# The Naked Scientists Forum

### Author Topic: How much does air weigh?  (Read 4531 times)

#### neilep

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##### How much does air weigh?
« on: 13/08/2007 20:12:34 »
Dear Air Airxperts !!

As I understand it (a caper in itself !!) there's about 15lbs of air (airxperts please confirm) per square inch or something on my head yes ?

Surely that applies to when I'm outside eh ?

So, how come I am not vastly lighter on the weighing scales when inside and the roof of my home is supporting all the air weight ?

Airducate me will ya ?

« Last Edit: 14/11/2008 22:59:48 by chris »

#### another_someone

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##### Re: How much does air weigh?
« Reply #1 on: 13/08/2007 20:31:12 »
I doubt the roof of your house could support the weight of the air above (at 15 lb per square inch, and your roof maybe covers around 70,000 square inches, then that is over a million pounds of weight on your roof).

The fact is that the air leaks into your house, so the weight pressing down on your roof is balanced by the air that leaked into the house pushing the roof up as well.

That air that is pushing the roof up against the downward pressure of air, will also be pushing against your body.

#### neilep

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##### Re: How much does air weigh?
« Reply #2 on: 13/08/2007 20:41:46 »
THANK YOU GEORGE,

What about if I was in an airtight room ?

#### another_someone

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##### Re: How much does air weigh?
« Reply #3 on: 13/08/2007 20:58:19 »
THANK YOU GEORGE,

What about if I was in an airtight room ?

An airtight room would not make much difference (since the air would already have leaked in), but an evacuated room, that has no air in it, would just implode under the weight of the air pressing in from the outside.

#### lyner

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##### Re: How much does air weigh?
« Reply #4 on: 15/08/2007 16:48:20 »
Air is pushing your body from all directions. You are totally acclimatised to this so you don't notice it. The forces, however, don't, in fact, balance out.
The forces on your bottom half ( effectively pushing upwards)  are, in fact, slightly greater than the forces on your upper half (effectively pushing down). This causes upthrust which is measurable but tiny.  You weigh a tiny bit less than you would in a vacuum.
When you swim, the water, being much more dense than air, does the same thing but with enough upthrust for you to float.
It's wierd that, when you step into water, you are not really aware of the pressure around your leg but, if you are wearing 'wellies' you are very much aware of this pressure - I think that this is because  the rubber is a bit rigid  and the squeezing forces are not uniform around your calf and are more  noticeable. Kids love stepping into puddles because of this - well - I did!

#### neilep

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##### Re: How much does air weigh?
« Reply #5 on: 15/08/2007 19:49:33 »
THANK YOU sophiecentaur,

This site becomes a void without the exceptional people who take their time to visit here and go to the trouble to post/answer like you have.

Thank you...thank you all !

#### The Naked Scientists Forum

##### Re: How much does air weigh?
« Reply #5 on: 15/08/2007 19:49:33 »