1. Forces and Moments MET 2214 Ok. Lets get started.
My name is Dr Simin Nasseri, a faculty member here at MET and I am going to teach this course MET ????, Course name.
Statics (MET 2214)
Prof. S. Nasseri

2. Moments and Forces
Part 5
Statics (MET 2214)
Prof. S. Nasseri

3. Equivalent system
An equivalent system is:
A system in which forces and couple moments acting on a body are simplified to a single resultant force and couple moment acting at a specified point O.
Consider the figure below in which point O is on the line of action of the force:
F is applied at A (Fig. a). It is needed to move the force F to point O (keeping the external effects on the body constant). Imagine we apply +F and –F at O (Fig. b). As +F at A and –F at O are cancelled out, hence +F is applied at O (Fig. c).
Statics (MET 2214)
Prof. S. Nasseri

4. Equivalent system
Now if point O is not on the line of action of the force:
Force F is applied at A (Fig. a) and OA does not pass through the line of action of F. It is needed to move force F to O (keeping the external effects on the body constant).
In this case: Apply +F and –F at O (Fig. b), then +F at A and –F at O create a couple moment (M = r x F). M is a free vector, so remember that it can be applied on any point P (Fig. c)
So, F is applied at O and also a moment M is produced (Fig. c).
Statics (MET 2214)
Prof. S. Nasseri

5. Example 1
The weights of the various components of the truck are shown. Replace this system of forces by an equivalent resultant force and couple moment acting at point A.
Statics (MET 2214)
Prof. S. Nasseri

6. Example 2
Replace the force and couple moment system by an equivalent force and couple moment acting at point P.
Solution:
-60cos30N
-60sin30+
(-140)N
-51.96N
-170N 73 P
Statics (MET 2214)
Prof. S. Nasseri

7. Example 2 8m P 4m P P 15m 140N P 40Nm 60cos30N 60sin30N
Moment due to horizontal component of 60N P
60sin30N 4m
Moment due to vertical component of 60N P P
140N
15m
Moment due to the force 140N
40Nm
Statics (MET 2214)
Prof. S. Nasseri

8. Example 3
Replace the two wrenches and the force, acting on the pipe assembly, by an equivalent resultant force and couple moment acting at point O.
Solution:
Statics (MET 2214)
Prof. S. Nasseri

9. Example 3
Statics (MET 2214)
Prof. S. Nasseri

10. Example 3
Statics (MET 2214)
Prof. S. Nasseri