of this slide is also available.
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
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.
In a scientific manner, we can fix any two of the four primary
properties and study the nature of the relationship between the other
two by varying one and observing the variation of the other. This
slide shows a schematic "gas lab"
in which we can illustrate the variation of the various properties.
In the lab a theoretical gas is confined in a blue container. The
volume of the gas is shown in yellow and is determined by the
position of a red piston. The volume can be changed by moving the red
piston using the red screw at the top of the piston. The number of
moles of the gas is indicated by the number of small black
"molecules" in the volume. The moles can be changed by injecting or
withdrawing molecules using the pump at the left.
The pressure can be changed by adding
or removing green weights from the top of the red piston, and the
temperature can be changed by heating the container with the "torch"
at the bottom.
There are two
probes inserted into the bottom of the container to measure the
pressure and the temperature on the two gages.
As the green weights are added to the top of the piston, the pressure inside
the vessel increases and the volume decreases. The relationship is plotted on
the graph at the right.
- Re-Living the Wright Way
- Beginner's Guide to Aeronautics
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