Chapter 5: Gases Section 5.2: Pressure Sunday, October 19, 2014 12:43 PM Pressure = Force / Area ? **note: atmospheric pressure is caused by the weight of air molecules as they are attracted by gravity (hence why pressure decreases as altitude decreases) ? Measuring Pressure ? Barometer - device that measures atmospheric pressure Long tube filled with mercury, essentially you pour the mercury out of the tube until it stops because the mercury creates a seal and a vacuum in the closed end of the tube -pressure decreases cause the mercury seal to fall lower -pressure increases cause the mercury seal to fall higher ? Units of Pressure ? Pascal - (Pa) unit for pressure, equal to one Newton / meter squared --> Force / area