Page 10 - mechanics

Chapter – 2 Concurrent forces in 2D

2.9 Free body diagram

One way to study an object is to isolate it, see how it
behaves on its own, and see how it responds to various stimuli.
These stimuli are the effects of all its surroundings.

A free body diagram is a sketch of the system (body) of
interest isolated (free) from its surroundings accompanied with
the forces that act on the system. It precisely defines the system
to which you are applying mechanics equations and the forces
to be considered. It may show one or more particles, rigid
bodies, or parts of a machine. You can draw a free body
diagram of any collection of material that you can identify. The
body in a free body diagram may be a subsystem of the overall
system of interest.

The forces are shown on the free body diagram at the points
where they are applied. These places are where you made
‘cuts’ to free the body. At places where the outside
environment causes or restricts translation of the isolated
system, a contact force is drawn on the free body diagram.
Thus, a free body diagram shows all external forces acting on
the system but shows no internal forces, i.e., forces between
objects within the body are not shown. We suggest the

62