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Physics Question


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155 replies to this topic

#1 of 156 Mark Fitzsimmons

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Posted May 28 2003 - 11:33 AM

My physics teacher claims that a pound of feathers weighs more than a pound of nails. I think that they both weigh a pound. . .

Can any physics gurus shine any light on this?
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#2 of 156 Andrew_Sch

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Posted May 28 2003 - 11:38 AM

No...because it's bogus.
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#3 of 156 Paul McElligott

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Posted May 28 2003 - 11:54 AM

Absolutely bogus. A pound is a pound.
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#4 of 156 Hunter P

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Posted May 28 2003 - 12:18 PM

I suppose it is possible since a pound is the measure of gravitational force on an object. If the nails were on the Moon and the feathers on the Earth then the statement would be true.

If they are side by side then there is no way that one is heavier.
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#5 of 156 Mark Fitzsimmons

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Posted May 28 2003 - 12:20 PM

Even if they are side by side here on earth, so under the same amount of gravity. He still claims the feathers weigh more.
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#6 of 156 D. Scott MacDonald

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Posted May 28 2003 - 12:29 PM

A pound is a unit or weight. Hence, a pound of anything is equal to a pound of anything else (at least in weight). If one weighed more than the other, then one of them wouldn't be a pound.
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#7 of 156 Jay Heyl

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Posted May 28 2003 - 12:53 PM

I've heard it said that a pound of feathers weighs more than a pound of gold. I've never heard nails mentioned in relation to feathers.

The feathers/gold thing is a trick question. Feathers, like most common substances, are weighed using the avoirdupois system of weights, in which a pound contains 16 ounces. Gold, and most other precious metals, is typically weighed using the troy system, in which a pound contains 12 ounces. (Apologies to the metrically-enabled for whom I'm sure this makes even less sense than to those of us encumbered by an antiquated system of measure.)

#8 of 156 Guest_Anthony_Gomez_*

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Posted May 28 2003 - 01:06 PM

have some reading fun:
http://ourworld.comp....ard/weight.htm

#9 of 156 Christ Reynolds

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Posted May 28 2003 - 01:21 PM

wait, this guy is your physics TEACHER? yikes.

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#10 of 156 Jagan Seshadri

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Posted May 28 2003 - 01:54 PM

Weight is different than mass.

A pound is a force unit that depends on the gravitational (and other) acceleration. Mass (i.e. a kilogram) is independent of accelerations, and is more a measure of 'matter'.

(Think about this: when you're in an elevator, your weight changes as you accelerate upwards or downwards, even though your mass remains constant.)

Assuming that the pound of feathers and the pound of nails are weighed under the same gravitational (and other) acceleration, then they both 'weigh' the same.

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#11 of 156 Mark Fitzsimmons

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Posted May 28 2003 - 01:57 PM

As aforementioned, they are under the same force of gravity.
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#12 of 156 Jagan Seshadri

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Posted May 28 2003 - 01:59 PM

Well, is one being weighed in an accelerating frame of reference such as an....elevator? That would change things.

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#13 of 156 Mark Fitzsimmons

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Posted May 28 2003 - 02:34 PM

No.
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#14 of 156 Yee-Ming

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Posted May 28 2003 - 02:43 PM

I vaguely recall some form of trick question based on this, the twist being that a bag of a pound of feathers contained more air than a bag of a pound of nails would, and hence would be marginally heavier. But that's a fallacious reason anyway.

#15 of 156 Jagan Seshadri

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Posted May 28 2003 - 02:58 PM

The problem with the air-in-the-bag argument is that the air contributes no weight since it is neutrally buoyant in the air outside the bag.

Either your Physics teacher made a mistake or the answer to this is going to be corny!

-JNS

#16 of 156 Adam Bluhm

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Posted May 28 2003 - 03:09 PM

I hope to hear this answer.
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#17 of 156 Glenn Overholt

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Posted May 28 2003 - 03:21 PM

It is probably true. A pound of nails doesn't weigh 16 ounces, as it is on a different scale, just like gold is.

You should look up how nails are weighed, legally. I'm not sure, but an 8d nail can only have a certain number until it reaches a 'nail's pound'. Maybe you can ask a carpenter.

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#18 of 156 Kirk Gunn

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Posted May 28 2003 - 04:49 PM

So this is really a Standards question and not a physics inquiry ? Guess it's good for a teacher to bring this up since not adhering to proper standards can really muck things up (original Hubble Telescope mirror for example).

#19 of 156 BrianW

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Posted May 29 2003 - 12:01 AM

Quote:
The problem with the air-in-the-bag argument is that the air contributes no weight since it is neutrally buoyant in the air outside the bag.
Ah, but if you show that two identical latex balloons have identical mass when deflated, when one is inflated, it can be shown to weigh more than the deflated balloon (with no tricks like using accelerating reference frames or weighing on different planets). How can this be true if what you said is correct?

(Hint: What you said about the air in feathers is correct.)

I think the feathers weigh more because they absorb moisture. Posted Image
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#20 of 156 Jay H

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Posted May 29 2003 - 12:58 AM

African or European feathers?

Posted Image

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