MECHANICAL ENGINEERING DEPARTMENT
UNITED STATES NAVAL ACADEMY
24 AUG 2009
FROM: Course Director EM211
TO: Midshipmen enrolled in EM211
SUBJ: GUIDELINES FOR PRESENTATION OF FREE-BODY DIAGRAMS (FBD)
1. The following guidelines should be referenced when constructing free body diagrams
FBD in EM211 Statics.
Rule 1: Straight edges and or templates should be used to construct all FBD, associated force
vectors, and frames of reference. Numbers and letters can be drawn free hand.
Rule 2: An FBD should resemble the object under consideration in the orientation shown (i.e.,
do not represent cars, tools, beams, etc., as dots. Represent blocks on ramps as blocks on ramps).
NOT
NOT
Rule 3: Forces are placed on the FBD where they are actually applied on the object. This means
normal forces act at the surface where the force exists, not on the top. Friction acts at the surface
of the object, not at the center of mass of the object. Weight is a body force that acts over the
entire object, but is shown as a single force acting at the center of mass.
x
y
W
A
N
B
N
B
f
x
y
A
N
W
B
N
B
f
y
x
W
o
30
N
f
y
x
o
30
W
N
f
y
x
N
W
f
N
W
f
y
x
y
x
W
o
30
N
f
