The atomic theory of matter tells us that a gas is made up of tiny particles called atoms (or molecules, which are combinations of atoms), which are constantly in motion, smashing into each other and the walls of whatever container they might be in. Here is a highly visual model of this idea.
Stages of behavior change. Transtheoretical Model of Change, a theoretical model of behavior change was originally explained by Prochaska & DiClemente, 1983. The TTM is a model of intentional change. This model focuses on the decision making of the individual. source: http://currentnursing.com/nursing_theory/transtheoretical_model.html