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What is atmospheric pressure and do you measure it?

The earth's atmosphere is made up of nitrogen, oxygen, argon, carbon dioxide and traces of other gases.

Although you don't really feel it, air exerts a pressure on everything.

Each molecule of air exerts a pressure when it collides on its surrounding.

How do you measure atmospheric pressure?

A barometer is used.

Evangelista Torricelli invented the first barometer, known as the Torricelli's tube.


  • Fill a container with mercury
  • Fill a test tube with mercury
  • Invert the test tube
  • Lower into the container
  • The mercury column drops
  • A vacuum is created
  • The atmosphere exerts a pressure preventing the column of mercury from dropping all the way.
  • The downward pressure from the mercury column and the atmospheric pressure will reach equilibrium.
  • Under normal atmospheric pressure at sea level, the column of mercury = 760mm
  • At higher altitude, atmospheric pressure reduces.
  • How to calculate atmospheric pressure?
  • Based on the column of mercury, pressure = height x density x gravity
  • Pressure = 0.760m x 13.596 kg/m^3 x 9.8 m/s^2 = 1.01325 x 10^5 Pa
  • 1 bar = 10^5 Pa
  • Pressure = 1.01325 Bar
  • 1 atmospheric pressure (ATM) is defined as
  • 1.01325 Bar
  • 101325 Pa
  • 760 mmHG
  • 760 TORR
    Atmospheric pressure and mercury barometer