Physics Question (1 Viewer)

[Mark Fitzsimmons]

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?

 

[Andrew_Sch]

No...because it's bogus.

 

[Paul McElligott]

Absolutely bogus. A pound is a pound.

 

[Hunter P]

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.

 

[Mark Fitzsimmons]

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

 

[D. Scott MacDonald]

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.

 

[Jay Heyl]

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.)

 

[Anthony_Gomez]

have some reading fun:
http://ourworld.compuserve.com/homep...ard/weight.htm

 

[Christ Reynolds]

wait, this guy is your physics TEACHER? yikes.

CJ

 

[Jagan Seshadri]

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.

-JNS

 

[Mark Fitzsimmons]

As aforementioned, they are under the same force of gravity.

 

[Jagan Seshadri]

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

-JNS

 

[Mark Fitzsimmons]

No.

 

[Yee-Ming]

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.

 

[Jagan Seshadri]

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

 

[Adam Bluhm]

I hope to hear this answer.

 

[Glenn Overholt]

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.

Glenn

 

[Kirk Gunn]

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).

 

[BrianW]

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.

 

[Jay H]

African or European feathers?



Jay