welcome to AI lectern line here we have an interesting situation we're looking at a screw a square threaded screw but here we have a situation where the way that the screw itself is sufficient to overcome the friction and the screw will actually go down on its own this is the situation when the angle fie is smaller than the angle theta the angle fie is the angle calculated from the coefficient of friction which is the angle between the normal and the what we call reactionary force the normal to the surface and the reactionary force and theta is the lead angle of the thread itself so if the angle theta is smaller than the lead angle the screw will actually slide down on its own and it will require a small amount of force to keep it from going down it's not a likely scenario unless the way the screw is very heavy and there's not a lot of friction between the thread and the object that the screw is going into so what we have then is we have the situation again where this is the thread of the screw this is the thread of the object the angle in between it's what we call the lead angle and this distance here is 2 pi R which is 1 circumference of the thread on the screw now notice if theta is the angle between the normal and the vertical call that data's lead angle and fee is smaller than that than the angle between what we call oh I'm pointing to the wrong angle here this should be the angle over here which should be pointing to this angle right here so this angle here is equal to fee minus theta that gives us this angle which is actually a negative angle when you think about it relative to the vertical so what happens then is we draw a diagram of the sum of all the forces here we have the weight of the screw here we have the reactionary force and then this is the force required to counteract the weight of the screw going down making the screw going down so in other words the way that the screw will push the screw down and the force F is required to keep the screw from going down now of course the force F is the force actually on the screw itself now the force that we apply here is for sappy which acts through a moment arm are the relationship between F and the force cause that we push physically against the handle right here notice that since R is much bigger than little R this is very large compared to the force required to actually keep the screw from moving but this is the situation that we have when the friction is so small that fee is larger than theta and that's how it's done