At 7:00 is there not an extra negative there? I expected the integral of -d(psi) = -[psi2 - psi1] ... but this would break the explanation though, where am I making a mistake? Thanks!
you are right TIM , but the thing is the magnitude of psi 2 minus psi 1, for Q (AB) should be same as psi 1 minus psi 2 for Q (BC) .In conclusion volume flow rate across AB and BC are the same ,and you should notice that when you want to calculate magnitude of something you must put absolute sign around that | psi 2 minus psi 1 | = | psi 1 minus psi 2 |
@@afshincheraghchi9194 I disagree with you. Tim is right because by the process the uploader used, Q(BC) must be negative to Q(AB), and it is because the order of nodes is reversed. i. e. you will get the values the same when you calculating Q(CB). And I suppose simply adding an absolute value is not convincing since the sign actually implies the direction of the flow rate and there is conditions that we don't know this initially.
Hey guys if you actually see then check with the direction. If u see the line AB then the dir is perp to AB hence u is the comp. If you consider BC then he took v as the comp. So in the 1st case of AB dir is right of AB. In second case as we found negative I think the dir is in downwards direction. So I guess this is what the direction is trying to say.
Ur right. But the point is psi value at x2 is psi1 i.e. point C and psi value at x1 is psi2 i.e. point B. Now check the integral with negative sign you will get the same answer on both sides
@@marshallm.7421 Agree with you, perhaps if we stick with the coordinate B(x2, y2) and C(x3, y3) then it is less confusing. The integral then from x2 to x3, you will then have the integral result is -psi (from x2-x3). Plug it in the value at x3 is psi1 and at x2 is psi2: - psi1 -(- psi2) = psi2 - psi1.
Because it depends on which line u consider. If you consider line AB then you take flux perp to that vel city that is U comp. When u consider BC then u consider v comp that is perp to line BC.
Becoz he is taking Y as a constant and B is x1 which inturn makes C as x2. The initial assumption he made that Y is a constant and thats why both A and B have x1.
