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[Criptfeind]

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.

First thing. Unless one is using a actual weight, no one calls it weight. They call it a downward force.

Second thing. No. No it is not.

There is.

No such.

Thing as.

A negative force.

It is a POSITIVE. DOWNWARD. FORCE.

Just because it is acting against another (positive!) force does not mean it is negative.

This is a fact man.

As to the truth of a earlier statement. I was joking, but now I am serious. Go let go a of a balloon and see what happens.

[dree12]

As to the truth of a earlier statement. I was joking, but now I am serious. Go let go a of a balloon and see what happens.

See what happens yourself... The balloon is held up by the buoyancy of the air, and that is greater than the gravitational force. So its "net downwards force" as you would call it is inverted and positive .

It is a POSITIVE. DOWNWARD. FORCE.

I never claimed negative forces existed. But you knew what I meant, didn't you? Forces have magnitude and direction, and when I talk about these hypothetical negative forces anyone with more than two brain cells would know that I meant inverted direction forces with the same magnitude...

Remember x + (-x) = 0? This still applies to vectors, believe it or not. v + (-v) = 0. Amazing, isn't it?

(btw, before you start complaining about my zero vector looking like a scalar - I'm too lazy to do the proper arrow)

[Criptfeind]

See what happens yourself... The balloon is held up by the buoyancy of the air, and that is greater than the gravitational force. So its "net downwards force" as you would call it is inverted and positive .

How does this have to do with any thing? You claimed that you were exerting no force at all over a balloon being held.

And by claimed I mean spewed a bunch of words you only half understood that came out to mean that.

Also I could call it a new upward force. Or something. Not a inverted downward force.

I never claimed negative forces existed.

My point is that the counterforce you use is negative

This means the downwards force (or common usage of "weight") is negative.

You are clearly a liar or very very confused.

[Heron TSG]

(╯°□°）╯︵ ┻━┻

This requires a positive upward force.

┬──┬ ノ( ゜-゜ノ)

This requires a positive downward force.

ಠ_ಠ

[Kogut]

While many people have complained that weight is the measure of the "force of gravity", to the common person this is a ridiculous definition.

Well, common person can believe that astrology/homoeopathy works and autism is caused by vaccines.

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)

[citation needed]

[Il Palazzo]

The term "common sense"

ArglebargleEinsteingrrhateblargh.

Let me just say that it makes little sense to try and write down a single definition of the common meaning of weight - it can mean different things at different moments for different people. It could be e.g.the measurement on the scales, the force needed to hold a body still against the force of gravity, mass, or the force needed to hold an object still, period. The exact meaning is context-sensitive and generally people have no problem discerning between them. For example saying that "I weigh more in an ascending elevator" makes it clear that I mean the net force acting downwards; "a baloon is lighter than air" makes it clear it's about buoyancy caused by the difference in density between the baloon and the surrounding air.

In physics the general use of weight is indeed the force acting on a body in a gravitational field: W=am, where both W and a are vectors pointing from the mass m towards the gravity source.
By convention the direction towards the source of a gravitational field is denoted as a negative vector, so anybody thinking in vectors would be required to say that weight is always negative.
However, since both vectors in the equations have the same, constant direction they can be treated as scalars. In this sense there can be no negative values of vector W, as gravity is never repulsive.

If anybody were to calculate the net force acting on body suspended over(e.g.by standing on the surface of) a planetary body such as Earth, then they'd have to take into account the gravitational field at a given distance from the centre of mass of the planet, the centrifulgal force at a given latitude, the buoyancy exerted by any fluid present(possibly of varying density), coriolis force and any other inertial forces that may apply as well as tidal forces from near celestial bodies.
One could call the result "weight", but keeping in mind it would not be the definition physics uses.

Finally, there's the definition of weight used by ISO, and that is the combination of the gravitational force and the centrifugal force.

ed: grammar

[Leafsnail]

This definition of weight is suddenly completely tied to earth's atmosphere at a certain altitude at a certain temperature at a certain pressure.  I don't see why we should do that.

Also, according to your logic... well, if I'm in a swimming pool, the water's pushing me upwards (in exactly the same way as air does).  That means I have a negative weight when I'm in a swimming pool, right?  Or is my weight still attached to the air I'm no longer in for some reason?

[Bohandas]

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"?

Seconded.

[MonkeyHead]

As others have said, wight is a contributing factor to resultant forces, not the only thing responsible for thier magnitude nor direction. OP needs Physics lessons. I would be happy to oblige, but my rates are not cheap.

Edited for clarity...

[Flying Dice]

Isn't the whole point of 'common usage' expressions that they are inaccurate and largely unrelated to what they attempt to address, and that they are based on uninformed personal opinion? That seems to preclude any sort of single definition for something that is, by its nature, incoherent and incorrect. Also, since when is this an issue for 'the common person'? Isn't at least basic physics a high school graduation requirement (here in the US, at least)? I know I'm very far from knowledgable in regards to physics (I slept through half the lectures, and it wasn't calculus-based, for some insane reason), but I still don't have this sort of, excuse the expression, idiotic misconception. If there is any sort of confusion over weight, it would seem to be more related to the traditional bit about weight as opposed to mass, which at least has some small founding in rationality because most people aren't going to need to worry about the difference between the two in the course of their lives. Anyone who would approach this as a serious concern is probably much more busy crossreferencing their horoscope and daily routine.

[EveryZig]

In its common use, wight is a measurement of how fat you are :V

Seriously, though, measuring weight by the net force after atmosphere sounds simple at first, but it eventually leads to bringing in atmospheric conditions, volume, density, shape and other stuff.

[MonkeyHead]

Doing so means you are calculating a resultant force - this isnt weight. Weight is the component of that resultant force that acts towards the centre of whatever gravitiational well you are in by virtue of having mass. Simple.