Application of Newton's Laws
Figure 3 Free-Body Diagram
The frictional force (F ) is a force that opposes the direction of motion. This force is
explained in more detail in the chapter on types of forces.
To solve this practical problem, the student would assign values for each force as determined
by data given in the problem. After assigning a sign convention (e.g., + for forces upward and
to the right, - for forces downward and to the left), the student would sum all forces to find
the net force acting on the body. Using this net force information and appropriate equations,
the student could solve for the requested unknowns. A variation would be to have the
student find an unknown force acting on the body given sufficient information about the other
forces acting on the body. The student will learn to solve specific examples using free-body
diagrams in a later chapter.
Some advanced free-body diagrams for various types of systems are shown in Figure 4.