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Physics Question (1 Viewer)

Chris Farmer

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Brian, while what you said is true (an inflated balloon will weigh more then an uninflated balloon), this is due to the composition of the air being breated into the balloon. Normal air contains abotu 79% nitrogen, 21% oxygen, and elss then 1% trace gases, like carbon dioxide and water vapor. The air you breathe our as you inflate the balloon is much much richer in carbon dioxide and other "heavier" gases, so it is negatively bouyant compared to normal atmorpheric air. If you used a compresor to inflate the balloon with atmospheric air, it would weigh the same as a uninflated balloon, although the masses would obviously be different.

And yes, this is a standards question, some metals for whatever reason use a different meaning of pound then what is normally thought of. It's stupid and a trick question, and I don't remember the details, but there you have it.
 

BrianW

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Brian
Chris, that's an excellent explanation of why "balloon air" is heavier than "regular air." But I do take issue with one thing you said:
If you used a compresor to inflate the balloon with atmospheric air, it would weigh the same as a uninflated balloon, although the masses would obviously be different.
This is actually not true. (About the weights being the same, that is. You're correct about the masses being different.) The reason is precisely because you must use a compressor (or similar device) to get air into the latex balloon. Though it wouldn't be as heavy (weighty) as an identical balloon filled with exhaled air for the reasons you indicate, the elasticity of the balloon slightly compresses the inside air, making it more dense (thus heavier) than surrounding air. (This is why I specified a latex balloon instead of a mylar balloon, which can be filled for most of its volume without compression. :))

If this is actually a standards question, then someone's gonna pay...
 

Tony Whalen

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Maybe you should ask him how much a pound of horsesh** weighs.
:laugh: :laugh: :laugh:

I'm waiting to see your teacher's "answer" on this... sounds like crap to me. A pound is a pound, under the conditions described. UNLESS it's a trick question somehow...
 

Hunter P

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Here are excerpts from Anthony_Gomez's link:



From this we can conclude that clearly Mark's Physics teacher is the blond ponytail guy from the movie Good Will Hunting.
 

Rob Gardiner

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Mark, a question:

Does your physics teacher offer any SUPPORT for WHY a pound of feathers weighs more? Or does he simply make the assertion and insist that it is true?
 

Chris Farmer

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Good point Bryan. I'd only considered compositional factors and completely forgotten to factor in densiteies. You're right of course, the increased density of the inflated balloon would cause it to weigh more, even if it was atmospheric air rather then exhalations.
 

John Miles

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Jan 16, 2000
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The answer is incorrect; a 16-ounce pound of nails will weigh more than a 16-ounce pound of feathers resting on the ground nearby.

Why? Because the bulk of the feathers will be slightly farther from the center of the Earth than the bulk of the nails.
 

andrew markworthy

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Because the bulk of the feathers will be slightly farther from the center of the Earth than the bulk of the nails.
True, but only assuming that the nails and feathers are piled up in a particular way.

This isn't a question with a linguistic twist, is it? 'Pound' could mean as in a 'dog pound' - assuming this to be true, then should someone be insane enough to build two pounds of identical dimensions, one out of nails, the other out of feathers, of course the nails one would weigh more. Likewise if 'pound' means 'hit', then being hit with a bag of nails would exert far more force than a bag of feathers of the same size.

I'm thinking too hard again, aren't I?
 

Mark Fitzsimmons

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And yes, this is a standards question
Wrong. This is not a standards question. Nor is it a play on words. He means pounds as a measurement of weight (16 ounces), not dog pounds, nor British pounds or anything of the like.

My teacher has explained why he feels a pound of feathers weighs more than a pound of nails and after running it through my head for the past week or so, I am begining to believe him.

I will give his explanation on this eventually. I think we have a Ph.D. in physics guy on the board here somewhere, I'm waiting for him to chime in and hear what he has to say. Or if someone says anything remotely close to his reasonings I'll chime in then. Until that time, keep guessing.
 

Jagan Seshadri

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I see. Well, while we're waiting, chew on this! :)

"Proof" that 1 + 1 = 1

a = 1
b = 1

a = b
a^2 = b^2
a^2 - b^2 = 0
(a-b)(a+b) = 0
(a-b)(a+b)/(a-b) = 0/(a-b)
1(a+b) = 0
(a+b) = 0
1 + 1 = 0
2 = 0
1 = 0
1 + 1 = 1

-JNS
 

Joseph Howard

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Hmmmm.... I'm a bit suspicious about the set-up of the
question without more details about some specifics.

However, I think it *is* the standards of measure
issue.

Bulk nails are measured in pennyweights. And there are
240 pennyweights per 1 "troy" pound. (which is less than
the regular 16oz = 1 pound standard used in most english
measure - the notable exceptions being gold weight measure
and pharmaceutical weight measure.)

(i.e. anybody got a 10 penny nail?)

So a "pound" of each (being in different standards) will
"weigh" differently.

That is what I suspect is going on. So grab a "pound" of
nails off the shelf at your local hardware store and put
it on a more conventional "weighing" device and it will
weigh less than an "english pound."

My best attempt that was.

A more fanciful thought below....

However, if we are talking about space-time curvature
differences because of size to density considerations of
the more dense nails' influence to space-time geometry to the
less dense feathers and their relative curvature of space-time
then maybe there could be something there as well.
Simply as we approach the nails through space-time the
warping of space-time around the nails will be a bit more
sudden (and severe) than the warping of space-time as we
approach the feathers' gravitational potential well.

And an interesting thing as well...

Lastly, shipping companies use "billable-weights" and
the feathers "because of volume" would calculate a
higher "billable weight" than the nails.


Anyway, I too am interested in the specifics of the
answer to this from the physics teacher because (I hope)
that there needs to be a bit more to it than what started
this thread. (ie.. assumptions and boundaries declared.)

Dr. Joe
 

Joseph Howard

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Sep 10, 1997
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More info for those inclined to work out the conversions.

English Weights:

The "Grain"
The basic unit of weight in the imperial system. There are 5760 grains to the Troy pound, and 7000 to the avoirdupois pound.

The "Ounce" - avoirdupois
Unit of weigh, equal to 437.5 grains. 16 drams to the ounce, 16 ounces to the pound.

The "Ounce" - troy
Unit of weight, equal to 480 grains, or 24 scruples. or 20 pennyweights or 8 drams. 12 ounces to the pound.

Pound - avoirdupois
Unit of weight, equal to 7000 grains, or 16 avoirdupois ounces. 14 pounds = 1 stone.

Pound - troy
Unit of weight, equal to 5760 grains, or 12 troy ounces.



Hey!! I've lost 2 "stones" lately. Cool.

Dr. Joe
 

Glenn Overholt

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Ok, I've changed my warped little mind after a bit of surfing.

The standards for nails was created in 1477 (Yikes!) At that time, you could buy 100 4d(penny) nails for 4d(penny) or 100 16d nails for a pound.

I am sure that 100 16d nails is going to weigh way more than 16 ounces.

I'm quitting and waiting for the experts to chime in, but Joseph is on the same track. I'm just late, as usual.

Glenn
 

Lew Crippen

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May 19, 2002
Messages
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Off the subject of weights, but on the subject of standards, the English pint contains 20 fluid oz., not 16. This is of importance when consuming pints of beer at your local. :)
 

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