You explained this incredibly well. Coming from an engineering student studying from home during the pandemic, your videos are a lifesavers. Thank you very much!
You are correct - if you look at the coordinate system that I draw at 1:42 you will see that the y-axis has a zero value at the center line of the channel.
Thank you. It's a really good explanation. But could I ask a question? what about the shear stress of the lower wall? if y= -0.25, then tau on fluid is positive,on the other hand, tau on wall is negative, so shear stress of the upper wall and lower wall are opposite directions. it's really confused.
My only question is that the "y" in your formula represented the distance between the plate and where Umax is located? Thank you for showing this example.
Also looking for a bit of clarification on this. I am assuming since we use Umax then we can also use y as the distance from the plate in the equation.
The coordinate system is defined at the centerline of the channel. The y in the last equation is the y-location of the upper wall - so half the channel width.
He explains in the video since the derivation for tau, mu times du/dy finds the shear on the fluid. We can then deduce that the shear on the plate is opposite in direction so flip the sign.
I think it came from interpolating the values from the table A.1 I interpolated and got 0.001155 so I guess it's about right with different tables and slightly different numbers
