Pressure: Units
Pressure is a concept that has been a factor in people's lives and experiences for a long time. This is not a new concept. As a result there are many ways that we measure pressure numerically depending on the system of units we are used to. The units of pressure depend on the units we use to measure force and area. In this country we typically use pounds for force and square inches for area.
Pressure = Force/Area
Plugging these into the expression above this would lead to:
Pressure = pounds/(square inch) = psi
In spite of our comfort with these units all the the rest of the world uses very different units (with a couple of minor exceptions). In the International System of units we measure force in Newtons (we'll talk about this in a minute) and area in square meters (m2)
Pressure = Newtons/(m2) = Pascal (Pa)
These are the most common engineering units for pressure that you might run into.
There are two other pressure units which are both based on our experience living here on earth. It seems perfectly reasonable to use the pressure we experience from our own atmosphere to be a unit of measure as in fact it is. Not surprisingly the pressure pushing on you from all sides is known as 1 atmosphere (1 atm - not a source of cash!) which is more specifically average pressure at sea level. Atmospheric pressure plays a role in our weather and historically we measured atmospheric pressure using a barometer which indicates how much of a particular fluid the atmosphere can hold up. In particular we often use mercury (Hg) as the fluid and 1 atm will support a column of mercury 760 mm (roughly 30 inches) tall. This leads to a final unit of measurement call a torr which is equal to 1 mm of Hg.
There are many fascinating stories and 'tricks' that are based on atmospheric pressure. Not sure which ones I will share but we have lots more to talk about.
