Make a manometer
Anti-Gravity Water 
The Cartesian Diver
The Magic Can - can joint without glue.
Air Occupies Space
Crush the can with the Power in Air Pressure
Take a syringe without needle and a beaker containing water.
put the end of the syringe inside the water and pull the plunger.then we observe that the water rises into the syringe.i.e.there is a pressure exerted inside and outside the syringe,as that pressure decreased inside the syringe when we pulled the plunger and  the pressure outside remained the same,the water was forced inn to maintain the balance.and that pressure is the pressure of atmosphere.
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