What is pressure ?
A gas pushes
upon all surfaces with which it is in contact: it is said it exerts a
What is atmospheric pressure ?
atmospheric pressure corresponds to pressure exerted by air from the
A simple experiment demonstrates the existence of atmospheric pressure:
A glass is completely filled with water. A sheet of paper is pressed
against the glass and then the glass is returned.
Water remains in the glass and doesn't flow.
Despite its weight the water is kept inside the glass because the
outside air pressure is greater.
unit of pressure is Pascal (Pa)
Is also used:
- The hectopascal (hPa) = 100 Pa 1 hPa
- The bar (bar) 1 bar = 100000 Pa
How to measure pressure ?
atmospheric pressure is measured with a barometer.
At sea level atmospheric pressure is about 101300 Pa or 1013 hPa or
about 1 bar but it may vary and leads to high pressures (anticyclone)
corresponding to areas of good weather or it can leads to low pressures
(depression) corresponding to areas of bad weather.
When a gas is enclosed its pressure is measured with a manometer.