text: Charles law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles law is:
  This relationship of direct proportion can be written as:
  So this means:
  where:
  * is the volume of the gas,
  * is the temperature of the gas (measured in kelvins), and
  * is a non-zero constant.
  This law describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the law can be written as:
  The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion.