What physical principle causes infalling material around a protostar to flatten into a rotating structure?

Answer

Conservation of angular momentum

As the material from a molecular cloud collapses gravitationally towards the center, the conservation of angular momentum dictates that this rotating material flattens into a disk structure surrounding the nascent star.

What physical principle causes infalling material around a protostar to flatten into a rotating structure?
Geologyprocessplanetmassaccretion