Conceptual Models are great to use when introducing a topic. Get students interactively involved with the creation, evaluation, and refinement of conceptual models. Ask questions that guide them in the development process.
Causal Loop diagrams are a great tool for developing and understanding conceptual models and are invaluable for extending conceptual models into mathematical models.
The negative feedback loop shown causes the coffee to migrate toward room temperture.
See also Feedback Loops
System Behavior and Causal Loop Diagrams This is Chapter 1 of the on-line resource System Dynamics Methods: A Quick Introduction (more info) at Arizona State University. This reference provides a concise introduction to the utility of causal loop diagrams.