Which is heavier; a kilogram of lead, or a kilogram of aluminium? Assume normal atmospheric conditions on planet earth.
I've asked this question to a few of my friends and one co-worker, and as soon as I suggest that kilograms is not a measure of weight, their capacity for arguing seems to dissipate into thin air. The typical answer is "a kg is a kg, they are the weight".
Apart from a lack of social skills, am I an idiot for believing that the lead is heavier?
Pretty much. This depends on the mass-density-volume relationship. Lead is a denser material, so for equal masses of lead and aluminum, the lead will occupy less volume. They have the same mass, though, and therefore require the same force to move (barring effects of increased drag due to greater volume, friction, etc).
Depends on how you measure it
On a scale in a room filled with air a kg of lead will apply a slightly higher force, as it displaces less air. Then again, that will be a tiny difference, and if you measured to that precision you'd be measuring in a vacuum anyways.
Think about this: If you measured underwater, which would be heavier? The lead clearly. Then again, if you wanted to weigh them to abotain mass, you would use a space that has been emptied of water. Same in our atmosphere
It's really more of a gotcha question than anything of actual interest
1 kg is a kg, if you multiply it with the graviation on earth you got the same 9.81N for each of them. But, lead has a higher specific density than aluminium, that meand more static energy is concentrated to the same volume as aluminium. if you look at ther molecular weight or better their atomic weight you can also see that Lead is 7.7 times heavier than Aluminium. But at the end 1 kg is 1 kg and has the same force on earth (even 7,7 times more Aluminium atoms are needed for that).
Mass in my understanding is a measurement of the amount of matter in an object. This directly corresponds to weight. Weight is a measurement of gravities effect on an object, the pound used in American imperial measurement is a measurement of weight but it's described as a certain percentage of one kilogram anyway.
Weight=mass times g
Since the mass is the same, the weight is equal too.
>am I an idiot for believing that the lead is heavier?
Yes.
Their newton weight could be possibly different from the different shapes due to how 'g' varies by elevation on earth. The 1kg AL would occupy more volume right? If this volume had a different distribution in the height direction the pull of gravity would have changed by an incalculable amount over the additional height. But the reverse could be true also with the Pb shaped to be taller. You're still a faggot for making this thread though.
Kilogram is the SI unit of mass, and mass corresponds to weight, so yes you are an idiot
Am I then mistaken in thinking that buoyancy from the air (no matter how small) would be a greater force on the aluminium, and that it acts in the opposite direction of the force of gravity, making the less dense material "lighter" - akin to how a kg of helium would not only be weightless, but also provide lift?
Yes, you are mistaken. The lower density of the aluminium means it will fall ever-so-slightly slower in an atmosphere because of increased drag resistance, but when laying idle on the ground this does not play a role. The weight --which is just mass times the gravity constant-- is exactly the same.
Kilogram of lead weighs more because it's denser and thus less buoyant
...
I get your point
But assuming the 1kg objects are placed on the floor, there is no buoyancy since solids dont produce it.
Even if buoyancy, or any other opposing force is involved, it wouldnt change the weight since
Weight = Mass * g
It might be aluminum.
Aluminum is less dense than lead. thus, it is slightly more buoyant in the atmosphere than lead. Because of this, aluminum is slightly lighter despite having the same mass as lead.
>there is no buoyancy since solids dont produce it.
Why does ice float then
But.... Lead is heavier than aluminium
Weight is not really a scientific term. You'd be better off working with the definition of mass, which is strictly just a measurement of how force is related to acceleration.
What definition is being used for 'weight'?
How are the 1kg masses created?
What are the size/shape of the masses?
The OP question is not that much different than the feather vs gold weight trap.
That limmy?
Kilograms are not a measurement of weight they are a measurement of mass wtf has happened to this board?
>Why does ice float then
Because it's in a liquid....
How much does a gallon weigh?
what the fuck?
If one or the other is heavier than they aren't really both 1kg though are they
But gas and liquid are both fluids. The buoyant force only specifies a fluid, which air is. Balloons wouldnt float otherwise..
Yes OP
This is ABSOLUTELY correct.
The bouyant force sure does apply to any object in a fluid whether it is in motion or not.
Not quite. Weight is the force due to gravity yes, but that is only the true weight assuming that no other forces are at play other than gravity. The buoyant force is at play here.
Did the math real quick, and had to use like 4 sig figs just to get a difference but...
1kg of lead weighs 9.806 N
1kg of aluminum weighs 9.802 N
So you're even though the difference is sincerely negligible (on the order of millinewtons), it is still there. Also if they were weighed in a vacuum then they would have the same apparent weight.
brainlet go bck to wherever you have came from
OP here, thanks for feedback
I've been thinking about the problem and the words we use, and now my current opinion is that "weight" is an intuitive term for everyday use; without any real meaning unless defined.
If we define weight as a net force of gravity times mass (F=gm) then both are, of course, equally heavy. - even if the question is phrased like "which is heavier; a kg of gold, or a kilogram of helium-filled-baloon-flying-away-up-there".
If we define weight as the net force in the same direction as gravity, the less voluminous (denser) object of equal mass is of course heavier, as in exerting a greater net force "downwards", due to generating less buoyancy.
When asking this question to anyone why might be offended by being told "you're wrong"; I carefully worded my questions in lines like "what is kg a measure of?", "so mass and weight is the same thing?". That my friends without any education beyond high school didn't know the difference is fine, for the matter is a trivial one. But I was concerned when to people with a bachelor (technical education with math and physics) and a master student (media/politics) was not really aware that mass and weight are not the same.
So again, thanks for the replies. The term weight lacks a good definition, so I won't ask this question again with the same confidence as I have done until now.
I dropped feathers as the comparison, because a particulary stubborn friend (bless him, a joy to argue with) made me realize I know nothing of feathers except that they grow on birds.
It certainly is a "gotcha" question, so I felt beyond smart as I was lying in bed and this meaningless question popped into my mind where the wrongness of claiming equal weight was found. My entire life almost, I would automatically have answered "the same weight".
>brainlet threads
>term weight lacks good definition
>i found out this asking chinks on a imageboard
keep deluding yourself cuck
autism: the post
>mfw I'm reading American engineering papers and they use lbf and kips as a measure of force
Is this a troll? Surely a troll would aim to waste less time than the people they are trolling.
I come back to Veeky Forums after a break of like a year to this
I missed you guys :')
ITT: OP has fallen for the oldest trick in the book and now wants to justify his delusion.
you are stupid and lack rhetorical logic, accept defeat and move on.
The thing is, hes correct
1kg of lead is heavier and I can prove it.
Assuming their centers of gravity are the same distance from that of the Earth, the respective forces of gravity on both masses will be identical, and so they're weights will be identical.
you sound like a lot of fun at parties...
Here. For the same base shape, the one with more density has lower center of gravity and is therefore acted stronglier by gravity.
>stronglier
the term is 'more bigly'
I actually googled it when I was typing and it appeared in a dictionary.
This is why Veeky Forums is a shitty board.
If they have the same mass, and the gravitational field strength which acts upon them is the same, then their weights must be the same.
Weight is just the name given to the force created by gravity, nothing else
resultant force /= weight,
weight is only from gravity, and is only one component of the resultant force
Depends on the shape of the kilogram. If the center of mass is higher above the earth, the pull of gravity is slightly less.
Well, they're busy banging on about bouyancy but if you wanted to look for a few forgotten decimals likely below current observational thresholds - and granting that both weights had exactly the same shape - the aluminium weight would have a higher center of mass, and so would have less of a field acting on it, so making it weigh less than the lead one. But not by very much at all.