[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 522

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TheXpert:
Mass does not exert pressure by itself. It is a force that exerts pressure. With all that entails.

Can you please show me all the implications?
 
drknn:

Body weight is not mass. Body weight is the force the body exerts on the support or the suspension. [...]

Remember, what is pressure? In a simplified version, we can say that it is the force that a body exerts on 1 square x area. Since the mass and the footprint are the same, the pressure is the same in both cases.

Everything is correct. The problem is formulated correctly. It talks exactly about a mass equal to 1 kg.

The weight of a body (in this case) is the force with which it acts on the support on which it lies. A body being weighed in a gas atmosphere has two forces acting on it, one downwards, the gravitational force, and one upwards, the Archimedean force. The gravitational force is equal for both bodies. But the Archimedean forces are different. So the weights of these bodies are different. And with the same support area, they'll be pushing on it differently.

You are saying everything correctly. I even have nothing to argue with you.

There are no jumping parallelepipeds, and there is no reason to bring them in. The bodies are lying quietly on regular shop scales (electronic, for accuracy). No wind, no vibrations and the flight is fine :)

Believe me, I remember the difference between weight and mass pretty well too.

 
Mathemat:

Believe me, I also remember the difference between weight and mass pretty well.

:) No questions for you - I'm not the one with the full baggage of knowledge - I didn't like physics at school, although, oddly enough, algebra and geometry were my favourite subjects. I just didn't understand why I needed physics.

Maths, yes, there's no getting around it, but physics and chemistry, I never understood why I needed it in my life. It was never really useful. Although I tried to understand physics (as opposed to chemistry) :)

 
Mathemat:

Everything is correct. The problem is formulated correctly. It is talking about a mass of 1 kg.

The weight of a body (in this case) is the force it exerts on the support on which it lies. A body weighed in a gas atmosphere has two forces acting on it, one downwards, gravity, and one upwards, Archimedean. The gravitational force is equal for both bodies. But the Archimedean forces are different. So the weights of these bodies are different. And with the same support area, they'll be pushing on it differently.

You're saying it correctly. I don't even have anything to argue with you about.

There are no jumping parallelepipeds, and there is no reason to bring them in. The bodies are lying quietly on ordinary shop scales (electronic, for accuracy). No wind, no vibrations either, flight is fine :)

Believe me, I remember the difference between weight and mass pretty well too.

Strictly speaking, the highlighted is incorrect. If both bodies stand on their supports, then

the correct answer is that the weight of both bodies will be the same. The presence of a side wind is not considered.

Hint: Archimedean force is a surface force.

 
VladislavVG:

Strictly speaking, the highlighted is incorrect. If both bodies stand on their supports, then

the correct answer is that the weight of both bodies will be the same. The presence of a side wind is not considered.

Hint: Archimedean force is a surface force.

That's exactly what I mean. Mass is a variable - it's like a snapshot of a camera. Static, measurable. But only at THIS moment in time! If at that moment in time , mass and floor area are equal, then pressure will also be equal.
 
drknn:
That's exactly my point. Mass is a variable - it's like a snapshot of a camera. Static, measurable. But only at THIS moment in time! If at that moment in time mass and floor area are equal, then pressure will also be equal.
Not so: if the base areas of parallelepipeds are the same, then the Archimedean force will be the same, because the Archimedean force is the result of the surface forces acting on the body from the medium, which has 1. mass, more precisely the density gradient - (at different levels density is different) 2. fluidity. if the body stands on a support, the Archimedean force is not directed upwards, since the medium does not act on the bottom - that is only presses down. If the base areas are the same, the vertical component is also the same and the horizontal component is compensated. For arbitrarily shaped bodies - this will not always be true. Yes, that being said, we assume that the density of air at the upper boundaries is the same. And, by the way, if the bodies are suspended, that's when the weight will be different and precisely because of Archimedes' force.
 
Alex, tell me, what forces at THIS moment in time can we neglect?
 
VladislavVG:
if the body is standing on a support, the Archimedean force is not directed upwards, as there is no effect on the bottom of the medium - that is, it only presses down.
Where is it directed :)
 

Uh, yo. I realise I've come to the wrong end of the conversation. Guys, kudos. You have a grasp of an area of expertise that I don't seem to know at all. It's okay - everyone's an expert in their own field. But the conversation is interesting. I will attend.

 
TheXpert:
And where it is directed :)
It's pointing towards the support. Try pressing an empty glass against the bottom of a bathtub so that no water flows under it - and see if it bursts ;).... Also see how the diving bell works ;). More precisely, this force (Archimedes) will be directed by the gravitational force acting on the fluid medium.
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