hey welcome back in this video I just want to have a quick discussion on to force members as then how that works in two frames and machines so if you if you isolate all of the members and you frame your machine and you get some member and you determine that maybe there's a pin on one end and a pin on the other end and there's no other external forces so these would just be the forces that the pins are causing on the machine or on the the member if you end up drawing them you think that this is the direction that they're in this would actually be incorrect for this member to be in static equilibrium because this force here would cause the object to have a tendency to translate it this way and this force would have would cause the object to have a tendency to translate to the right like that and together they're not exactly cancelling each other out so this object overall would have the tendency to translate basically somewhere down into the right and because it's wanting to translate we would find that this object is not in static equilibrium so this would be this would be incorrect if you had a situation like this where say we find these two forces that are the same magnitude and they're parallel and this is the way that you've drawn them on well this for us would give the object the tendency to translate it that way this one the opposite direction and if they're equal and opposite the object would not translate but these two parallel forces would create a force couple and cause this object to have the tendency to to rotate in this Tyrel in this direction or the sense and so unless there was an applied moment going the opposite direction they cancelled out that force couple then this member would not be in static equilibrium so the only thing that we're left with is if the lines of actions of the forces are in line with each other basically they pass there they're right on top of each other and that would cause if this is a straight member that would mean that this member as I've drawn it is an intention if we flip the arrows this member would be in compression but basically if these are the same magnitudes this is say maybe 10 kilonewtons and this is 10 kilonewtons then we would truly have equal and opposite forces either pushing or pulling and and this is something that's really important about two force members because we can actually know basically if you draw a line between the two points where the forces act on the object then we know the direction that both of those forces act in is just in a direction of that line either way now this holds true also for circular objects so if we let's draw a circular object maybe in black something like that and all right so we have something curved like this if we had if we had a force if we had two forces acting on this there's only one direction that they can go and it's basically in line with each other so maybe it's there's a force pushing here the other force would have to push just like that meaning that this thing isn't purely in tension or compression there will be some internal moments developing but as far as the reactions go these have to point the line of action just has to line up like this and that will simplify the problem greatly so if we have an example sort of like this where we have a force acting on an object and then a single reaction well that means that we will have some some reaction force in that X direction so maybe let's call this a X and we'll have some reaction force in the Y direction maybe a Y and if we look at this this is a pin and so basically these are just components of the entire reaction and it just has to be equal and opposite to this to prevent the object from either translating or rotating so if we were to draw the line of action from Earth if we were to connect the two points where the two forces act on the object it would just be like this right and this force basically if we don't know the angle we just know that if 10 kilonewtons we would know that this force has to act on the angle that's caused by the line that connects these two points and because this is a 3 4 5 triangle this would have to be 5 meters and if you just do the sine inverse of 3 over 5 that's going to give us it's a thirty six point eight six nine eight six nine degrees so that would mean that this is thirty six point eight six nine and this guy here would have to be thirty six point eight six nine and then we could really easily solve for what do we need to cancel out the X component of this force we would just have ax is equal to well that would just be ten that looks like sixteen ten coast thirty-six point eight six nine and that would just give us 8 kilonewtons and then if for a Y to cancel out the Y component it would just be ten sine thirty six point eight six nine and that would be that would give us six kilonewtons and again those are the components of the actual reaction force that this pin is causing and so the reaction force the total reaction force would just be this that would be RA or whatever you want to call that reaction at a and you would notice that it would be exactly in line and so that would just be equal to 10 kilonewtons or just by component again here we have eight and here we have six so if you ever see any member it doesn't have to be straight you know it could be circular it could be straight it could be an L shape or whatever it could be a big squiggle if there's just a pin at one end or something and then an applied force at the other hand where this could be a pin then this bit of information that shows us the actual direction of these forces really simplifies the problem because then we can just simply find equal and opposite sand then just go ahead solving that with really basic trigonometry so watch out for that to force members equal and opposite lines of action connect you know between those two points where the forces act and this will greatly simplify frame and machine problems for you