Hello, 1. The problem statement, all variables and given/known data I am trying to find an expression for the energy transferred into heat due to friction between layers of viscid fluid. I am provided with the following diagram (see attachment), and am instructed to first find the force at both ends of the cylinder exerted on the surface area of the cylinder of thickness dr, then multiply the force by the velocity, then integrate. 2. Relevant equations 3. The attempt at a solution F2 = P2*A = 2P2*pi*L*dr; F1 = P1*A = 2P1*pi*L*dr I believe the integration should hence be: Int[ΔP(R2-r2)/(4ηL)*2pi*L*dr] between 0 and R. Would that be correct? I am not sure.