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A satellite revolves around the earth. Air pressure inside the satellite is maintained at 76 cm of Hg. What will be the height of mercury column in a barometer tube 1m long placed in the satellite. I think it should be the same 76 cm. Can the rotation of the satellite affect the air pressure inside the room?

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closed as off-topic by tpg2114, Jon Custer, user36790, John Rennie, heather Dec 19 '16 at 12:34

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  • $\begingroup$ Think about the effect of weightlessness on the mercury column barometer. $\endgroup$ – Farcher Dec 19 '16 at 1:01
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It would not be the same 76 cm, because a satellite in orbit is in free fall. So the mercury in the barometer will behave as if it is weightless. All the weight of the mercury is essentially "used up" in maintaining centripetal acceleration in the circular orbit. If, as usual, the tubing above the mercury is initially under vacuum, the mercury will be driven by the outside pressure all the way to the full length of the tubing, which is greater than 76 cm.

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  • $\begingroup$ Do you mean that mg( weight of mercury will be used to balance the pseudo force ( centrifugal force) ? $\endgroup$ – AScientist Dec 19 '16 at 1:03
  • $\begingroup$ Yes. That's one way of looking at it. $\endgroup$ – Chet Miller Dec 19 '16 at 1:10
  • $\begingroup$ Why would the weight of the mercury 'prefer' to be used as the centripetal force? Why won't it just resist the pressure of air? $\endgroup$ – Mockingbird Dec 19 '16 at 13:42
  • $\begingroup$ The mercury is accelerating downward toward the earth by virtue of the circular orbit. It is always falling toward the earth, but the earth is curving away, so the orbit works out geometrically to be circular. Otherwise, the mercury would travel in a straight line through the wall of the satellite (tangent to the orbit), while the satellite travels in its circular path. $\endgroup$ – Chet Miller Dec 19 '16 at 14:31
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If the pressure inside is maintained to standard 1 atm by means of suppose a heavy gas, then it would mean that when the satellite revolves the entire satellite system is under free fall, all the gas atoms ,the barometer tube ,the mercury in it ,all are under free fall . Thus in such a situation the gas atoms won't produce any pressure and if there is no pressure to be balanced then I think that the mercury in the tube won't rise.

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