$A$ barometer is kept in an elevator accelerating downwards with an acceleration $a$. What is the most likely pressure reading inside the elevator?

Describe the Torricelli experiment for the measurement of atmospheric pressure.

What does it mean when the height of a barometer is falling?

When an airplane flies at a higher altitude,it is not advisable to keep a fountain pen in one's pocket. Why?

As the depth increases in a vessel filled with liquid, the pressure ..........

$A$ manometer reads the pressure of a gas in an enclosure as shown in Figure $(a)$. When a pump removes some of the gas,the manometer reads as in Figure $(b)$. The liquid used in the manometers is mercury and the atmospheric pressure is $76 \; cm$ of mercury.
$(a)$ Give the absolute and gauge pressure of the gas in the enclosure for cases $(a)$ and $(b)$,in units of $cm$ of mercury.
$(b)$ How would the levels change in case $(b)$ if $13.6 \; cm$ of water (immiscible with mercury) are poured into the right limb of the manometer? (Ignore the small change in the volume of the gas).