Physics Question (1 Viewer)

[Mark Fitzsimmons]

More clarification.

We are not talking about fluid ounces.
I checked with the teacher today and it is most certainly not a standards issue.

 

[Bryan X]

Mark says:

I checked with the teacher today and it is most certainly not a standards issue.

If he explained it to you and you thought about it for a week, why would you have to check with him again that it is not a standards issue.... Something is fishy about this whole thing.

 

[andrew markworthy]

Okay, let's try again at this problem. *Subjectively*, the pound of nails will weigh more, because it's concentrated into a smaller space?

Another way of looking at it is to ask, are we just talking about feathers or nails by themselves, or are they in a container? If by themselves, then inevitably some of the feathers would float around, thereby making them lighter, since at one time it's v. unlikely that the full weight of them would be still and thus pressing downwards.

 

[Mark Fitzsimmons]

Bryan, what is wrong with that? Many people have said through this thread that they confidently feel that it is a standards issue. Since I had not talked to the teacher about standards before, I asked him just to make sure that this problem deep down is just a question of standards. I just wanted to put the uncertainty to rest. Is that a problem?

But in the end you are right, there is something fishy about this. It is quite fishy that my physics teacher can believe that two things, each weighing one pound have different weights.



andrew markworthy,

I do not think it is inevitable that some feathers would float around, that would only happen if there was wind. And for arguments sake, lets say that neither the nails or the feathers are in a container, just so people aren't questioning differences in the air contained in bags or the like.

 

[RobertR]

It seems that all the issues have been covered. If we assume that different meanings aren't being applied to the word "pound", and we're talking only about the substances in question and not different gravities, containers, or wind velocities, etc., then they have to weigh the same.

 

[Bryan X]

Bryan, what is wrong with that?

Nothing 'wrong' with that. Just that it makes me feel like the answer is perhaps based on 'a certain point of view' or some other 'trick' answer. If it were a straight answer based strictly on physics and not some 'trick' then I wouldn't think you would need to 'run it through your head' for a week.

This all leads me to believe that there is some odd twist to it.

 

[Mark Fitzsimmons]

Hearing his answer, I can assure you that it has nothing to do with a certain point of view or is it a trick answer. The answer sounds physically reasonable, I just do not know if it is right or not. That is why I am asking for input from other users.

 

[Keith Mickunas]

Consider this approach, if I take a properly calibrated scale, and pile feathers on it until it shows exactly 1 pound, then I have 1 pound of feathers. Then I use that same scale and add nails to it until it shows 1 pound, then I'll have 1 pound of nails. They will be equal. By the definition of 1 pound of X, they must be. You're saying that its not a standards issue, so how could it possibly pass my test if they aren't equal?

 

[Adam Bluhm]

I just want the freakin' reasoning already.

 

[Lew Crippen]

I thought some about this last night while watching my Dallas Mavericks go down to defeat. I admit that this may have caused me to not be able to think clearly, but since you maintain that this is not a standards issue nor a definitional issue, I, along with many others await your specifics.

Somehow there has to be more than the information we have been given. Otherwise I’m on the ‘pound is a pound’ side. I’m not a physicist, but I thought that I had a good layman’s understanding of these kinds of things. Apparently not, so post already. Please.

 

[Justin Lane]

Hearing his answer, I can assure you that it has nothing to do with a certain point of view or is it a trick answer. The answer sounds physically reasonable, I just do not know if it is right or not. That is why I am asking for input from other users.

So what's the answer Mark? Kind or hard to ascertain if your teacher's answer is right or wrong if we don't know what he told you.
J

 

[Bryan X]

Hearing his answer, I can assure you that it has nothing to do with a certain point of view or is it a trick answer. The answer sounds physically reasonable, I just do not know if it is right or not. That is why I am asking for input from other users.

Exactly. Let's stop playing around and just give us the answer. Then we can go about trying to determine if it is correct or not.

 

[Mark Fitzsimmons]

I am still trying to hear more ideas before posting my teachers reasoning.

I promise a lengthy, well written post when I do reveal his thoughts and my interpretation.

 

[Bryan X]

I am still trying to hear more ideas before posting my teachers reasoning.

I promise a lengthy, well written post when I do reveal his thoughts and my interpretation.

This still sounds like an answer 'from a certain point of view' not a physics 'fact'.

Look at it this way. If one weighs more or less than the other then you are not comparing 1 pound to 1 pound therefore the question is invalid.

 

[Justin Lane]

I will take a shot at the answer even though Mark is leaving us all in suspense.

Weight measured in lb or N, is a measurement of the force required to pulll a body towards a nearby astronomical body (in our case the earth). Described by the equation W=m*g

What you everyone is forgetting is that a pound of feathers also contains a large amount of air as its content. Air is a compressable gas which means its density can can change as the atmospheric pressure increases.

Density can be described as p (rho)=m/V. For example, at 20 C and 1 atm of pressure, the density of air is 1.21 kg/m^3 while at 20C and 50 atm air has a density of 60.5 kg/m^3.
By increasing the pressure around a pound of feathers, you will increase the density of the air which makes up the pound of feathers, increasing the mass, and thus increasing the weight.

Kind of a tricky question, but after thinking about it, I came to the solution quite easily. When pressure increases after the initial measurement of weight, the same "pound" of feathers will indeed weigh more than the "pound" of nails.

J

 

[Bryan X]

Kind of a tricky question, but after thinking about it, I came to the solution quite easily. When atmospheric pressure increases after the initial measurement of weight, the same "pound" of feathers will indeed weight more than the "pound" of nails.

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.

 

[Mark Fitzsimmons]

Bryan, you're stating the obvious. If this was a physics fact then I am sure that Dr. Howard would have confirmed it.

I posted this thread because I did not believe him and wanted to check with the community to see if anyone else was in the same camp as him. So far, I haven't found anyone.

I did not post this to try and preach this as fact, I posted seeking the solution and opinions.

He believes it is fact, so I am just going to post his rational; which I now believe to be an opinion, since it is certainly not the common view.

What I can tell you is that his explanation seems logical (in part) to me. For that, I believe it may even be true 'from a certain point of view' as you put it.

But we'll see. . . just keep an open mind and the answer may intrigue you. It may possibly change your perspective of physics and the world around you. But in order for any of this you must first lose the cynical attitude and create an open mind.

 

[Bryan X]

But we'll see. . . just keep an open mind and the answer may intrigue you. It may possibly change your perspective of physics and the world around you. But in order for any of this you must first lose the cynical attitude and create an open mind.

I'm certainly open to any answers. I've been wrong before... just ask my wife.

 

[Justin Lane]

But we'll see. . . just keep an open mind and the answer may intrigue you. It may possibly change your perspective of physics and the world around you. But in order for any of this you must first lose the cynical attitude and create an open mind.

This better be a very good answer, and not some second rate high school physics teacher trying to trick his students with a cute response.

J

 

[Keith Mickunas]

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.