There are, again, two videos in this lesson, and there is also this INTERACTIVE FIGURE to help you with the concept. Don't forget the quiz!
Source: Hewitt, P. G. (2015). Conceptual Physics (12th ed.). Boston, MA: Pearson.
Source: HEWITT, P. G. (2015). CONCEPTUAL PHYSICS (12TH ED.). BOSTON, MA: PEARSON.