Section 3.16 Force Analysis for Interacting Systems
Force analysis can be particularly powerful when you use it to examine interacting systems. The steps below are very similar to what you saw in
Section 3.9, but will help you account for multiple systems of interest.
Analyze and Represent: Identify all relevant systems and draw a Free-body Diagram for each.
Calculate: Is the acceleration of each system \(0 \mathrm{~m/s^2}\) (static or dynamic equilibrium) or not \(0 \mathrm{~m/s^2}\) (dynamics)? In addition to the Law of Motion, use any action/reaction pairs between the interacting systems.
Sensemake: All the sensemaking strategies you have will work, but a new strategy called Special-case Analysis (see
Section 3.10) can be especially useful.
Exercises Activities
1. A*R*C*S: Uh-Oh Dr. Paws.
In the video, a footstool is pushed across the floor so that Dr. Paws and the footstool speed up together. What is the maximum magnitude of the force the person could exert on the footstool before Dr. Paws begins sliding?
Tip.What kind of friction acts on Dr. Paws before she begins to slide?
