Intuition problem about an accelerating barometer

[zanick]

I think it is pretty straight forward... there would be more pressure at the bottom of the elevator due to the acceleration of the elevator creating a higher pressure zone near the bottom, and the mercury (barometer liquid) would also have more effective weight, so 14.7psi (the benchmark for ambient at 29.92") would equate to a lower (position) value on the barometer. say the acceleration was double that of gravity, then 15" of mercury might equate to 14.7psi. (for example)

 

[sophiecentaur]

then 15" of mercury might equate to 14.7psi. (for example)

A shorter column of mercury could certainly do the job if the elevator is rising.
The point is that the air pressure in the elevator could balance the mercury if the elevator cab was tall enough to increase the effective weight of air inside it.
I have also considered another experiment. If a sealed piston were at the top of the cab, with neutral density (a weighted helium balloon, for instance) could also maintain the same ambient pressure as the cab went up or down. (A bit sketchy on the details though, I'm afraid.)

 

[zanick]

A shorter column of mercury could certainly do the job if the elevator is rising.
The point is that the air pressure in the elevator could balance the mercury if the elevator cab was tall enough to increase the effective weight of air inside it.
I have also considered another experiment. If a sealed piston were at the top of the cab, with neutral density (a weighted helium balloon, for instance) could also maintain the same ambient pressure as the cab went up or down. (A bit sketchy on the details though, I'm afraid.)

why would the elevators height be a factor ? elevator's are no air tight as you can feel your ears pop as you go up or down in one. the air pressure in the cab is the weight of the air above you to the edge of space. It would make no sense to seal it, and expand it to the edge of space when that is a condition you already have. ;) that's where the 14.7psi comes from. (and slightly less as you arrive at your 100th floor destination) . or do you mean , if you wanted to double the pressure in the elevator, that was sealed, it would have to be extended to space AND accelerated at 1g. vs accelerating 1g of the elevator sealed where the weight of the air would not change as much due to much less air mass to have its weigh increased causing a smaller pressure gradient rise?

 

[sophiecentaur]

why would the elevators height be a factor ? elevator's are no air tight as you can feel your ears pop as you go up or down in one. the air pressure in the cab is the weight of the air above you to the edge of space. It would make no sense to seal it, and expand it to the edge of space when that is a condition you already have. ;) that's where the 14.7psi comes from. (and slightly less as you arrive at your 100th floor destination) . or do you mean , if you wanted to double the pressure in the elevator, that was sealed, it would have to be extended to space AND accelerated at 1g. vs accelerating 1g of the elevator sealed where the weight of the air would not change as much due to much less air mass to have its weigh increased causing a smaller pressure gradient rise?

I maybe didn't describe the thought very well. It's easy to increase the 'weight' of the mercury column by accelerating it upwards. It's much harder to increase the 'weight' of the air above it. One way would be to use a very high cab, containing all the significant volume of the air above. Accelerating it upwards would increase the weights of mercury and air columns and produce the same reading for pressure. OR you could replace the 100km column of air with a piston which would produce an equivalent increase in internal pressure as the cab accelerates upwards. Both experiments are particularly 'thought-only' types and a bit futile but - hell why not?

PS it wouldn't be necessary too move far, vertically. The acceleration could be over a very small distance so the change in ambient pressure with altitude need not be relevant.