Good question! Note that R is the inside radius of a given pipe. It is a constant. Whereas, "r" is a variable, it is the radial distance that increases from the center of the pipe (where it is zero) to the inside pipe surface (where it will equal R).
thank u very much sir ,u made a good path for underpreviledge guys
Sir , at 4: 30 how you taken that pR^2 as constant...it is not constant it is radius...then the whole term should change?
Good question! Note that R is the inside radius of a given pipe. It is a constant. Whereas, "r" is a variable, it is the radial distance that increases from the center of the pipe (where it is zero) to the inside pipe surface (where it will equal R).
should stop using radius use diameter sames so many steps.... area = d squared x .7854