Page 157 - Physics

Pressure

because of the higher blood pressure compared factors related to changes in cabin
to atmospheric pressure. It is important to note pressure and the natural responses of
that astronauts wear space suits to maintain the body. Swallowing helps equalize
this pressure. the pressure in the ears and sinuses,
preventing discomfort or pain caused
Altitude
by rapid pressure changes during
take-off and landing. Additionally, the
body continuously produces saliva,
and swallowing clears excess saliva
5.895 km
from the mouth and throat. Dry cabin
air can increase saliva production,
and swallowing also helps alleviate
the sensation of thirst and moisten
50 kPa Atmospheric pressure the throat. Nervousness, habit, and
Figure 7.24 Variation of atmospheric pressure with subconscious response to any throat
altitude along Mount Kilimanjaro discomfort also contribute to this
natural behaviour. While generally
The values of atmospheric pressure at some not a cause for concern, passengers
regions above and below sea level are shown experiencing severe discomfort should
in Table 7.1. seek assistance from fl ight attendants

Table 7.1: Variation of atmospheric pressure or healthcare professionals.
with altitude.
Atmospheric pressure kPa Example 7.7
Mount Everest summit (8 849 m) 33.7 A commercial aeroplane is cruising
Mount Kilimanjaro (5 895 m) 50 at an altitude above sea level. At
Mean sea level (0 m) 101.3 take off the plane was at a pressure
of 1 atm. What additional pressure
Dead sea (430 m below sea level) 106.7 should the cabin be pressurized to

normalize the pressure to 1 atm at
It can be generalised that atmospheric pressure this height if a pressure measuring
at any given point of constant g depends on instrument indicates a height
two factors: difference of 600 mmHg?
(i) density ρ ( ) of air; and Solution
(ii) height (h) of air column.
1 atm ! 760 mmHg
Thus, atmospheric pressure P, can also be
expressed as, P = hρg. ? ! 600 mmHg

600
Change of pressure during fl ight and landing !
of airplane 760
Passengers on aeroplanes frequently swallow ! 0.79 atm
saliva during fl ight and landing due to various

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