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Well you can ask "why" to anything. Why atoms? Why gravity? they are just things we observe.

Why atoms what? The difference is that those are practically metaphysical questions (why existence?) whereas the ones I asked above are genuine bits of scientific enquiry.

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More specifically, weight is the concept we came up with when looking at the world as we encountered it, but it was realised that it was a bad or at least incomplete, concept. When we came up with concepts like inertia and momentum, mass was created as a label for the property that an object always has regardless of any forces acting on it or the way in which other objects experience it.

Precisely my point - we're teaching kids the incorrect theory before we teach them the correct one.

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Also, atoms were invented before Newton, by the ancient Greeks.

Pfft. Happy accident, and they had the details all wrong.

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But you don't really need to know about atoms first; all you need to know is that an object has a certain mass but it is experienced differently in different situations.

Why?

This is my whole problem with the thing. The experts give us this stuff as if it just exists on its own with no cause. It's hell for whoever's trying to learn it, because instead of having a logical chain of cause and effect to memorise, they've just got a bunch of random unconnected facts. If they want to know how it fits together they have to work it out themselves.

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The fact is they describe different things; you might be able to pick up a car on the moon, because it has low weight, but if you hit by one that was moving you'd still get hurt, because it still has all its mass.

And my explanation makes that perfectly clear, leaving no whys unanswered. "An object has a certain mass but it is experienced differently in different situations" (the explanation generally favoured by the textbooks) is basically saying "And it's true 'cos I say so, now shut up and learn this diagram of the nitrogen cycle".

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Originally Posted by Zichao

Why atoms what? The difference is that those are practically metaphysical questions (why existence?) whereas the ones I asked above are genuine bits of scientific enquiry.

Well them as below, your "why" question isn't specific enough to be answerable.

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Precisely my point - we're teaching kids the incorrect theory before we teach them the correct one.

Well, inasmuch as most people don;t really pay much attention to the specific difference between mass and weight, that's probably true. But that;s not the fault of science teaching.

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Pfft. Happy accident, and they had the details all wrong.

I don't think that's entirely true.

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Why?

Why what? I don;t understand what you;re asking about. If you put an object on a scale here, and on the moon, the readings would be different. That;s just an observable feature of how the physical world works.

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This is my whole problem with the thing. The experts give us this stuff as if it just exists on its own with no cause. It's hell for whoever's trying to learn it, because instead of having a logical chain of cause and effect to memorise, they've just got a bunch of random unconnected facts. If they want to know how it fits together they have to work it out themselves.

It all seems perfectly logical to me, except for the existential question of "why is reality like this". We observe things and make theories explaining them.

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And my explanation makes that perfectly clear, leaving no whys unanswered. "An object has a certain mass but it is experienced differently in different situations" (the explanation generally favoured by the textbooks) is basically saying "And it's true 'cos I say so, now shut up and learn this diagram of the nitrogen cycle".

Well no, it says it's true because it is observably so.

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Well them as below, your "why" question isn't specific enough to be answerable.

I managed to answer it in one sentence, and I'm not even an expert.

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Well, inasmuch as most people don;t really pay much attention to the specific difference between mass and weight, that's probably true. But that;s not the fault of science teaching.

Start the earliest textbooks with "everything is made up of little bits of stuff: atoms" and you've solved it.

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I don't think that's entirely true.

I do.

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Why what? I don;t understand what you;re asking about. If you put an object on a scale here, and on the moon, the readings would be different. That;s just an observable feature of how the physical world works.

And extremely unsatisfying, put like that, because you still haven't told us why.

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It all seems perfectly logical to me, except for the existential question of "why is reality like this". We observe things and make theories explaining them.

It's also a fact that it's far easier to remember "mass is all the atoms added together, and weight is how hard gravity pushes them" than "an object has a certain mass but it is experienced differently in different situations", because the people doing the learning are humans rather than computers. It might be easy for you, but the people having to learn it in schools are little kids, many of whom have no special aptitude for the subject.

It's the same mistake that the big, French daily papers make. They hire these über-intellectual journalists who can craft a technically perfect article that no one wants to read, because it's desperately boring and extremely heavy going, having been written to be read by a robot entirely unfamiliar with human society.

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Well no, it says it's true because it is observably so.

That doesn't help when you're six years-old and trying to work out how come weight apparently isn't really weight after all.

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Originally Posted by Zichao

I managed to answer it in one sentence, and I'm not even an expert.

Well so did I, you may recall.

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It's also a fact that it's far easier to remember "mass is all the atoms added together, and weight is how hard gravity pushes them"

For these purposes, it doesn't really matter what mass is made of - it could be atoms, or concentrated aether, or finely ground pixies. It doesn't really explain anything becuase all you've done is explain one object by reference to another object.

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than "an object has a certain mass but it is experienced differently in different situations",

But whatever is accelerating an object might not be gravity, it might be an electrical or magnetic field, or the force of a rocket, or the bouyancy of water or gasses.

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It might be easy for you, but the people having to learn it in schools are little kids, many of whom have no special aptitude for the subject.

Well I haven't actually proposed anywhere that we should be teaching this to six-year olds.