Homework Statement
I' have formula P=Po+(mg)/(π*r^2)
I need to derive it.
I have derived it P'(r)=(2mg/π(r^3))*Δr
but it's incorrect. The teacher wrote me "You have forgotten about ΔPo and Δm!"
I don't know how I could derive it. It's for mistake calculation in laborotory work!