Regarding the actual need to foresee transient flow with precision, linked with computacional developments occurred during last decades, simplified hypothesis has been eliminated searching computational results coherent with experimental results. Therefore, this work presents a friction model for newtonian flow in transient pipe flow. The continuity equation and momentum equation are solved numerically by finite-difference method regarding the transient aspect to determinate the friction factor. Both the basic model based in a fully developed flow and two approximations are presented in a systematic way. The results presented were developed to foresee the waterhammer showing a big difference between the two models for transient friction and the well-known steady friction model. Moreover,the influence of different parameters were investigated.