Demonstration of Atmospheric Pressure
(1) Collapsing can experiment
The effect of atmospheric pressure can be demonstrated by evacuating a tin using a vacuum pump. Before the air is pumped out, the pressure inside the tin is equal to the atmospheric pressure. When air is partially removed from the tin by the vacuum pump, the pressure of air inside the tin is less than the
atmospheric pressure. Hence the collapsing of the tin takes place.
(2) Megdeburg-hemisphere experiment
The very existence of atmospheric pressure was first demonstrated by a German scientist Von Guericke. His experiment is historically known as Magdeburg hemisphere experiment because it was performed first in the city of Magdeburg in Germany. He took two hollow metallic hemispheres. The hemispheres were placed in contact. The air inside the hemispheres was pumped out by a vacuum pump. After the partial removal of the air from inside the hemispheres it was almost impossible to separate them by pulling them apart. It is due to the fact that the pressure exerted by the atmosphere on the outer walls of the hemispheres is much greater than the pressure exerted by the air left inside the hemisphere.
In the original experiment with perfect vacuum inside the hemispheres, even sixteen horses (eight on each side) could not separate the hemispheres.
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