  So according to Achimedes, the larger I get, the more upward pressure will be exerted--> the less I will weigh.  Think I'll polish off that 4th (urp) cheeseburger now...

Subduction causes orogeny.

#### lightarrow

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##### Re: Weight In a Vacuum !
« Reply #15 on: 17/09/2006 10:40:43 »
quote:
Originally posted by Bass

WOW!  So according to Achimedes, the larger I get, the more upward pressure will be exerted--> the less I will weigh.  Think I'll polish off that 4th (urp) cheeseburger now...
Yes, but, unfortunately, your cheeseburger's metabolic products/compounds have an average density (mass/volume) higher than air's density, so the increase in your real weight is more than the increase in your Archimede's upward push; so, the scale will sign an higher value. (But you already know it, of course!)

Anyway, instead of cheeseburger, you could try with an hydrogenburger!
« Last Edit: 17/09/2006 10:44:53 by lightarrow »

#### Karen W.

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##### Re: Weight In a Vacuum !
« Reply #16 on: 17/09/2006 17:36:35 »
Interesting, but confusing, I think I had it backwards for some reason... I am way off!

Karen

#### neilep

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##### Re: Weight In a Vacuum !
« Reply #17 on: 17/09/2006 19:48:54 »
THANK YOU ALBERTO for the definition of Archimdes Law....I'm so relieved because I just tried on my sons school outfit and I don't half look silly in it !!..

Burger King rules !!

Men are the same as women, just inside out !

#### The Naked Scientists Forum

##### Re: Weight In a Vacuum !
« Reply #17 on: 17/09/2006 19:48:54 »