What is perhaps most important for us in the ideal gas law is that
the product of pressure times volume, pV is
proportional to T. This relation allows us to use a gas as a
thermometer in a constant volume gas thermometer.
The fact that all gases have pV heading to zero at the same temperature leads to a really physical temperature scale based on absolute zero, the temperature at which the pressure of an ideal gas would drop to zero. This is called the Kelvin temperature scale.
These things are not called "degrees Kelvin", they are called "Kelvins".
The figure on this page shows the linear relationship between pressure and temperature for two different amounts of gases that are confined to fixed volumes. The slope of the curves depend on the number of moles and the volume, but for all cases on finds that the resulting (extrapolated) straight lines intersect at a temperature of -273.15°C for 0 pressure.
[The reason that the lines need to be extrapolated to 0 pressure is that gases do not remain gases all the way down to these very low temperatures, but instead turn into liquids and even solids. If you want to remind yourself of the temperatures at which this happens, you may want to play with the phase transition temperature applet again.]
© MultiMedia Physics, 1999