# AP Physics C Units 4 and 5 - Systems and Interactions

This unit is an overview of how to describe systems and their interactions.

The universe is a system which contains energy and objects, within its four-dimensional space. Within this system, objects interact and exchange energy. Force is the mechanism for these interactions and exchanges. We attempt to model systems with mathematical models, graphical models, vebal models, and some new representations, the Force (or Free-Body) diagram, and the system schema.

We will begin with a lab that gives a clear paradigm for the interaction between a small system of objects and the gravitational field of the earth. After modeling this situation, we will move on to modeling a slightly more complicated system with non-constant acceleration in lab two.

In this unit we are inspired by the work of Isaac Newton (CE 1643-1727).

In the second part of this unit, we will study forces in two dimensions, including circular motion and circular orbits. There will be two tests, one including only forces exerted in a single dimension, the second in two dimensions. We will return to a more general treatment of orbits, including elliptical orbits, in Unit 7.