Consider the following statements:
1) In flow through hydro dynamically smooth pipes, the friction factor f is always a constant.
2) In flow through hydro dynamically smooth pipes, the friction factor f is always a function of the flow Reynolds number.
3) In a fully developed rough turbulent pipe flow, the friction factor f is a function of relative roughness only.
4) In a fully developed rough turbulent pipe flow, the friction factor f is a function of the flow Reynolds number and relative roughness.
Which of the above statements are correct?