Air Pressure

Air Pressure

1. Properties of air

   • density
     • amount of mass in a volume of air
       • mass/volume
     • more air molecules=higher density
       • less molecules=lower density
   • pressure
     • force pushing on a surface
     • atmosphere exerts pressure
       • air pressure=result of air column pushing on surface
         • molecules push in all directions
           • balance->doesn't crush object
     • denser air exerts more pressure

2. measuring air pressure

   • mercury barometers
     • glass tube partially filled w/ mercury
       • above space=almost vacuum
         • equal pressure: pushing on dish & column's downward pressure
           • high air pressure: tube mercury rises
           • low air pressure: tube mercury falls
       • mercury dish below
   • Aneroid barometers
     • airtight metal chamber
       • high air pressure: walls push in
         • needle moves based on wall shape
       • low air pressure:walls bulge out
   • Units of air pressure
     • inches of mercury
       • mercury volume=30 in. high
         • air pressure=30 in.
     • millibars
       • 1 inch mercury=33.87 millibars

3. Altitude+air properties

   • affecting air pressure
     • air pressure decreases as altitude increases
     • sea-level air=higher pressure(more air pushing down)
   • Affecting density
     • as altitude decreases density does too
     • gas molecules@high altitude=far apart
       • fewer oxygen molecules per breath