My Fluid Mechanics teacher once told me, there are 2 types of friction factors (say, in connection with pipe flows). I remember, one is Darcy-Weisbachs' other one is Mannings (?). Wondering if there is a unified view (or) simply both are different ? can some learned soul clear my confusion.

THe other is Fanning. One of them is four times the other. Check a textbook.

(1) on which principle Hot Air baloon works ? & give the details of principle,with some more examples

Dear Basavaraj,

Hot air ballon works on the principle that when air becomes hot, it turns lighter and will try to go upward. This drives the balloon upward. Hoe this will help u

regards Kasyap

Read about buoyancy ...