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Notes_06_02
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Virtual Work
Rigid bar in horizontal plane
sC
sA
A
B
C
2
FC
FA
 M on 2 about B CCW 
Newtonian
 FA s A  FCs C  0
Infinitesimal kinematically consistent displacements
A
C

FC
FA
Virtual work
FA   A  FC  C   0
 FA s A   FC sC   0
 FAs A  FCs C  0
Virtual power
FA   A   FC   C   0
t
t
FA  rA  FC  rC   0
Virtual power for ground connections is zero because the velocity is zero. Virtual power across
internal joints is zero because the force of link i on link j dotted with the velocity of the joint will
be equal and opposite to the force of link j on link i dotted with the velocity of the joint.
However virtual power across internal springs or dampers must be included.
 F  r
EXT
   M EXT  APPLIED  0
APPLIED
Notes_06_02
page 2 of 2
Virtual Work for Slider Crank
B
T12
A
2

1
 sin    

s  R sin   L sin   R 
 cos  
R = AB
L = BC
3

C
4 P
1
from Notes_03_01
T12    P  s  0
T12  
P  s PR sin   

cos 

matches Notes_06_01 for   0