Question

Give reason for following:
2) Sleepers are laid below the rails.
3) A gas bubble grows in size as it rises to the surface of a lake.

Answer 1

2) The pressure on a surface is reduced b distributing thrust on a larger surface area. Wide sleepers are laid down below the rail tracks so that the pressure exerted by the rails on ground becomes less.
3) At any point under the surface of liquid, pressure is proportional to its depth. As the bubble rises up, pressure of liquid surrounding it reduces which is balance by increasing its volume. (Boyl's law: PV = const).

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