Orchid XP v8 wrote:
> Yeah, because a high vacuum is easy to come by. Oh, wait...

Well, yeah, it is.  It's called a bell jar.

http://www.youtube.com/watch?v=_XJcZ-KoL9o
(Note - the next video after the one I posted.)

You can go to edmond's scientific and buy bottles of vacuum for like a 
quarter each, too.  It's not like you need interstellar-space vacuum to 
prove the point.

-- 
Darren New, San Diego CA, USA (PST)
   Forget "focus follows mouse." When do
   I get "focus follows gaze"?

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>> Yeah, because a high vacuum is easy to come by. Oh, wait...
> 
> Well, yeah, it is.  It's called a bell jar.

You'd need a pretty damned big bell jar to drop an object any 
significant distance.

> You can go to edmond's scientific and buy bottles of vacuum for like a 
> quarter each, too.

Really?


The London Science Museum has a bell inside a jar with a vacuum pump. 
But last I checked, a pump powerful enough to create anything you could 
describe as "a vacuum" is an extremely expensive piece of scientific 
equipment.

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Stephen wrote:
> 
> Well I probably don’t think of hp as being anything as other than what
> non-technical people say. Who knows what work a horse can do nowadays?
> If the health and safety or animal welfare people allow it ;)
> 

In that, my friend, you are absolutely right.

-Aero

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Invisible wrote:
> You'd need a pretty damned big bell jar to drop an object any 
> significant distance.

Somewhat larger than the distance it takes to see a feather and a ball 
bearing falling at different speeds in atmosphere.

>> You can go to edmond's scientific and buy bottles of vacuum for like a 
>> quarter each, too.
> 
> Really?

Yes. Ever get blood drawn? How do you think that works?

> But last I checked, a pump powerful enough to create anything you could 
> describe as "a vacuum" is an extremely expensive piece of scientific 
> equipment.

http://www.google.com/products?q=vacuum+pumps+for+sale

Even the $25 pump gets you down to 29" of vacuum.

-- 
Darren New, San Diego CA, USA (PST)
   Forget "focus follows mouse." When do
   I get "focus follows gaze"?

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> Yes. Ever get blood drawn? How do you think that works?

Presumably they just use a syringe. I wasn't looking at the time; I was 
in far too much pain...

>> But last I checked, a pump powerful enough to create anything you 
>> could describe as "a vacuum" is an extremely expensive piece of 
>> scientific equipment.
> 
> http://www.google.com/products?q=vacuum+pumps+for+sale
> 
> Even the $25 pump gets you down to 29" of vacuum.

Interesting. I wonder what it costs to buy a large container than can 
withstand several thousand Newtons of force trying to crush it...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
>> Even the $25 pump gets you down to 29" of vacuum.
> 
> Interesting. I wonder what it costs to buy a large container than can 
> withstand several thousand Newtons of force trying to crush it...

Really, not all that much. You're really only talking about one atmosphere. 
A soda can will keep that much *in*.

-- 
Darren New, San Diego CA, USA (PST)
   Forget "focus follows mouse." When do
   I get "focus follows gaze"?

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>>> Even the $25 pump gets you down to 29" of vacuum.
>>
>> Interesting. I wonder what it costs to buy a large container than can 
>> withstand several thousand Newtons of force trying to crush it...
> 
> Really, not all that much. You're really only talking about one 
> atmosphere. A soda can will keep that much *in*.

Hmm, 1 atmosphere. That's about 100 kPa. Over a 100 cm^2 area, that's 
about 1,000 N. Sounds like a pretty big force to me...

Then again, I was under the impression that a soda can only holds about 
0.01 atm of pressure. (1 atm is a LARGE pressure, after all.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
> (1 atm is a LARGE pressure, after all.)

No, it's really not. Your car tires hold twice that in a safety-critical 
application. A scuba tank easily holds 200 times that much. How much 
pressure do you think is on the glass of a huge aquarium (like in an 
aquarium museum type building)? Submarines? It's not really that tough to 
hold out dozens of atmospheres, let alone one.

-- 
Darren New, San Diego CA, USA (PST)
   Forget "focus follows mouse." When do
   I get "focus follows gaze"?

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> Hmm, 1 atmosphere. That's about 100 kPa. Over a 100 cm^2 area, that's 
> about 1,000 N. Sounds like a pretty big force to me...

Most standard drinks bottles seem to be able to take about 10 atmospheres 
pressure:

http://home.people.net.au/~aircommand/procedures.htm

Your mains water pressure is probably around 5 atmospheres.

You really don't need very thick walls to enclose 1 atmosphere safely.

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On Mon, 18 Jan 2010 08:58:04 +0100, scott wrote:

> Most standard drinks bottles seem to be able to take about 10
> atmospheres pressure:

Interestingly, I was watching Mythbusters last night; one of the myths 
they were testing was a "water rocket" myth that involved 3L soda bottles.

They pumped them up to around 90 PSI before they had critical failures.

That's about 400 N per square inch....And that's a soda bottle. :-)

Jim

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