Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

I guess within the atmosphere, under the same pressures, a kilogram of feathers is a kilogram at those conditions

but a compensated kilogram of feathers would be different

if any difference, possibly it may come down to if there are any pockets of air (whatever gasses) that are less dense than atmospheric gasses at the measuring place, or altitude mostly, + local air pressure I guess

dunno, interesting question

we mean it’s far less measurably significant but if they’re going to get all technical then when gravitation can be modelled as an inverse square force equivalent, it seems unlikely that kilograms of materials of different density or even just spatial distribution regardless of density will actually weigh the same anyway

the answer i’d guess is probably in the proposition of why you wouldn’t use a kilogram of feathers as the standard, you know there in the national standards laboratory, whatever it’s called, the standards for weights

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

The Rev Dodgson said:

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

Probably talking about an ideal 10kg of feathers in an ideal gas environment.

Peak Warming Man said:

The Rev Dodgson said:

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

Probably talking about an ideal 10kg of feathers in an ideal gas environment.

we have spherical cows for that scenario.

The Rev Dodgson said:

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

So the actual proposition is “feathers measured to have mass M by device D in circumstances C would weigh the same as steel measured to have mass M by device E in circumstances B, when weighed using method W“¿

Well, unless D = E and C = B and W = {D, C} or equivalent then in general that seems unconvincing.

Bogsnorkler said:

Peak Warming Man said:

The Rev Dodgson said:

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

Probably talking about an ideal 10kg of feathers in an ideal gas environment.

we have spherical cows for that scenario.

Seems legit’, these cows look fairly spherical* to us.

*: well, fairly circular in their 3D projection

https://veteriankey.com/evaluation-of-in-vivo-derived-bovine-embryos/

Evaluation of In Vivo-Derived Bovine Embryos

SCIENCE said:

The Rev Dodgson said:

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

So the actual proposition is “feathers measured to have mass M by device D in circumstances C would weigh the same as steel measured to have mass M by device E in circumstances B, when weighed using method W“¿

Well, unless D = E and C = B and W = {D, C} or equivalent then in general that seems unconvincing.

I suspect the actual proposition is a good bit simpler:

If two samples of different materials weigh the same, then they weigh the same.

I mean if you weighed them in a vacuum then sure, they’d be the same.

dv said:

I mean if you weighed them in a vacuum then sure, they’d be the same.

Only if they had the same mass.

How are these samples of equal mass prepared?

By the way, the accepted Internet density of feathers is 0.0025.

One site even gave units (g/cm^3).

The Rev Dodgson said:

How are these samples of equal mass prepared?

Hmmmm we could weigh them.

The Rev Dodgson said:

dv said:

I mean if you weighed them in a vacuum then sure, they’d be the same.

Only if they had the same mass.

How are these samples of equal mass prepared?

By the way, the accepted Internet density of feathers is 0.0025.

One site even gave units (g/cm^3).

Note that for this purpose what matters is the density of keratin, 1300 kg per cubic metre. The fact that there is a bunch of air in a sample of feathers is not going to affect their weight after allowing for air buoyancy.

dv said:

The Rev Dodgson said:

dv said:

I mean if you weighed them in a vacuum then sure, they’d be the same.

Only if they had the same mass.

How are these samples of equal mass prepared?

By the way, the accepted Internet density of feathers is 0.0025.

One site even gave units (g/cm^3).

Note that for this purpose what matters is the density of keratin, 1300 kg per cubic metre. The fact that there is a bunch of air in a sample of feathers is not going to affect their weight after allowing for air buoyancy.

It seems I don’t follow your proposed procedure then.

Could you give us an outline?

The Rev Dodgson said:

dv said:

The Rev Dodgson said:

Only if they had the same mass.

How are these samples of equal mass prepared?

By the way, the accepted Internet density of feathers is 0.0025.

One site even gave units (g/cm^3).

Note that for this purpose what matters is the density of keratin, 1300 kg per cubic metre. The fact that there is a bunch of air in a sample of feathers is not going to affect their weight after allowing for air buoyancy.

It seems I don’t follow your proposed procedure then.

Could you give us an outline?

I haven’t specified a procedure. It’s not really relevant.

dv said:

The Rev Dodgson said:

dv said:

Note that for this purpose what matters is the density of keratin, 1300 kg per cubic metre. The fact that there is a bunch of air in a sample of feathers is not going to affect their weight after allowing for air buoyancy.

It seems I don’t follow your proposed procedure then.

Could you give us an outline?

I haven’t specified a procedure. It’s not really relevant.

How is it not relevant?

You’ll get different results depending on how you measure the mass of the samples, and how you then measure their weight.

The Rev Dodgson said:

SCIENCE said:

The Rev Dodgson said:

Haven’t seen the video, but I’m guessing by “10 kg of feathers” they mean the mass of feathers that would weigh 10 kg on a standard balance in air, so a fair bit more than 10 kg mass.

So the actual proposition is “feathers measured to have mass M by device D in circumstances C would weigh the same as steel measured to have mass M by device E in circumstances B, when weighed using method W“¿

Well, unless D = E and C = B and W = {D, C} or equivalent then in general that seems unconvincing.

I suspect the actual proposition is a good bit simpler:

If two samples of different materials weigh the same, then they weigh the same.

but kilogram is not SI weight so that can’t be the proposition

SCIENCE said:

The Rev Dodgson said:

SCIENCE said:

So the actual proposition is “feathers measured to have mass M by device D in circumstances C would weigh the same as steel measured to have mass M by device E in circumstances B, when weighed using method W“¿

Well, unless D = E and C = B and W = {D, C} or equivalent then in general that seems unconvincing.

I suspect the actual proposition is a good bit simpler:

If two samples of different materials weigh the same, then they weigh the same.

but kilogram is not SI weight so that can’t be the proposition

Sorry, I thought we were talking about an Internet video.

My mistake.

The Rev Dodgson said:

SCIENCE said:

The Rev Dodgson said:

I suspect the actual proposition is a good bit simpler:

If two samples of different materials weigh the same, then they weigh the same.

but kilogram is not SI weight so that can’t be the proposition

Sorry, I thought we were talking about an Internet video.

My mistake.

Not to worry, I think DV was just floating an idea in the first place.

Peak Warming Man said:

The Rev Dodgson said:

SCIENCE said:

but kilogram is not SI weight so that can’t be the proposition

Sorry, I thought we were talking about an Internet video.

My mistake.

Not to worry, I think DV was just floating an idea in the first place.

anyway imagine if there were things on the internet and they were wrong

SCIENCE said:

Peak Warming Man said:

The Rev Dodgson said:

Sorry, I thought we were talking about an Internet video.

My mistake.

Not to worry, I think DV was just floating an idea in the first place.

anyway imagine if there were things on the internet and they were wrong

Indeed, and in fact I thought we were discussing just such a thing.

SCIENCE said:

Peak Warming Man said:

The Rev Dodgson said:

Sorry, I thought we were talking about an Internet video.

My mistake.

Not to worry, I think DV was just floating an idea in the first place.

anyway imagine if there were things on the internet and they were wrong

we’d be here all night if something like that were to occur.

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

9.9985 vs 9.9915, yes. How accurate is your “balance beam”?

It goes without saying that atomic masses of the elements are always weighed in a vacuum.

It also goes without saying that you must always weigh things at the same location on the Earth’s surface. The acceleration due to gravity varies enormously from one place to another. To misquote Archimedes “Give me a balance beam long enough and a fulcrum on which to place it, and I shall” make a 10 kg mass weigh 1 kg.

The Rev Dodgson said:

SCIENCE said:

Peak Warming Man said:

Not to worry, I think DV was just floating an idea in the first place.

anyway imagine if there were things on the internet and they were wrong

Indeed, and in fact I thought we were discussing just such a thing.

so do they claim that kilogram is weight or does the discussion actually need to go any further

mollwollfumble said:

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

9.9985 vs 9.9915, yes. How accurate is your “balance beam”?

It goes without saying that atomic masses of the elements are always weighed in a vacuum.

It also goes without saying that you must always weigh things at the same location on the Earth’s surface. The acceleration due to gravity varies enormously from one place to another. To misquote Archimedes “Give me a balance beam long enough and a fulcrum on which to place it, and I shall” make a 10 kg mass weigh 1 kg.

I thing DV’s buoyant weight calculation for the feathers is way out.

The Rev Dodgson said:

dv said:

The Rev Dodgson said:

It seems I don’t follow your proposed procedure then.

Could you give us an outline?

I haven’t specified a procedure. It’s not really relevant.

How is it not relevant?

You’ll get different results depending on how you measure the mass of the samples, and how you then measure their weight.

The objects have a specific rest mass which does not vary. There’s only one correct mass of an object. I don’t know which methodology is used, and it doesn’t matter which is used, as long as it is a sound one.

SCIENCE said:

The Rev Dodgson said:

SCIENCE said:

anyway imagine if there were things on the internet and they were wrong

Indeed, and in fact I thought we were discussing just such a thing.

so do they claim that kilogram is weight or does the discussion actually need to go any further

The kilogram is a very widely used unit of weight.

dv said:

The Rev Dodgson said:

dv said:

I haven’t specified a procedure. It’s not really relevant.

How is it not relevant?

You’ll get different results depending on how you measure the mass of the samples, and how you then measure their weight.

The objects have a specific rest mass which does not vary. There’s only one correct mass of an object. I don’t know which methodology is used, and it doesn’t matter which is used, as long as it is a sound one.

I thought that the point was that it almost certainly wasn’t a sound one, since measuring the rest mass of a collection of feathers is actually quite difficult.

The Rev Dodgson said:

SCIENCE said:

The Rev Dodgson said:

Indeed, and in fact I thought we were discussing just such a thing.

so do they claim that kilogram is weight or does the discussion actually need to go any further

The kilogram is a very widely used unit of weight.

Well in our world which is SCIENCE, being wide is not the same as being correct, and they said the following.

Considering the necessity to put an end to the ambiguity which in current practice still exists on the meaning of the word weight, used sometimes for mass, sometimes for mechanical force;
The Conference declares

1. The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram;*
2. The word “weight” denotes a quantity of the same nature as a “force”: the weight of a body is the product of its mass and the acceleration due to gravity; in particular, the standard weight of a body is the product of its mass and the standard acceleration due to gravity;
3. The value adopted in the International Service of Weights and Measures for the standard acceleration due to gravity is 980.665 cm/s2, value already stated in the laws of some countries.**
   

What that means is, if your preferred video is pulling standard weight, then what dv says about buoyancy is irrelevant, and objects with the same mass have the same standard weight.

What it also means is, even without your preferred video pulling standard weight, then what dv says about buoyancy is still irrelevant, but objects with the same mass are unlikely to have the same weight.

As we’ve mentioned before, whether the difference is measurable is another small amount of matter.

Probably ScIeNCE put it better than me but it would be a bit naff to do an experiment that showed that when two objects balance each other on a beam they balance each other on a beam.

dv said:

Probably ScIeNCE put it better than me but it would be a bit naff to do an experiment that showed that when two objects balance each other on a beam they balance each other on a beam.

I didn’t suggest it wasn’t a bit naff.

I just suggested that quite likely that was what they were doing.

But as I haven’t actually seen the video to which you referred, I could be wrong of course.

The Rev Dodgson said:

dv said:

Probably ScIeNCE put it better than me but it would be a bit naff to do an experiment that showed that when two objects balance each other on a beam they balance each other on a beam.

I didn’t suggest it wasn’t a bit naff.

I just suggested that quite likely that was what they were doing.

But as I haven’t actually seen the video to which you referred, I could be wrong of course.

Bing found this one for me:

https://www.youtube.com/watch?v=dC_VaUhpiXY

It only has 124 views though.

But I guess if we’re doing this there would be three ways to measure something’s mass:

Carefully count the atoms and look up their masses in a table …

Apply a force and see how much it accelerates (being carefully to ensure that other forces are negligible)

Measure its gravitational force in a known gravitational field (being carefully to ensure that other forces are negligible)

dv said:

But I guess if we’re doing this there would be three ways to measure something’s mass:

Carefully count the atoms and look up their masses in a table …

Apply a force and see how much it accelerates (being carefully to ensure that other forces are negligible)

Measure its gravitational force in a known gravitational field (being carefully to ensure that other forces are negligible)

OK, looks like we are making progress here.

Let’s go for second one as it is more closely tied to the definition of mass than the third and less laborious than the first, and also doesn’t require using other people’s data.

This will require the use of an evacuated chamber of course, but we can also use that for the weight measurements, so all good.

Now is there a video where they have done this?

The Rev Dodgson said:

dv said:

But I guess if we’re doing this there would be three ways to measure something’s mass:

Carefully count the atoms and look up their masses in a table …

Apply a force and see how much it accelerates (being carefully to ensure that other forces are negligible)

Measure its gravitational force in a known gravitational field (being carefully to ensure that other forces are negligible)

OK, looks like we are making progress here.

Let’s go for second one as it is more closely tied to the definition of mass than the third and less laborious than the first, and also doesn’t require using other people’s data.

This will require the use of an evacuated chamber of course, but we can also use that for the weight measurements, so all good.

Now is there a video where they have done this?

https://www.youtube.com/watch?v=s9Zb3xAgIoY

The Rev Dodgson said:

dv said:

But I guess if we’re doing this there would be three ways to measure something’s mass:

Carefully count the atoms and look up their masses in a table …

Apply a force and see how much it accelerates (being carefully to ensure that other forces are negligible)

Measure its gravitational force in a known gravitational field (being carefully to ensure that other forces are negligible)

OK, looks like we are making progress here.

Let’s go for second one as it is more closely tied to the definition of mass than the third and less laborious than the first, and also doesn’t require using other people’s data.

This will require the use of an evacuated chamber of course, but we can also use that for the weight measurements, so all good.

Now is there a video where they have done this?

…. in the dark.

roughbarked said:

The Rev Dodgson said:

dv said:

But I guess if we’re doing this there would be three ways to measure something’s mass:

Carefully count the atoms and look up their masses in a table …

Apply a force and see how much it accelerates (being carefully to ensure that other forces are negligible)

Measure its gravitational force in a known gravitational field (being carefully to ensure that other forces are negligible)

OK, looks like we are making progress here.

Let’s go for second one as it is more closely tied to the definition of mass than the third and less laborious than the first, and also doesn’t require using other people’s data.

This will require the use of an evacuated chamber of course, but we can also use that for the weight measurements, so all good.

Now is there a video where they have done this?

https://www.youtube.com/watch?v=s9Zb3xAgIoY

OK, but what about measuring their mass and weight?

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

OK, looks like we are making progress here.

Let’s go for second one as it is more closely tied to the definition of mass than the third and less laborious than the first, and also doesn’t require using other people’s data.

This will require the use of an evacuated chamber of course, but we can also use that for the weight measurements, so all good.

Now is there a video where they have done this?

https://www.youtube.com/watch?v=s9Zb3xAgIoY

OK, but what about measuring their mass and weight?

Specific gravity?

roughbarked said:

The Rev Dodgson said:

roughbarked said:

https://www.youtube.com/watch?v=s9Zb3xAgIoY

OK, but what about measuring their mass and weight?

Specific gravity?

What about it?

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

OK, but what about measuring their mass and weight?

Specific gravity?

What about it?

I was asking you.

roughbarked said:

The Rev Dodgson said:

roughbarked said:

Specific gravity?

What about it?

I was asking you.

What are you asking me about it?

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

What about it?

I was asking you.

What are you asking me about it?

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

roughbarked said:

The Rev Dodgson said:

roughbarked said:

I was asking you.

What are you asking me about it?

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

What are you asking me about it?

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

Archimedes would know how.

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

What are you asking me about it?

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

Place feathers in vacuume chamber. Remove air. Measure volume of air removed compared to volume of vacuume chamber. The difference is the volume of the feathers.

Bogsnorkler said:

The Rev Dodgson said:

roughbarked said:

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

Archimedes would know how.

Maybe, but I have never seen any writings attributed to him on that specific subject.

Dark Orange said:

The Rev Dodgson said:

roughbarked said:

Well we know it is a way of measuring density. By floating.
You were looking at Vacuum and falling.

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

Place feathers in vacuume chamber. Remove air. Measure volume of air removed compared to volume of vacuume chamber. The difference is the volume of the feathers.

How accurately can you measure the volume of air removed though?

The Rev Dodgson said:

Bogsnorkler said:

The Rev Dodgson said:

We were looking at mass and weight.

Density doesn’t really come into it.

Also accurately measuring the volume of a collection of feathers would be pretty difficult.

Archimedes would know how.

Maybe, but I have never seen any writings attributed to him on that specific subject.

“Eureka!”

Michael V said:

The Rev Dodgson said:

Bogsnorkler said:

Archimedes would know how.

Maybe, but I have never seen any writings attributed to him on that specific subject.

“Eureka!”

You know we are talking specifically about feathers here, right?

The problem being, how do you ensure that the volume of air displaced when you do the measurement is the same as the volume removed when you evacuate the chamber?

DO’s suggestion gets around that problem very nicely, so would probably be the best approach, but I still think it would be pretty difficult.

And I still don’t know why we are doing this measurement anyway.

The Rev Dodgson said:

Michael V said:

The Rev Dodgson said:

Maybe, but I have never seen any writings attributed to him on that specific subject.

“Eureka!”

You know we are talking specifically about feathers here, right?

The problem being, how do you ensure that the volume of air displaced when you do the measurement is the same as the volume removed when you evacuate the chamber?

DO’s suggestion gets around that problem very nicely, so would probably be the best approach, but I still think it would be pretty difficult.

And I still don’t know why we are doing this measurement anyway.

DOs suggestion is just a variation of the Archimedes’ principle.

Bogsnorkler said:

The Rev Dodgson said:

Michael V said:

“Eureka!”

You know we are talking specifically about feathers here, right?

The problem being, how do you ensure that the volume of air displaced when you do the measurement is the same as the volume removed when you evacuate the chamber?

DO’s suggestion gets around that problem very nicely, so would probably be the best approach, but I still think it would be pretty difficult.

And I still don’t know why we are doing this measurement anyway.

DOs suggestion is just a variation of the Archimedes’ principle.

I didn’t suggest otherwise.

I said it gets around the problem of controlling the volume of displaced air, which is the big problem using the original Archimedes technique.

The Rev Dodgson said:

Bogsnorkler said:

The Rev Dodgson said:

You know we are talking specifically about feathers here, right?

The problem being, how do you ensure that the volume of air displaced when you do the measurement is the same as the volume removed when you evacuate the chamber?

DO’s suggestion gets around that problem very nicely, so would probably be the best approach, but I still think it would be pretty difficult.

And I still don’t know why we are doing this measurement anyway.

DOs suggestion is just a variation of the Archimedes’ principle.

I didn’t suggest otherwise.

I said it gets around the problem of controlling the volume of displaced air, which is the big problem using the original Archimedes technique.

well, when you responded with “Maybe, but I have never seen any writings attributed to him on that specific subject.” it made me think you hadn’t thought much about the actual principle. Fluids is fluids after all.

Bogsnorkler said:

The Rev Dodgson said:

Bogsnorkler said:

DOs suggestion is just a variation of the Archimedes’ principle.

I didn’t suggest otherwise.

I said it gets around the problem of controlling the volume of displaced air, which is the big problem using the original Archimedes technique.

well, when you responded with “Maybe, but I have never seen any writings attributed to him on that specific subject.” it made me think you hadn’t thought much about the actual principle. Fluids is fluids after all.

In the context being discussed, fluids is not fluids. If you measured the volume of a bunch of feathers by dunking them under water you’d get very variable results, and they’d all be very different to measurements with the DO technique.

The Rev Dodgson said:

mollwollfumble said:

dv said:

Worth a thread, maybe.

There’s a humorous video going about in which a fellow struggles with the fact that a kilogram of steel has the same weight as a kilogram of feathers.

His interlocutors try to prove the point by placing a kg of steel and a kg of feathers on either ends of a large balance beam.

Seems to me that the feathers would “weigh” less than the steel on a balance beam, or on any normal kind of scale in a terrestrial environment, due to air buoyancy.

Unless there’s something I’m misunderstanding, 10 kg of steel will, on a scale, weigh around 9.9985 kg, because the air it displaces has a mass of around 0.0015 kg.

Feathers are mostly made of keratin, which has a density of around 1300 kg per cubic metre. The air 10 kg of feathers displaces will have a mass of around 0.0095 kg, so on the scales it will weight about 9.9915 kg.

9.9985 vs 9.9915, yes. How accurate is your “balance beam”?

It goes without saying that atomic masses of the elements are always weighed in a vacuum.

It also goes without saying that you must always weigh things at the same location on the Earth’s surface. The acceleration due to gravity varies enormously from one place to another. To misquote Archimedes “Give me a balance beam long enough and a fulcrum on which to place it, and I shall” make a 10 kg mass weigh 1 kg.

I thing DV’s buoyant weight calculation for the feathers is way out.

DV has it right.

It’s counterintuitive. But feathes fall slowly in air becase of the large surface area not becuase of a low density.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

9.9985 vs 9.9915, yes. How accurate is your “balance beam”?

It goes without saying that atomic masses of the elements are always weighed in a vacuum.

It also goes without saying that you must always weigh things at the same location on the Earth’s surface. The acceleration due to gravity varies enormously from one place to another. To misquote Archimedes “Give me a balance beam long enough and a fulcrum on which to place it, and I shall” make a 10 kg mass weigh 1 kg.

I thing DV’s buoyant weight calculation for the feathers is way out.

DV has it right.

It’s counterintuitive. But feathes fall slowly in air becase of the large surface area not becuase of a low density.

So you think the large volume of air inside feathers has no effect on their density?

How does that work?

The Rev Dodgson said:

mollwollfumble said:

The Rev Dodgson said:

I thing DV’s buoyant weight calculation for the feathers is way out.

DV has it right.

It’s counterintuitive. But feathes fall slowly in air becase of the large surface area not becuase of a low density.

So you think the large volume of air inside feathers has no effect on their density?

How does that work?

I guess it would also depend on what you categorise as a solid. An example being aerogels
They are often treated as a solid object but nearly all of the structure is empty, hence the common label of “the lightest solid”. I don’t completely agree with that.

Spiny Norman said:

The Rev Dodgson said:

mollwollfumble said:

DV has it right.

It’s counterintuitive. But feathes fall slowly in air becase of the large surface area not becuase of a low density.

So you think the large volume of air inside feathers has no effect on their density?

How does that work?

I guess it would also depend on what you categorise as a solid. An example being aerogels
They are often treated as a solid object but nearly all of the structure is empty, hence the common label of “the lightest solid”. I don’t completely agree with that.

It doesn’t matter how you categorize it. It matters how much air the feathers displace when you weigh them in air.

The Rev Dodgson said:

Spiny Norman said:

The Rev Dodgson said:

So you think the large volume of air inside feathers has no effect on their density?

How does that work?

I guess it would also depend on what you categorise as a solid. An example being aerogels
They are often treated as a solid object but nearly all of the structure is empty, hence the common label of “the lightest solid”. I don’t completely agree with that.

It doesn’t matter how you categorize it. It matters how much air the feathers displace when you weigh them in air.

Agreed.

Spiny Norman said:

The Rev Dodgson said:

It doesn’t matter how you categorize it. It matters how much air the feathers displace when you weigh them in air.

Agreed.

No. If air is being displaced by air (at the same pressure), then the effects of the air cancel.

KJW said:

Spiny Norman said:

The Rev Dodgson said:

It doesn’t matter how you categorize it. It matters how much air the feathers displace when you weigh them in air.

Agreed.

No. If air is being displaced by air (at the same pressure), then the effects of the air cancel.

It cancels the weight of the air, but it doesn’t cancel the mass of the air.

If we are comparing the buoyant weight of equal masses of feathers (including the entrapped air) and a solid block of steel, the weight of the feathers is reduced by much more than the volume of air displaced by the keratin.

The Rev Dodgson said:

KJW said:

Spiny Norman said:

Agreed.

No. If air is being displaced by air (at the same pressure), then the effects of the air cancel.

It cancels the weight of the air, but it doesn’t cancel the mass of the air.

If we are comparing the buoyant weight of equal masses of feathers (including the entrapped air) and a solid block of steel, the weight of the feathers is reduced by much more than the volume of air displaced by the keratin.

When I was teaching laboratory work to first-year chemistry students, one of the things they found difficult to grasp was that a syringe filled with air weighs the same amount as the syringe with all the air pushed out, as well as the fully dismantled syringe.

Consider first the syringe with all the air pushed out. The total volume of air displaced is the same as the total volume of the dismantled syringe. The weight is the weight it would have in a vacuum, minus the weight that volume of air would have in a vacuum.

Now consider the syringe filled with air. The total volume of air displaced is now the total volume of the dismantled syringe, plus the volume of the air in syringe. The weight is the weight the dismantled syringe would have in a vacuum, plus the weight the air in the syringe would have in a vacuum, minus the weight the total volume of displaced air would have in a vacuum. The weight of the air in the syringe and the weight of the extra volume of air displaced due to the air in the syringe cancel.

Thus, if there is entrapped air in the feathers, then the volume of air displaced includes the entrapped air, but so does the weight of the feather, by the same amount. The entrapped air contributes nothing to the measured weight of the feather.

any normal kind of scale in a terrestrial environment

—

What is a normal kind of scale for the measurement of a large quantity of feathers?

Ian said:

any normal kind of scale in a terrestrial environment

—

What is a normal kind of scale for the measurement of a large quantity of feathers?

You could stuff them tightly together and weigh them on a cattle weigher.

So what the takeout from this is that Clive Palmer would weigh more in a vacuum.

Peak Warming Man said:

So what the takeout from this is that Clive Palmer would weigh more in a vacuum.

Not after he exploded.