 you determine the direction of flow? Direction of flow is to the stream line. So if I know the stream line, which stream line it is, I can just draw the tangent and I can tell you at this point the direction of flow is this. Simple, alright? Now, stream line gives you more information than just telling you about the dicey-how. For example, you should take as a first, sorry, I missed that. Suppose you have 10 intersect, reason? Suppose the intersect. So which velocity it is? A particle cannot. So if the intersect, you'll have two tangents along the two stream lines, okay? Which is, there's no unique path when it comes to the red flow. Same part, similar particle starting from here could follow a different path, okay? So there is no fixed path. The intermixing is so much, you can't determine the, so you cannot have any scientific theory as since we were discussing about laminar, so turbulence. I was talking about the information given by the stream line flow. So suppose this is a pipe, clearly this is bigger cross-section, sorry this is bigger and that is smaller and this is not the end. It is a part, fine? Don't confuse by note, okay? Now, if I draw a stream line starting from here then this will be there. Now, there are infinite particles, right? So I can density of stream line, number of streams per area is proportional to the magnitude of the, so this is what the concept that we have discussed initially. One was, okay? So let's take it one by one. First, I will apply conservation of mass. Fluid dynamics is also the equation of content with beauty mass, right? I should have started the discussion with that. How many of you, she can do it? One kg mass goes in, in one second, so in one second how? So inside the pipe, 4 kg is it possible? No. So same one kg that is going in, same one kg will, okay? And that is, should be equal to the rate of mass that is exiting from the, does this make sense? Which is equal to this mass which has gone inside. Is A1, V1, so I am getting Vm1 by 8 and assuming that the fluid is incompressible. Otherwise density will not remain in uniform, okay? Yes. No, non-viscous we are not assuming here right now, okay? We are assuming that fluid incompressible, greater than uniform. Same thing may not be valid for the air. Now, similarly, suppose V2A is the velocity, let's say it goes out, so this much water will go out, so this much distance will be V2DT, right? The rate of water is rho into A2 into, yes or no? V1, V is equal to A2V, then density will change, so the continuity equation will become rho 1, A1, any type of flow. Okay, so this is,