First slide

A small sphere of radius‘r’ falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to


The viscous drag force, F=6πηrv

where v= terminal velocity

The rate of production of heat = power 

                                                                    = force ×times terminal velocity

 Power =6πηrv·v=6πηrv2

 Terminal velocity v=2r2(ρ-σ)g9η;


 Now, power =6πηr4r4(ρ-σ)281η2g2 or    Power r5 . 

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