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Air is a gas which has various
properties which we can observe with our
senses, including the gas pressure (p),
temperature, mass, and the volume (V) which
contains the gas. Careful, scientific observation has determined that
these variables are related to one another, and the values of these
properties determine the state of the
gas.
In the mid 1600's, Robert Boyle studied the relationship between
the pressure and the volume of a confined gas held at a constant
temperature. Boyle observed that the product of the pressure and
volume are observed to be nearly constant. (The product of pressure
and volume is exactly a constant for an ideal gas.) This
relationship between pressure and volume is called Boyle's Law
in his honor. For example, suppose we have a theoretical gas confined
in a jar with a piston at the top.
The initial
state of the gas has a volume equal to 4.0 cubic meters
and the pressure is 1.0 kilopascal. With the
temperature and number of moles held constant, weights are
slowly added to the top of the piston to increase the pressure.
When the pressure is 1.33 kilopascals the volume
decreases to 3.0 cubic meters. The product of pressure and volume
remains a constant (4 x 1.0 = 3 x 1.33333 ).
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