Solids, Liquids & Gases: States of Matter
Pressure
Pressure is a commonly used word.
It is applied to psychological stress and mechanical
conditions. Pressure has a very specific meaning in
chemistry. It is defined as force divided by area. It may be
worthwhile to recall that a force is a "push" or a "pull". Pounds per square inch is a
pressure unit that literally states the definition. PSI
labels are visible on inflated objects like basket balls,
inflated boats and car tires. This unit has the qualities of
force (weight is a measure of force)in the numerator and
area, inches x inches = inches2, in the
denominator.
Atmospheric Pressure
When you stand on the floor, you
exert a force against the floor. The pressure you exert is
your body weight in pounds divided by the surface area under
your feet or shoes. In snow country you can see people wear
snow shoes. They do this to avoid sinking in the snow. This
trick spreads a person's body weight over a larger area. The
constant body weight and larger area produces a lower
pressure on the snow surface. This is another reason why
large vehicles have such big tires. The larger mass must be
distributed over more area or else the higher pressure on
the road surface would mechanically break down the
road.
Good facts know about atmospheric pressure and units.
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