Proportionalities:

            Mathematically, two variables are said to be proportional if there is a constant ratio between them.

            Directly proportional:  When both variables change in the same direction

                        Ex.  The more I eat, the more I weigh.  The less I eat, the less I weigh.

            Indirectly or inversely proportional:  When one variable changes in the opposite direction of the other.

                        Ex.  The more I exercise, the less I weigh.

Proportionalities and the Gas Laws:

            Ideal gases follow these trends:

1.  Volume is directly proportional to amount.
2. Volume is directly proportional to absolute temperature.
3. Volume is inversely proportional to pressure.
4. Equal volumes of all gases at the same temperature and pressure contain the same number of moles.

From these trends we derive the gas laws!