This document discusses four categories of equilibrium in two dimensions: 1) Collinear force systems have forces that are collinear and the free body diagram uses ΣFx=0. 2) Concurrent force systems have forces that meet at a point and the free body diagram uses ΣFx=0 and ΣFy=0. 3) Parallel force systems have parallel forces and the free body diagram uses ΣFx=0 and ΣMz=0. 4) General force systems have forces in any configuration and the free body diagram uses ΣFx=0, ΣFy=0, and ΣMz=0.

1. Categories of Equilibrium in Two Dimensions
Prof. P. Rajayogan M. Tech., MISTE., MASCE., FACCE, FIE., +91 9486026085 Email Id
rajayoganp@gmail.com
P
Rajayog
an
Digitally signed by P
Rajayogan
DN: cn=P Rajayogan,
o, ou,
email=rajayopganp@
gmail.com, c=IN
Date: 2014.09.22
19:55:45 +05'30'

2. Collinear Force System
Free-body Diagram
Fx  0
x
F1
F2
F3
Independent Equations

3. Concurrent (at a point) Force System
Free-body Diagram
Fx  0
F1
F2 F3
F4
x
y
Independent Equations
Fy  0

4. Parallel Force System
Free-body Diagram
Fx  0
F1
F2
F3
F4
Independent Equations
0
z
M 

5. Parallel Force System
Free-body Diagram
Fy  0 F4
F1
F2
F3
Independent Equations
Mz  0

6. General Force System
Free-body Diagram
F1
F2
F3
F4
x
y
M
Independent Equations Fx  0 Fy  0
0
z
M 