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[dree12]

From http://www.bay12forums.com/smf/index.php?topic=96724.0:

While many people have complained that weight is the measure of the "force of gravity", to the common person this is a ridiculous definition. What this would imply is that a kilogram of ballooned nitrogen would weigh the same as a kilogram of uranium. In that thread, I posted the more generally accepted equation of weight, given below:

weight (n) = mass (kg) * magnitude (m/s²) - air density (kg/m³) * volume (m³) * magnitude (m/s²)

This has received support from one of the definitions posted by Cruxador, and opposition from most of the others:

For weight:
Google: A body's relative mass or the quantity of matter contained by it, giving rise to a downward force; the heaviness of a person or thing.
Dictionary.com: the force that gravitation exerts upon a body, equal to the mass of the body times the local acceleration of gravity: commonly taken, in a region of constant gravitational acceleration, as a measure of mass.
TheFreeDictionary.com: The force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity.
Wikipedia: In science and engineering, the weight of an object is the force on the object due to gravity.
Merriam-Webster: the force with which a body is attracted toward the earth or a celestial body by gravitation and which is equal to the product of the mass and the local gravitational acceleration

(bold: support common sense definition; italic: oppose common sense definition; no formatting: neutral)

This suggests that what humans generally think of weight (the Google definition) is the heaviness of an object or the force needed to hold it up. However, scientifically it seems most scientists tend to define it as the weight without buoyancy, or simply the force of gravity. This leads to confusing and unexpected results like a massive helium balloon weighing the same as an uranium pill of the same mass.

Weight has nothing to do with air resistance, however. An object at rest encounters no air resistance, rather it encounters fluid buoyancy (no, these are not the same thing). If weight is measured in the "common sense" model, it would make sense that a kilogram of feathers weighs less than a kilogram of gold.

The term "common sense" is likely to spark debate among the scientists in this community. Most people would not accept that nitrogen would weigh the same as uranium on Earth. The reason for this is that there is no other practical application for something's weight, rather than the force needed to keep it at rest on Earth, where an atmosphere is already providing some counterforce. So, the "common sense" definition of weight is "the force needed to keep a resting object at rest" or "the force a solid ground exerts on an object of relatively miniscule mass to keep the object at rest", not "the force of gravity on an object".

If you have any disagreeances with this post, please share them below.

[Pnx]

In general I tend to go with the scientific definitions for these things, so for me weight equals mass * force of gravity. This actually strikes me as the common sense one too, I've never actually heard of a balloon having a negative weight... Well outside of computer simulations where there is no actual buoyancy so it's fudged.

[Criptfeind]

to the common person this is a ridiculous definition. What this would imply is that a kilogram of ballooned nitrogen would weigh the same as a kilogram of uranium.

I don't know anyone who thinks that is ridiculous that a large amount of a miniscule weight thing is the same as a miniscule amount of a large weight thing.

I mean seriously. Balloons are lighter then air, which is why it floats. Lighter implies it still has a weight.

Can you please point me to these "common people"?

[dree12]

to the common person this is a ridiculous definition. What this would imply is that a kilogram of ballooned nitrogen would weigh the same as a kilogram of uranium.

I don't know anyone who thinks that is ridiculous that a large amount of a miniscule weight thing is the same as a miniscule amount of a large weight thing.

I mean seriously. Balloons are lighter then air, which is why it floats. Lighter implies it still has a weight.

Can you please point me to these "common people"?

When you want to lift X newtons of weight, and I give you a helium balloon, are you actually lifting X newtons?

In general I tend to go with the scientific definitions for these things, so for me weight equals mass * force of gravity. This actually strikes me as the common sense one too, I've never actually heard of a balloon having a negative weight... Well outside of computer simulations where there is no actual buoyancy so it's fudged.

My opinion is that if it is an unavoidable force at rest, then it is a part of weight. If I weigh 200N and carry a balloon, do I weigh more or less? I personally think I weigh less.

[Heron TSG]

When you want to lift X newtons of weight, and I give you a helium balloon, are you actually lifting X newtons?

Yes, but it rises faster than usual due to the laws of buoyancy.

[Criptfeind]

Damn it man.

Does anyone else want to slap this guy? No offense to you. But this is not something you can have as a opinion.

When you want to lift X newtons of weight, and I give you a helium balloon, are you actually lifting X newtons?

You can't lift a newton. Newton is not the same word as unit. And if you did use units then the answer would be: NO. I am not lifting shit. The air is lifting it.

[dree12]

When you want to lift X newtons of weight, and I give you a helium balloon, are you actually lifting X newtons?

Yes, but it rises faster than usual due to the laws of buoyancy.

My point is that the counterforce you use is negative, so you aren't lifting anything at all.

[Heron TSG]

Have you taken Physics, man? In Washington (State), at least, high school students are required to take Physics. This isn't something the 'common man' doesn't know.

My point is that the counterforce you use is negative, so you aren't lifting anything at all.

Only because the air is already lifting it. If you jump up and keep pushing, it does go faster. You can lift a helium balloon, and it does take force.

[Criptfeind]

Edit: Whoops deleted this post sorry.

Spoiler: Here. This should cover it. (click to show/hide)

[dree12]

The counterforce is not negative. You can't exert a negative force. You are exerting a positive force in the opposite direction that the air is exerting on the balloon

You know what I meant. No need to get pushy over terminology.

Have you taken Physics, man? In Washington (State), at least, high school students are required to take Physics. This isn't something the 'common man' doesn't know.

My point is that the counterforce you use is negative, so you aren't lifting anything at all.

Only because the air is already lifting it. If you jump up and keep pushing, it does go faster. You can lift a helium balloon, and it does take force.

Maybe lifting was a bad word. I meant something more like "keeping at rest", or reducing accelleration to zero. And I have a fairly good grasp on physics - otherwise I wouldn't be able to come up with the revised weight formula.

I think this is getting too linguistic and unphysical. I prefer to use "force of gravity" to refer to what you all call weight, and weight to refer to "downwards force at rest". This during normal speech, because it makes sense this way. Not on a physics test, of course.

(to be honest, physics tests refer to "force of gravity" as well...)

[Criptfeind]

You know what I meant. No need to get pushy over terminology.

No. I don't know what you meant. You said the point was you were exerting a negative force. Your whole point is the force is negative yes? Which is untrue.

Maybe lifting was a bad word. I meant something more like "keeping at rest", or reducing accelleration to zero.

How is that a improvement? If that is what you mean then you must have said:

My point is that the counterforce you use is negative, so you aren't keeping at rest/reducing acceleration to zero anything at all.

Which is untrue I assure you. Please go let a balloon go and see if it does nothing.

[webber]

What the hell.

Weight: m*g, where m - mass of our object, g - gravitational acceleration constant for particular celestial body.

The balloon floats in atmosphere because of Archimedes force. Put it into a vacuum chamber, and you will have to lift it manually, if you want to.

[Criptfeind]

What the hell.

I know roight?

I had no idea this was even a issue for anyone.

[dree12]

My point is that the counterforce you use is negative, so you aren't keeping at rest/reducing acceleration to zero anything at all.

Which is untrue I assure you. Please go let a balloon go and see if it does nothing.

Thank you, this is what I meant. But I assure you it is perfectly true. If it is confusing, a negative counterforce (or, as you will a positive downwards force) is needed to keep the balloon at rest. This means the downwards force (or common usage of "weight") is negative.

What the hell.

Weight: m*g, where m - mass of our object, g - gravitational acceleration constant for particular celestial body.

The balloon floats in atmosphere because of Archimedes force. Put it into a vacuum chamber, and you will have to lift it manually, if you want to.

I meant on Earth, weight should include buoyancy.

What the hell.

I know roight?
I had no idea this was even a issue for anyone.

I understand that nobody who has posted here shares my opinion, and I assume that is a characteristic of the bay12 community. I do have difficulty explaining every concept here to people, though - my explanation skills are rather lacking. But I guarentee I am not the only one who has this opinion - which is opinionable as it is a matter of differing definitions.

[alway]

Your false definition also incorrectly assumes air has a single density. The density of air changes based on temperature (Boyle's Law), different chemical compositions, ect. And of course it invalidates the concept of weight for any environment other than the surface of Earth. For it to apply to places like Jupiter, under your false definition, some arbitrary value would need to be chosen to distinguish what is 'air' and what is considered the liquid surface (Jupiter is essentially a cloudy planet which as you go deeper becomes more and more viscous, likely with no clear denotation between liquid and gas). In order for it to work with Jupiter and similar planets, your definition would need to be revised from atmospheric density to 'whatever density it is surrounded by,' and even that is a highly nebulous and almost as worthless definition.

Thus weight is measured in a vacuum.