So, structures that contain at least one
multi-force member, also can contain 2-force members.
The multi-force members are defined, as members that
are subjected to two, more than two forces.
And I'm going to show some pictures of those later on in the module.
And they also contain 2-force members, and
you should already know about two-force members,
because we covered that in my introduction
to engineering mechanics course, and let's go look,
go back and, and look at that that earlier course.
So, a 2-force member is a, is a weightless member again,
two frictionless pins, it can only be in tension in or compression.
And so, in this case, it's going to be in compression.
It's acting down at the top and up at the bottom 2-force
members could also be in tension, but that's all they can be.
Those equilibrium required that the forces had to be equal to each other.
They have to be in opposite direction and they have to
be co-linear, they have to be along the same line of action.
And so, we found that BY was equal to DY, they
were equal, they were in opposite
directions for equilibrium and they're co-linear.
And shape is not a factor and so, I've got several examples.
This could be a, an example of the hydraulic arm
BD, and so if I have a compression at the top and
a compression at the bottom, they can only act opposite each other.
And no matter what way I turn, the line
of action between those forces always stays the same.
Even if it was in tension, you can see that the force at the top
and the force at the bottom are equal,
opposite and along the same line of action.
And so, that's what a 2-force member is all about.
Shape's not a factor. So even if I take a curved 2-force member
like this, it can either be in compression at the ends or in tension.
Okay, along the same line of action.
And just to show that shape doesn't, isn't a factor, I've even, took a
weird S shape and again, either in tension or compression.