Physics Question (1 Viewer)

[Justin Lane]

However, once the feathers increase in weight, they are no longer a 'pound' of feathers. Therefore you're not comparing a pound of feathers to a pound of nails.

To take this problem one step farther, I will make the statement that we never truly realize a "pound" of anything in this world. Air pressure is always undergoing minute changes for every instant in time, even if we cannot measure these changes. With a continually random variable, in this case pressure, there is no such thing as a single value for the pressure (i.e 1 atm). What we make are reasonably accurate estimations that fit our purposes. Don't think you can ever have "exactly" one pound of anything in the real world. It is just not possible.

J

 

[Justin Lane]

Mark, the longer you wait, the more people are going to get pissed. You first put forward a question as if you didn't know the answer, then after numerous attempts at an answer you said none of them were right and revealed you knew the answer, now you're being condescending and you're withholding the answer even though most possible explainations have been tried and shot down. Just give us the answer so we can debate the validity of it.

I agree. Let us hear what your teacher has to say to determine the accuracy (or fallacy) of his reasoning through debate. If it is as earth shattering as you make it out to be, there may be a new law of nature named after your teacher next week.

J

 

[Keith Mickunas]

Justin, you could verify the weight in a pressure controlled room. Also, once you establish that a weight is one pound, then you use that weight to balance whatever you are weighing, pressure doesn't enter into it. And in this case we're talking about weighing two things and saying their not equal to each other, so pressure really doesn't enter into it, unless as you mention its constantly changing. In that case there's no reason the nails would have to weigh more than the feathers each and every time. If its a random variable that is being applied, it will both for and against the the nails on a random basis.

 

[Mark Fitzsimmons]

I want to go ahead and post the answer/solution/reasoning/whatever you want to call it, but Justin Lane just started a decent train of thought here. What he is saying is the closest to what my physics teacher has told me.

I'll post the solution later tonight, as for now, I am going to a grad party. Take care everyone.

 

[RobertR]

If the answer turns out to be something along the lines of "a pound of feathers incorporates the weight of some other substance, therefore the actual weight of the feathers per se is less than a pound", I won't consider that valid.

 

[Lew Crippen]

If the answer turns out to be something along the lines of "a pound of feathers incorporates the weight of some other substance, therefore the actual weight of the feathers per se is less than a pound", I won't consider that valid.

Nor will it be valid. I was going to comment on Justin’s observation, which has some appeal, until you consider that the pound of feathers he is considering is in fact a mixture of feathers plus (in this case) air (should that turn out to be valid)

But that was not the question as stated: a pound of feathers and a pound of nails—not less than a pound of feather plus of little of something else. The question has been put to Mark many times as whether this was some kind of standard or trick and his answer has been consistently, no.

I’m just a humble computer guy, not a physicist (though that, along with math, is what I studied in college), so I wait to learn from those more qualified.

 

[DaveGTP]

A pound is a unit of measurement. If you point at pile A and say that it weighs more than pile B (even though they both previously were measured the same, or are currently being measured as such), you could say that. However, you cannot say "1 pound of A does not equal 1 pound of B". A pound is a unit of measure and is a scientifically specific constant. If you are talking weight pounds (and not mass pounds), it includes the force of gravity in it. Only if you are talking weight-pounds vs mass-pounds could this be true. Otherwise the pound is no longer a specific measurement (more like a cubit or handsbreadth, or some other antique, inconsistent personal measurement).

As much as I am metric-impaired (like most of the US), I can't think physics and chemistry in English measures. I wish the discussion was in Metrics. The difference between mass and weight is much clearer (grams and Newtons).

5 = 5 because of what 5 is defined as. The only way for this to be not true would be to redefine 5 as something that is not constant.

 

[Joseph Howard]

I've posted my say. I know enough to sit on the sideline
and await the teacher's reasoning.

I am still thinking we are not being given the correct "picture"
of the system to analyze.

Dr. Joe

 

[BrianW]

I want to go ahead and post the answer/solution/reasoning/whatever you want to call it, but Justin Lane just started a decent train of thought here.

Way to go, Justin! Prolong our agony, why don't you?

Okay, whatever. The feathers are fluffy and incorporate air, the feathers are constantly absorbing and evaporating moisture, the nails are taking on weight by rusting even as we speak (type?), the feathers are losing weight because they contain trace amounts of Carbon 14 which emits neutrons, individual molecules of air randomly attain off-the-scale energy levels, creating occasional forces that increase or decrease the weight of both the feathers and the nails, subatomic particles within the feathers and nails are tunneling to impossibly high states of energy, or perhaps to a different universe altogether, the nails are ferromagnetic, causing them to react to movements within the Earth's magnetic field, the feathers stink and tickle, the nails are sharp and pointy... whatever.

As Dave says, 1 pound = 1 pound, by definition. Claiming that 1 pound of something doesn't actually weigh (or have the equivalent mass of) 1 pound is utter nonsense. If any of these or some similar intervening process is the answer, then I say if it's significant enough to mention, then it's significant enough to account for. If you can't account for it and ensure that "1 = 1" holds true, then it's not worth mentioning. Period. And if you cite interaction with air as a factor and not moisture absorption/evaporation, or Carbon 14 decay, or rust, or quantum tunneling, or anything else you can possibly think of, then shame on you for having such a contrived and meaningless explanation why 1 does not equal 1.

Mark, you've milked three pages out of this. It's time to come clean.

 

[Mark Fitzsimmons]

Very sorry to keep everyone waiting on this. Until Keith pointed it out to me earlier today, I was not aware that people were becoming pissed off waiting for me to post my physics teacher's explanation on why a pound of feathers weighs more than a pound of nails.

So before any further delay here we go. . .

As aforementioned this is not a question of standards or anything of the like. For this experiment we are using the definition of

1 pound =
16 ounces.
A measurement of weight.
Whereas, weight = mass * gravity

He claims that when weighed on two equally calibrated scales, here on earth, in our atmosphere, under the same force of gravity, with no wind, when both scales read one pound, there will actually be more than one pound of feathers.

He explained to me that this is because of the buoyancy of the feathers. Because, all the scale does is measure how much force is pushing down on it, and because feathers are more buoyant than nails, it will takes actually take a greater weight of feathers to create enough force to have the scale read one pound. Because a portion of the weight of each feather will be suspended by the air.

Buoyant force is a product of air, as I understand it, it is much the same thing as wind resistance.

So what if we did the measuring in a vacuum?

It seems to me that we could get a more accurate measurement of weight in a vacuum. Lets think of it this way. We start off with the two scales. Load one up with feathers and the other with nails until they both read exactly one pound in our atmosphere. Then we take both scales and move them into a vacuum where the buoyant force will be non-existent due to the absence of air. The feather scale will now read more than one pound. How much more will depend on how the feathers are arranged.

As others have pointed out, the original premise. . .

1 pound > 1 pound

is most certainly false as it is an error in logic. Yet, perhaps we shouldn't have been looking at it in that light in the first place. Because when we weigh them in our atmosphere neither really are a pound.

*And as I remember from my math conditional days, if the antecedent is false, then the conditional is true.* [see note at bottom]

So the idea here is not that we are weighing on one scale the weight of the feathers + the weight of the air. But, rather that a portion of the weight of the feathers is going to be in essence canceled due to atmospheric suspension and therefore we will have to add a larger mass of feathers to reach that mark of one pound.

The revelation I am trying to reach is that many of the formulas we use in physics are not accurate in the world we live in. (Note: I do recognize them as being close enough for government work)

I remember in geometry learning a formula. . .

height = 1/2gravity * time^2 + initial velocity * time + initial height

to show the relation of time and height of a falling object but this formula totally ignores that different objects have varying surface area to mass ratios and do in fact fall at different rates. I believe that it was Newton who said that all objects fall at the same rate. But, can you really compare the fall rate of an apple to a parachuter?

So to conclude, this isn't really a question of standards like a pound of nails not really equaling the common pound. But that the standards we do have, are not truly accurate and in order to actually weigh something. We would need to completely isolate the system to remove such interferences that cause the pound of feathers to weigh more than a pound of nails.

And an additional note, this is not a Ph.D. thesis defense, as I do not even know if this is true or not. I just took my physics teachers explanation (he didn't say much to me other than feathers and buoyancy) and the rest is my interpretation. It does seem reasonable to me that a pound of feathers weighed on a scale in our atmosphere would actually weigh more in a vacuum.

And to reiterate, my advocacy is not that one > one, but rather, according to our scales, neither really is one to begin with.

And finally, sorry once more to keep you waiting and I hope you like this as it did take me about an hour to put into words.


*Am not sure if this is valid for a situation like this one.

 

[Bryan X]

one, but rather, according to our scales, neither really is one to begin with.

The whole explanation is nonsense as far as the question is concerned, because the question clearly states one pound of each. But in the 'answer' you are just saying that under different circumstances (a vacuum) they would weigh different amounts.

If you want that answer then the question should have read something like: If a pound of feathers and a pound of nails weighed in our atmosphere are put in a vacuum, which would weigh more?

To measure something you have to keep everything relative and constant. You have to decide if you are going to weigh in a vacuum, in the atmosphere, whatever. Then you have to take your measurements.

All you are doing is basically saying one pound doesn't equal one pound because you can change the environment.

 

[Mark Fitzsimmons]

Did you even read it?

I clearly said that my advocacy is not to prove that 1 is greater than 1.

Is that what you expected me to prove there? We both know that is impossible.

I was discussing a characterisic of our world and the behavior of matter that many people ignore or are unaware of.

 

[Mark Fitzsimmons]

Way to go and edit your post after I call you on your oversight. Skimming never gets you the whole picture.

All I am asking is for you to have an open mind and think divergently.

 

[Bryan X]

Yes I read your whole post. More than once.

I was discussing a characterisic of our world and the behavior of matter that many people ignore or are unaware of.

But did you read my post? As I said, to measure something you have to take out the variables and choose an environment to take your measurements in. Obviously if you change the environment AFTER you've taken your measurements you may get different results. There's nothing difficult to understand about that.

 

[BrianW]

if it's significant enough to mention, then it's significant enough to account for.

I stand by that statement. If something prevents a pound of feathers from being an actual pound of feathers, then account for it in your measurements so that what you say it is, is actually what it is. And the problem, as originally stated, identified "a pound of feathers," not "a pound of feathers without accounting for the bouyancy due to surrounding air. What else can we assume but that it is a pound of feathers?

It simply will not do to have our nation's top scientists, theoretical physicists, philosphers, and leading edge researchers running around in their lab coats tentatively saying, "When you say, 'a pound of feathers,' do you mean 'a pound of feathers,' or do you mean 'a REAL pound of feathers'?"

 

[Bryan X]

Way to go and edit your post after I call you on your oversight.

Don't get too high on yourself. Consider the fact that I was editing my post as you were creating yours.

 

[Mark Fitzsimmons]

But did you read my post?

Yes, and I posted before your edit.


And way to go Bryan, you are learning that when the environment changes the results change. But the idea is that in our world, because we do not live in a vacuum, the true weight of what we perceive as a pound of feathers is in fact heavier than a pound of nails.

(Edit: Changed spelling to Brian to Bryan)

 

[Mark Fitzsimmons]

Don't get too high on yourself. Consider the fact that I was editing my post as you were creating yours.

According to the HTF timestamp, I posted four minutes before you edited.

 

[Bryan X]

Yes, and I posted before your edit.

Yes, but I hadn't read it yet.

Don't get all pissy at me because the answer didn't live up to the hype. Like I said more than once, you aren't
revealing anything that everyone here doesn't already know. Environment can affect measurements.

 

[Bryan X]

According to the HTF timestamp, I posted four minutes before you edited.

You know, it does take me a few minutes to get to the edit screen, edit my post, and re-read it to verify I said everything (which I should have done initially).