[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 521

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alkador:
Well the correct answer is steel, but can someone explain it from a physical point of view. The mass is the same.)

I assumed that the higher the density and height of the column, the more pressure on the walls of the vessel, by analogy to the support area.
 
Or, the more painful it is to hit your finger with a steel hammer weighing a kilo or a Styrofoam hammer with the same weight )))))
 
Pressure = Force/ Area. What are the forces acting on the objects? Back in 1.5 hours)
 

If they are both in a vacuum, the pressures are equal.

But they are not in a vacuum. You have to consider the Archimedean force because of the air. It acts upwards and is proportional to the volume of the body being pushed out and the density of the gas/liquid the body is in. In short,

Сила_Архимеда = плотность_воздуха * g * объем_тела

Since the volume of the foam parallelepiped is clearly larger, the Archimedean force on it is also larger. So the weight of the foam parallelepiped is less, i.e. the pressure on the support is less.

The steel one will push harder on the support.

P.S. By the way, you can also estimate how much less weight a foam parallelepiped has. Suffice it to consider only the Archimedean force acting on the foam, as it is about 250 times greater than the force pushing out the piece of steel.

The density of foam plastic can be taken as 30 kg/cubic meter, the density of air as 1.2 kg/cubic meter. So, the volume of the foam body is about 1/30 of a cube.

Therefore, the Archimedean force acting on the foam body is 1.2*9.8*1/30 ~ 0.392 (N), which corresponds to about 40 grams (if weighed on the Earth)! Well, that's actually quite a difference (I expected much less).

 
Mathemat did the job of explaining it for me))
 

The weight of the body is not the mass. Body weight is the force the body exerts on a support, or suspension. I weigh, for example, 70 kilograms (if I just stand on the scale). But if I step on the scale, the scale will show a weight that is much heavier than 70 kilograms. That is the mass. The mass equals the weight at the moment of application.

The question in the problem is clear: If the weight is the same and the footprint is the same, which body will exert the highest pressure?

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

 
Alexei, it's not about weight, it's about mass. I just gave the example of jumping on the scale. If another person jumps in exactly the same way instead of me and the total area of his feet is equal to mine, then no matter how much he weighs, if at the moment of landing the scale shows the same figure as mine, the pressure exerted by his kilograms on the scale will be equal to mine.
 
TheXpert:
)

Do you disagree? If so, please justify it. Because your smile has already made me doubt my conclusion and look for error in it.
 
sanyooooook:


Schematic.

We were once taught Theoretical Foundations of Electrical Engineering (TEE). There's still a little bit of knowledge left. As far as I remember at a glance, the calculation of currents is done with one of Ohm's laws. But I do not understand what it means to calculate currents by circuit conversion. Conversion into which circuit? Or in general, what kind of conversion are we talking about? Can you explain?

 
drknn:
Don't you agree?
Mass by itself does not exert pressure. It is a force that exerts pressure. With all that entails.
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