What’s heavier, a kilogram of steel or a kilogram of feathers?

boing
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African or European feathers?

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Identical, empty bags on the scales, but one is loosely inflated and sealed, and the other has been folded flat. Which will tip the balance more?

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Then why didn’t you mention the author of the post in the first reply? Otherwise, how would anyone know?

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I feel Karl Pilkington needs to weigh in to be sure.

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Much bigger platform for the bag, perhaps offset by the centre of mass of the bag being much closer to the fulcrum. Wait till he realizes how much fakery there is in them there scales.

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I’ve been seeing 404s intermittently for a while now. I haven’t noticed any pattern to them though. Most recently on http://boingboing.net/2016/09/14/heres-how-to-make-a-family.html

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That was the gag I learned as a child, which then led to the reverse result when you compare an ounce of feathers to an ounce of gold.

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Then why didn’t you mention the author of the post in the first reply? Otherwise, how would anyone know?

1: hit 404 on this post.
2: hit 404 on later post, also by the same author.
3: @LDoBe asked question.
4: Thought about it, and realized it had happened before.
5: Commented.

Next time around I will try to be a better “Jr. Data Collector”.

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Loosely inflated with what?

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If they used a real scale, instead of just a prop, of course they’d calibrate the balance point to account for the bigger platform. And they’d probably fill the bag on the scales so that they’d be sure of hitting the balance point exactly, which would be kind of assuming the conclusion.

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With ambient air. I’m not trying to be fancy; just imagine holding the bag open, waving it through the air, and knotting it closed, so that it isn’t taut with pressure.

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After spending some time with my young nephews, I realized the whole “the doctor is his mother” riddle is more easily solved today than 30+ years ago when I was their age. Progress!!!

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People seem to enjoy making fun of folks who get confused by this. I don’t think that’s very fair, or nice. This is a trick question, in which the wording is designed to intentionally confuse people by getting them to look at the differences between the two things rather than notice what’s the same. If this was a psychology demonstration, that’s cool. As a physics demonstration it’s pathetic.

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An empty bag and a bag filled with air would “weigh” the same. The weight of the air in the bag is that same as the air that it displaces. Unless, of course you heated the air in the bag, then it would be less dense and therefore buoyant. That is how hot air balloons work.

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I, too, felt pity for the fellow in the gray shirt. He caught himself in the mental trap of thinking “a kilogramme” mean same amount, by volume rather than by weight. A mentally quick person would have caught the mistake when the other fellow said, “They’re both a kilogramme,” but he is not quick. When shown the samples on the scale, he said, “Oh, look at the size of this, that’s cheating,” meaning he was still thinking they had to be the same volume.

As a math teacher I’ve seen people mentally stuck like this. Repeating the answer does not help. Explore the problem from another angle, such as taking the bag of feathers off the scale and putting feathers back on the scale handful by handful. Ask “How many feathers will I need to pile up to balance the scale?” Or maybe switch to a kilogram of wood or a kilogram of bulk candy.

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Which is my point. A kilo of steel weighs the same as a kilo of feathers, regardless of the air they displace, since the conditions for the weighing will be the same as for the balancing, assuming the two events are separate.

If it was the case that they put a steel weight on one side, put the bag on the other and filled it with feathers until the balance was level, then the air displacement is totally irrelevant. Take the bag away to weigh it and it will be 1 kilo. Even if the balance is a fixed prop, if the demonstrators are at all honest, then they will again be filling the bag until the scales read “1kg” before putting it on the prop.

One might, pedantically, argue the point about whether the weighed kilo of feathers is the same as 1 kilo of mass, but then one can cavil about whether to include the air in the bag or not, at which point we’ve lost track of whatever it was we were trying to demonstrate.

Actually, considering that steel exceeds the density of air by around 6000 times, and even a compacted mass of feathers squeezed until there’s no air left in them is probably several hundred times the density of air, I don’t think the sensitivity of any household scales, let alone a prop balance, is fine enough to eliminate any buoyancy effects.

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I’ve hit it twice in the last few days. No idea why, and the second tries worked.

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Spoilers!

Hmm, now I’m imagining a Doctor Who/Predestination mash-up…

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Others my nephews liked:

  1. If a plane crashes right on the US/Canada border where do they bury the survivors?

  2. If a rooster sitting on the very peak of a roof lays an egg, which way will it roll off?

  3. How can I have two coins that total 30 cents but one of them is not a nickel?

  4. Say most … say boast … say coast … say ghost … say roast … what do you put in a toaster?

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Where ever Obama’s secret death squads say to!

:wink:

/S

  1. If a rooster sitting on the very peak of a roof lays an egg, which way will it roll off?

Most people get this one wrong. They say “roosters don’t lay eggs!”, which is irrelevant because the question says “if”, so it is a hypothetical. :slight_smile:

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