No, it is subtle. In order to get the weight the same, you would need to add a few more feathers to overcome their buoyancy. So for the same weight, in the atmosphere, the feathers require more mass than the lump of lead. Whereas in a vacuum, you don’t need the extra feathers.
Okay, I see what he’s saying now. Yes, he’s correct.
Actually, no. They are the Pyramids of Giza. The Great Pyramid of Giza (or Cheops or Khufu) is the largest and oldest of the three.
Hey, look at me contributing to a sciency-type thread!
An extreme example of weight and mass not being proportional in Earth’s atmosphere is a hot-air balloon.
As you add heat to an inflated balloon, mass decreases slightly (fuel is burned; the air in the envelope grows hotter and thus less dense). But weight - what a scale under the balloon would indicate - decreases significantly. Eventually, it becomes zero and even negative - the balloon rises.
The result is an object with a great deal of mass (in the case of a largeish balloon, it could easily exceed 10 tonnes) and no weight.
This topic will have the same problem all of these discussions do, random use of inconsistant definitions.
In the “metric” system the word weight has a specific defined meaning that most people ignore, and as a low precision measurement is just invalid in the cases of a large amount of buoyancy as mentioned above…
https://www1.bipm.org/en/CGPM/db/3/2/
If you choose another definition for weight no comparisons will hold except for those that choose the same definition you.
The same problem presents itself with mass.
If you use the definition of “mass” that is used by modern science you will be talking about “inertial mass” which is a measurement of a closed systems resistance to changes in momentum. Or phrased slightly differently the property that is the inertial resistance to acceleration of a body when responding to all types of force.
If you choose another definition for mass your results will vary.
In low precision uses you can use “mass” as a quantity, like cooking with divisions of the kilogram. But that is a low precision measurement that ignores that added energy like heat or changes in configuration (density) will impact the inertial properties if you have accurate enough instruments.
Stick with the Metric definition of weight and the rest mass or inertial mass and you will be OK.
Otherwise this problem will have no answers or may lead to false understanding of fundamental physics.
I worked in weights and metrology and have had to explain the difference between weight and mass many times. Here’s what gets most folks over the speedbump:
Weight is a special name for the force that results from gravity’s influence on mass.
Buoyancy is irrelevant to both mass and weight. The only relevance of buoyancy to the feathers-and-lead example is that most typical scales will be slightly inaccurate at measuring the feathers’ weight (actually they’ll be slightly inaccurate for the lead, too, but more so for the feathers).
For comparison, suppose that you’re weighing yourself on your bathroom scale, but while you’re doing so, you lean against the sink. That’ll make the scale show a lower number. Does that mean that, by leaning against the sink, you’ve lost weight? No, it just means that the scale isn’t measuring all of your weight, because part of your weight is supported by the sink instead of by the scale. Buoyancy is the same deal, except there you’re leaning against the air.
A one kilogram mass weighs 2.205 pounds on earth.
On the moon it now weighs about 6 ounces, but the mass is still one kilogram.
That’s a fantastic explanation. It also makes the point that your true weight isn’t what shows on a scale – which might not matter in everyday life but does in science.
I’d say you can’t have weight without weighing (the act of determining weight) and, since buoyancy plays a role in weighing, it’s not quite right to say irrelevant.
It’s like that old saying ‘Falls from height never killed anyone, it’s the landing.’ I argue that the landing is part of the fall, just as weighing is the only way to determine weight and buoyancy must be considered.
What you are mentioning is the operational definition of weight or the force measured by the operation of weighing it, which is the force it exerts on its support.
As the operational definition does not explicitly exclude the effects of buoyancy and it counter to the gravitational definition and will also have to take centrifugal force into account when working with scales.
So remember to discard this version when you try to use scientific formula. As example, an object in free, e.g. an astronaut does not lose “gravitational weight” during free-fall but would under the operational model.
Really this is only a pain because Newtonian and Galilean Mechanics uses a space that looks simple yet ends up being an ℝ[sup]3[/sup] bundle over ℝ[sup]1[/sup] with an inability to invert matrix that is degenerate. Note that technically under the operational definition weight needs to be a vector too.
IMHO taking the official Metric definition stand for low precision measurements and ignoring the entire concept is probably the best. As these threads show it is impossible to get people to stick to one definition for ‘weight’, mostly because people seem to want gravitational and inertial acceleration to be from separate fundamental properties when they are not, because we historically lie to students and tell them this is.
So why do they droop unequally?
mmm
Err, hate to break it to you, but no, the referent here *is *to the Great Pyramid, alone, as a unit of measure.
Darren Garrison said “Great Pyramid of Gizas.” You corrected him and said “Great Pyramids of Giza.” Chefguy in turn corrected you. There are the Pyramids of Giza and the Great Pyramid of Giza.
Sure, a typical scale will not account for buoyancy, when measuring weight. But that’s easy enough to fix: Just put the scale (and whatever you’re weighing on it) in a vacuum chamber. If only all sources of inaccuracy in measuring instruments were so easily fixed.
But using the Great Pyramid as a unit of measure, results in multiples of it. Something with 5 times the mass of the Great Pyramid of Giza is equal to “5 Great Pyramids of Giza” not “5 Great Pyramid of Gizas”. We’re nitpicking grammar here, not math or geography.
Doh! :smack: That’s twice now I’ve misinterpreted a poster in this thread.
After I build an even more impressive pyramid in Giza, there is going to be a lot of confusion in the literature. I understand something of this nature occurred when the old prototype kilogram lost mass, even though at the time by definition it couldn’t.
The question of whether a balance can be used under vacuum would come up from time to time. Few of the off the shelf instruments can be used in a vacuum, mostly because of the liquid crystal or vacuum florescent displays as well as the electrolytic capacitors. Heat dissipation was also cited. It’s possible to separate the mechanical portion of the balance from the electronics but that requires either major surgery on the scale or a very expensive specialty device and most people found another way around it.
A tangent question:
Isn’t mass, fundamentally, a function of the number of neutrons + protons (and if there’s enough of them, electrons?) in a given hunk of something? I guess that just pushes the question back a step, though – what is mass at the level of a subatomic particle?