Frames and Machines Lecture: How to identify two force members

Frames and Machines Lecture:
a. How to identify two force members;
Identifying two force member helps us to simplify our equations significantly. A two force member is a member with only forces at two points on the member.
If a member is a two force member, the member is either in tension or compression. And the two forces at the end of each member are collinear (along the same line of action) have the same magnitude and facing opposite directions
b. How to draw exploded free body diagrams

[@devin7551]

Thank you for this excellent video. I was struggling with exploded diagrams and 2 force members, but now they both make complete sense!

[@engineeringvision]

Great, that makes my day

[@Clipaholick]

so helpful doctor sanei!!

[@engineeringvision]

I am glad you found it helpful! Which university do you go to?

[@ghost_exe1]

At 9:06, why didn't we include Ay and Ax in the free body diagrams?

[@engineeringvision]

Great question and a common one. Because member AB is a two force member which means only two forces apply to the member, one at each end, knowing this will help us to know the direction of resultant force at A and B which would be along the member. If AB was not a two force member, we would have Ax and Ay at A and Bx and By at B. So we are reducing four unknowns to one ( F_A=F_B)