# What what will happen to the height of the Mercury column in a barometer when it is accelerated upwards?

What will happen to the height of the Mercury column of a barometer when the barometer is accelerated upwards assuming the value of g does not change with height?

I think the height will remain same because the weight of Mercury will increase just as weight of block increases in an upward accelerating lift and the pressure will also increase because the air molecules will hit the mercury surface harder

And if both the weight of mercury and air column would increase by same factor, then height of mercury column should remain same?

Am I correct?

Please correct me if I am wrong.

The acceleration increases the weight $$m(g+a)$$ of the mercury. If we take the moment when the velocity is just starting to increase from zero, not more changes but this. So the column height decreases.

With the gradual increase of velocity, there is a drag force that plays the opposite role. I expect that eventually it overcomes the initial effect of the acceleration.

• there is a drag force that plays the opposite role. What drag force are you referring to?
– Gert
Oct 24 '20 at 16:49
• The air resistance. Oct 24 '20 at 17:46
• You mean that flowing air would push down on the open mercury surface? Thereby pushing $Hg$ back up the tube?
– Gert
Oct 24 '20 at 17:57
• Yes. It is a force, and multiplied by the open surface area, means an increased pressure, bigger than the atmospheric pressure at the point. The column will raise accordingly. Oct 24 '20 at 18:15
• Ok, got it, Ta.
– Gert
Oct 24 '20 at 18:29

Accelerating upwards would initially increase the weight of the mass of the mercury causing it to lower in the tube. Changing air resistance would depend on the shape and design of the barometer. If it were accelerated upward for a large distance other factors would have to be taken into account, such as lower g from increased r from Earth, and lower air pressure from increasing altitude.