Physics
In a railway track, two rails are joined end to end with a gap in between them because

Steel can be saved
Air-gaps are necessary for bearing the weight of running train
Accidents due to expansion in summer can be avoided
Accidents due to contraction in winter can be avoided

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Physics
Inside an aeroplane, flying at a high altitude,

the pressure is the same as that outside.
normal atmospheric pressure is maintained by the use of air pumps.
normal humidity and partial vacuum are maintained.
the pressure inside is less than the pressure outside.

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