REVIEW OF STATICS
 Free Body Diagrams
 Forces and Moments
 Equivalent Systems of Forces and Equilibrium
 Analysis of Trusses
 Centroids and Centers of Gravity
 Moment of Inertia for Plane Figures
FREE BODY DIAGRAMS (FBD’s)
AS APPLIED TO
FRICTION PROBLEMS
The system of blocks shown impends in moving to the right
because of weight W. The coefficient of friction is 0.10 and the
pulleys are assumed to be frictionless.
(1) What is the tension in the 60kN block? [ans 6kN]
(2) What weight W is necessary to start? [ans 29.46 kN]
FBD’s of 60kN block
and 40 kN block
Applying equilibrium equations
on the FBD of 60kN block
Applying equilibrium equations
on the FBD of 40kN block
FORCES and MOMENTS
AND
EQUIVALENT FORCE SYSTEMS
SITUATION: The boat is to be pulled onto the shore using two ropes as shown
in the figure. Forces T and P are acting in each rope in order to develop a
resultant force F1, directed along the keel axis aa as shown. Given: θ = 40
deg, θ1 = 30 deg, F1 = 80 lb. Determine the magnitudes of
(3) force T, and
(4) force P
Solution:
 Fx =  P cos 40 + T cos 30 = 80
 Fy =  P sin 40 - T sin 30 = 0
[Ans: 3. T = 54.7 lb
4. P = 42.6 lb]
(5) SITUATION: Determine the resultant moment of the forces
shown about the corner point A. Each square is 1 foot on one
side. [ans 560.8 lb-ft clockwise]
EQUILIBRIUM
SITUATION: A 4-m bar of negligible weight rests in a horizontal position on the
smooth planes shown in the figure.
(6) Compute the reaction at point A. [21.96kN]
(7) Compute the distance x at which load T = 10 kN should be placed from point B
to keep the bar horizontal. [1.61m]
ANALYSIS OF INTERNAL
FORCES
(APPLIED TO TRUSSES)
(8) Calculate the internal force in member BC of the truss shown
by method of sections.[4.45kN]
CENTROIDS
AND
MOMENT OF INERTIA
For the inverted T section shown, Determine the
(9) location of the centroid relative to the bottom of the section. [ans3.5 in]
(10) moment of inertia of the T-section with respect to its centroidal Xo axis.
[ans 290.67 in4]